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  • calcium  (147)
  • Springer  (147)
  • Alfred Wegener Institute for Polar and Marine Research & German Society of Polar Research
  • 2005-2009
  • 1985-1989  (147)
  • 1950-1954
Collection
Keywords
Publisher
  • Springer  (147)
  • Alfred Wegener Institute for Polar and Marine Research & German Society of Polar Research
  • Wiley-Blackwell  (37)
Years
Year
  • 1
    Electronic Resource
    Electronic Resource
    Dystrophin and the integrity of the sarcolemma in Duchenne muscular dystrophy (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 175-177 
    Details
    ISSN: 1420-9071
    Keywords: Dystrophin ; calcium ; skeletal muscle ; muscular dystrophy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary It is suggested that in Duchenne muscular dystrophy the absence of dystrophin, which is probably a cytoskeletal protein underlying the sarcolemma, causes changes in stretch-activated cation channels rather than direct mechanical tearing of the surface membrane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01954866
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  • 2
    Electronic Resource
    Electronic Resource
    Cerebrovascular autoregulation is resistant to calcium channel blockade with nimodipine (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 305-306 
    Details
    ISSN: 1420-9071
    Keywords: Baboon ; 133xenon ; cerebral blood flow ; cerebrovascular resistance ; autoregulation ; nimodipine ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In normal baboons cerebrovascular resistance changed along with blood pressure to maintain blood flow constant. This ‘autoregulation’ was not significantly altered in animals treated with a dose of the calcium channel blocker nimodipine causing selective cerebral vasodilation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01951818
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  • 3
    Electronic Resource
    Electronic Resource
    Morphological evidence for calcium storage in the chromatoid body of rat spermatids (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 377-378 
    Details
    ISSN: 1420-9071
    Keywords: Chromatoid body ; spermatids ; calcium ; microtubules ; morphology ; pyroantimonate ; rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Morphological evidence for probable Ca2+ storage in the vesicular elements of the rat spermatid chromatoid body is documented using the K-pyroantimonate method, combined with EDTA chelation. Some vesicles are related to the microtubules associated with the chromatoid body. A possible involvement of Ca2+ in the intracellular movement and/or structural integrity of the chromatoid body is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01957484
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  • 4
    Electronic Resource
    Electronic Resource
    Involvement of a Ca2+-calmodulin interaction in the yeast-mycelial (Y-M) transition of Candida albicans (1989)
    Springer
    Mycopathologia 108 (1989), S. 47-54 
    Details
    ISSN: 1573-0832
    Keywords: Candida albicans ; dimorphism ; yeast-mycelium transition ; calcium ; calmodulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A yeast-mycelium (Y-M) transition of Candida albicans (3153A) was induced by 1.5 mM CaCl2 · 2H2O in defined liquid medium, pH 7, at 25 °C. Germ tube formation was detected after approximately 8 h and peaks of maximum germination occurred at approximately 20 h in all experimental treatments. Non-toxic concentrations of the calmodulin inhibitor R24571 almost completely suppressed germ tube formation whereas trifluoperazine (TFP) and the Ca2+ ionophore A23187 were only about half as effective. Further Ca2+ addition failed to reverse the inhibitory effect of R24571 and induced only about 10% of the cells inhibited by TFP or A23187 to germinate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00436783
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  • 5
    Electronic Resource
    Electronic Resource
    Calcium movements during each heart beat (1989)
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 103-108 
    Details
    ISSN: 1573-4919
    Keywords: heart ; relaxation ; calcium ; sodium-calcium exchange
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Transsarcolemmal calcium movements are closely related to force generation in the heart. It is important to understand the transport pathways that control these movements of calcium across the sarcolemmal membrane. In the normal, beating heart, sodium-calcium exchange appears to be an important mechanism for the extrusion of calcium from the cell. The kinetics of this exchange are dependent upon the characteristics of the cell action potential. Calcium efflux via sodium-calcium exchange may be sufficient to balance calcium entry through calcium channels during the action potential.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220760
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  • 6
    Electronic Resource
    Electronic Resource
    Sodium-calcium exchange in mammalian heart: current-voltage relation and intracellular calcium concentration (1989)
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 97-102 
    Details
    ISSN: 1573-4919
    Keywords: calcium ; sodium ; fura-2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Membrane currents and changes in intracellular calcium ion concentration ([Ca2+]i) have been recorded that can be attributed to the operation of an electrogenic, voltage-dependent sodium-calcium (Na-Ca) exchanger in mammalian heart cells. Single guinea-pig ventricular myocytes under voltage clamp were perfused internally with the fluorescent Ca2+-indicator, fura-2, and changes in [Ca2+]i and membrane current that resulted from Na-Ca exchange were isolated through the use of various organic channel blockers (verapamil, TTX), impermeant ions (Cs+, Ni2+), and inhibitors of sarcoplasmic reticulum (ryanodine). The I-V relation of Na-Ca exchange was obtained from the Ni2+-sensitive current elicited by ramp repolarization from +90 mV to −80 mV. Ramps were sufficiently rapid that little change in [Ca2+]i occured during the ramp. The (constant) [Ca2+]i during the ramp was varied over the range 100 nM to 1000 nM by varying the amplitude and duration of a pre-pulse to the ramp. The reversal potential of the Ni2+-sensitive ramp current varied linearly with 1n([Ca2+])i. The I-V relations at different [Ca2+]i over the range −60 mV to +140 mV were in reasonable accord with the predictions of a simple, simultaneous scheme of Na-Ca exchange, on the basis that only [Ca2+]i had changed. The relationship between [Ca2+]i and current at a constant membrane voltage was also in accord with this scheme. We suggest that Ca2+-fluxes through the exchanger during the cardiac action potential can be understood quantitatively by considering the binding of Ca2+ to the exchanger during the [Ca2+]i-transient and the effects of membrane voltage on the exchanger.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220759
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  • 7
    Electronic Resource
    Electronic Resource
    Appraisal of the physiological relevance of two hypotheses for the mechanism of calcium release from the mammalian cardiac sarcoplasmic reticulum: calcium-induced release versus charge-coupled release (1989)
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 135-140 
    Details
    ISSN: 1573-4919
    Keywords: calcium ; heart ; sarcoplasmic reticulum ; excitation-contraction coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract Recent studies correlating the calcium current with, respectively, the clamp-imposed voltage and the calcium current in intact isolated mammalian cardiac myocytes are reviewed. The major findings are the following: [1] With the exception of one group, all investigators agree that a calcium transient is never observed in the absence of a calcium current. In addition, there is a good correlation between voltage dependence of the calcium current and that of the calcium transient, although this correlation may vary among the cardiac tissues from different animal species. [2] Repolarization clamp pulses from highly positive potentials produce a ‘tail current’ which is associated with a ‘tail calcium transient’. [3] The calcium transient is inhibited when the calcium current is blocked by calcium deprivation or substitution, or by the addition of calcium current antagonists, despite the fact that sarcoplasmic reticulum still contains calcium that can be released by caffeine (with inhibition of this release by ryanodine). These three findings are strongly in favor of a calcium-induced release of calcium and against the hypothesis of charge-movement-coupled release of calcium from the sarcoplasmic reticulum. [4] The only finding that would be more in favor of the latter hypothesis (although till reconciliable with the former) is that repolarization occurring before the rapid rise of calcium transient is complete curtails the calcium transient. Thus, the possibility that charge movement might somehow regulate calcium-induced release of calcium cannot be excluded.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220765
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  • 8
    Electronic Resource
    Electronic Resource
    The effect of acidosis on excitation-contraction coupling in isolated ferret heart muscle (1989)
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 169-173 
    Details
    ISSN: 1573-4919
    Keywords: pH ; calcium ; heart muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The contractile response to acidosis is the final product of a number of different changes in the excitation-contraction coupling pathway: (i) Cai increases and subsequently decreases during acidosis; (ii) the action potential becomes longer; (iii) the sensitivity of the contractile proteins to Ca2+ decreases. The increase of Cai and the lengthening of the action potential may help to maintain contractile function, although this advantage may be offset if spontaneous Ca2− release from the s.r. occurs, secondary to the increase of Cai. The recovery of force shown in figure 1 occurs at a time when the calcium transient is decreasing, and therefore represents an increasing sensitivity of the contractile proteins to Cai, probably due to a recovery of intracellular pH(6), although it is also possible that a disappearance of spontaneous Ca2+ releases from the s.r. may be contributing [2].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220771
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  • 9
    Electronic Resource
    Electronic Resource
    The contribution of mitochondrial calcium ion exchange to relaxation of tension in cardiac muscle (1989)
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 127-133 
    Details
    ISSN: 1573-4919
    Keywords: mitochondria ; sarcoplasmic reticulum ; calcium ; myocytes ; caffeine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The possible contribution of mitochondrial Ca2+ accumulation and release to contractile phenomena has been investigated. Two intracellular fractions of Ca2+ sequestration can be identified in cardiac myocytes, one ascribed to mitochondria. Two modes of Ca2+ transport exist within the mitochondrial fraction, one dependent upon mitochondrial respiration and the other upon extramitochondrial [Na+]. Experiments with trabeculae show that under appropriate conditions, the rate of relaxation and the amount of tension developed is dependent on these two modes of Ca2+ transport. A model is presented quantifying the contribution of the mitochondria to relaxation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220764
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  • 10
    Electronic Resource
    Electronic Resource
    The control of calcium influx by cytoplasmic calcium in mammalian heart muscle (1989)
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 109-113 
    Details
    ISSN: 1573-4919
    Keywords: heart muscle ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The role of Ca2+ in the initiation and maintenance of contraction has been extensively studies. Many of these studies have focused on how Ca2+ influx and efflux affect cytoplasmic Ca2+ (Cai) and, therefore, contraction in cardiac muscle. However, it has recently become apparent that Cai itself may play a major role in the control of Ca2+ influx and efflux from cardiac muscle. Here we review current ideas on the mechanisms underlying Ca2+ homeostasis in cardiac muscle, with specific attention to how Cai may control Ca2+ influx, both under normal and pathological conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00220761
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  • 11
    Electronic Resource
    Electronic Resource
    Redistribution of subcellular calcium in rat liver on administration of vanadate (1989)
    Springer
    Molecular and cellular biochemistry 90 (1989), S. 155-164 
    Details
    ISSN: 1573-4919
    Keywords: polyvanadate ; mitochondria ; calcium ; pyruvate dehydrogenase ; receptors
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Mitochondria isolated from the livers of rats administered with sodium meta-, ortho-, or polyvanadate, but not vanadyl sulphate, exhibited enhanced Ca2+ — stimulated respiration and uptake of calcium. These effects were shown also by mitochondria isolated from livers perfused with polyvanadate. The concentration of acid-soluble calcium decreased significantly in the mitochondrial fraction on vanadate treatment, while that in the cytosol showed a corresponding increase. Phenoxybenzamine, an antagonist to a-adrenergic receptors, effectively inhibited vanadate-induced Ca2+ mobilization, but surgical sympathectomy was without effect. This is the first demonstration of vanadate mimicking α-adrenergic agonists in vivo.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00221215
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  • 12
    Electronic Resource
    Electronic Resource
    ATP inhibits onset of exocytosis in permeabilised mast cells (1989)
    Springer
    Bioscience reports 9 (1989), S. 99-109 
    Details
    ISSN: 1573-4935
    Keywords: mast cells ; exocytosis ; G-protein ; GE ; calcium ; ATP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract ATP is not required for exocytosis from permeabilised mast cells, and therefore there is no direct role for protein phosphorylation in the late stages of the activation pathway. We have measured the timecourse of exocytosis from permeabilised cells triggered to release hexosaminidase following addition of Ca2+ to cells equilibrated for 2 min with GTP-γ-S. If ATP is included at the time of permeabilisation, then exocytosis commences after a delay, the duration of which depends on the square root of the product [Ca2+][GTP-γ-S], and which may extend to beyond 3 min. When ATP is excluded then the maximal rate of exocytosis is established within 3 secs of completing the effector combination. These results suggest that the achievement of a new steady-state, induced by Ca2+ and GTP-γ-S, and required for exocytosis is inhibited by ATP. From this we conclude that dephosphorylation of an unknown regulator protein may comprise a step in the exocytotic pathway.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01117516
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  • 13
    Electronic Resource
    Electronic Resource
    A comparison of bradykinin, angiotensin II and muscarinic stimulation of cultured bovine adrenal chromaffin cells (1989)
    Springer
    Bioscience reports 9 (1989), S. 243-252 
    Details
    ISSN: 1573-4935
    Keywords: secretion ; exocytosis ; chromaffin cell ; calcium ; bradykinin ; angiotensin II, muscarinic
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Bradykinin, angiotensin II and a mascarnic agonist, acetyl-B-methacholine (methacholine) were all found to elict catecholamine release from cultured bovine adrenal chromaffin cells. Bradykinin was the most potent of these secretagogues and methacholine the weakest, with angiotenin II intermediate in efficacy. All three secretagogues were much less effective than nicotinic stimulation. The three secretagogues all produced a rise in cytoplasmic free calcium concentration ([Ca2+]i), measured with the fluorescent indicator fura2, which was partially independent of external calcium. In the case of bradykinin the full rise in ([Ca2+]i) may involve a component of calcium entry in addition to release of calcium from an internal store. Secretion was also found to be partially independent of external calcium. The different efficacies of the three secretagogues in elicting secretion were correlated with the rise in ([Ca2+]i) produced. The differeing efficacies of the three secretagogues may be due to the extent of release of calcium from an intracellular store which itself is less effective in eliciting secretion than a rise in [Ca2+]i following calcium entry due to nicotine. Bradykinin also stimulates calcium entry, and this may increase the efficacy of the initial rise in [Ca2+]i. Treatment with pertussis toxin resulted in an enhancement of secretion in response to all of the secretagogues.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01116001
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  • 14
    Electronic Resource
    Electronic Resource
    A nonselective cation channel activated by membrane deformation in oocytes of the ascidianBoltenia villosa (1989)
    Springer
    The journal of membrane biology 107 (1989), S. 179-188 
    Details
    ISSN: 1432-1424
    Keywords: stretch-activated channel ; calcium ; oocyte ; development ; patch clamp ; tunicate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Cell-attached patch clamp recordings from unfertilized oocytes of the ascidianBoltenia villosa reveal an ion channel which is activated by mechanical deformation of the membrane. These channels are seen when suction is applied to the patch pipette, but not in the absence of suction or during voltage steps. The estimated density of these stretch-activated channels is about 1.5/μm2, a figure equal to or greater than the density of known voltage-dependent channels in the oocyte. Ion substitution experiments done with combined whole-cell and attached patch recording, so absolute potentials are known, indicate that the channel passes Na+, Ca2+ and K+, but not Cl−. The channel has at least two open and two closed states, with the rate constant that leaves the longer-lived closed state being the primary site of stretch sensitivity. External Ca2+ concentration affects channel kinetics: at low calcium levels, long openings predominate, whereas at high calcium virtually all openings are to the short-lived open state. In multiple channel patches, the response to a step change in suction is highly phasic, with channel open probability decreasing over several hundred milliseconds to a nonzero steady-state level after an initial rapid increase. This channel may play a role in the physiological response of cells of the early embryo to the membrane strains associated with morphogenetic events.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871723
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  • 15
    Electronic Resource
    Electronic Resource
    Role of calcium and calmodulin in the regulation of the rabbit ileal brush-border membrane Na+/H+ antiporter (1989)
    Springer
    The journal of membrane biology 108 (1989), S. 207-215 
    Details
    ISSN: 1432-1424
    Keywords: calcium ; calmodulin ; absorption ; ileum ; brush-border vesicle ; phosphorylation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In rabbit ileum, Ca2+/calmodulin (CaM) appears to be involved in physiologically inhibiting the linked NaCl absorptive process, since inhibitors of Ca2+/CaM stimulate linked Na+ and Cl− absorption. The role of Ca2+/CaM-dependent phosphorylation in regulation of the brush-border Na+/H+ antiporter, which is believed to be part of the neutral linked NaCl absorptive process, was studied using purified brush-border membrane vesicles, which contain both the Na+/H+ antiporter and Ca2+/CaM-dependent protein kinase(s) and its phosphoprotein substrates. Rabbit ileal villus cell brush-border membrane vesicles were prepared by Mg precipitation and depleted of ATP. Using a freezethaw technique, the ATP-depleted vesicles were loaded with Ca2+, CaM, ATP and an ATP-regenerating system consisting of creatine kinase and creatine phosphate. The combination of Ca2+/CaM and ATP inhibited Na+/H+ exchange by 45±13%. This effect was specific since Ca2+/CaM and ATP did not alter diffusive Na+ uptake, Na+-dependent glucose entry, or Na+ or glucose equilibrium volumes. The inhibition of the Na+/H+ exchanger by Ca2+/CaM/ATP was due to an effect on theV max and not on theK m for Na+. In the presence of CaM and ATP, Ca2+ caused a concentration-dependent inhibition of Na+ uptake, with an effect 50% of maximum occurring at 120nm. This Ca2+ concentration dependence was similar to the Ca2+ concentration dependence of Ca2+/CaM-dependent phosphorylation of specific proteins in the vesicles. The Ca2+/CaM/ATP-inhibition of Na+/H+ exchange was reversed by W13, a Ca2+/CaM antagonist, but not by a hydrophobic control, W12, or by H-7, a protein kinase C antagonist. we conclude that Ca2+, acting through CaM, regulates ileal brush-border Na+/H+ exchange, and that this may be involved in the regulation of neutral linked NaCl absorption.
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    URL: http://dx.doi.org/10.1007/BF01871735
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  • 16
    Electronic Resource
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    Ca2+-activated K+ channels from cultured renal medullary thick ascending limb cells: Effects of pH (1989)
    Springer
    The journal of membrane biology 110 (1989), S. 49-55 
    Details
    ISSN: 1432-1424
    Keywords: loop of Henle ; potassium secretion ; channels ; acid/base balance ; thick ascending limb ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Ca2+-activated K+ channels were studied in cultured medullary thick ascending limb cells (MTAL) using the patch-clamp technique. The purpose was to determine the effect of acidic pH on channel properties in excised patches of apical cell membrane. At pH 7.4, increasing Ca2+ on the intracellular side or applying positive voltages increases channel open probability. Reducing pH to 5.8 on the intracellular face of the channel decreases channel open probability at each voltage and Ca2+ concentration. Channel mean open times display two distributions and mean closed times display three distributions. Increasing Ca2+ or applying depolarizing voltages lengthens each of the mean open times and shortens each of the closed times. Lowering pH to 5.8 decreases the mean open times and increases mean closed times at each Ca2+ and voltage with the greatest effect on the mean closed times. In contrast, both single-channel conductance and channel kinetics are unaffected when pH is reduced to 5.8 on the extracellular face of the membrane. We conclude that protons interfere with Ca2+ binding to the gate of Ca2+-activated K+ channels reducing the probability of channel opening.
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    URL: http://dx.doi.org/10.1007/BF01870992
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  • 17
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    Ca2+ and cAMP activate K+ channels in the basolateral membrane of crypt cells isolated from rabbit distal colon (1989)
    Springer
    The journal of membrane biology 110 (1989), S. 19-28 
    Details
    ISSN: 1432-1424
    Keywords: colon ; ion transport ; ion channel ; cyclic nucleotides ; calcium ; potassium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Using patch-clamp techniques, we have studied Ca2+-activated K+ channels in the basolateral membrane of freshly isolated epithelial cells from rabbit distal colon. Epithelial cell clusters were obtained from distal colon by gentle mechanical disruption of isolated crypts. Gigaohm seals were obtained on the basolateral surface of the cell clusters. At the resting potential (approximately −45 mV), with NaCl Ringer's bathing the cell, the predominant channels had a conductance of 131±25 pS. Channel activity depended on voltage as depolarization of the membrane increased the open probability. In excised inside-out patches, channels were found to be selective for K+ over Na+. Channel activity correlated directly with bath Ca2+ concentration in the excised patches. Channel currents were blocked by 5mm TEA+ and 1mm Ba2+. In cell-attached patches, after addition of the Ca2+ ionophore A23187, which increases intracellular Ca2+, open probability was markedly increased. Channel activity was also regulated by cAMP as addition of 1mm dibutyryl-cAMP in the bath solution in cell-attached patches increased channel open probability over 20-fold. Channels that had been activated by cAMP were further activated by Ca2+. We conclude that the basolateral membrane of epithelial cells from descending colon contains a class of potassium channels, which are regulated by intracellular Ca2+ and cAMP.
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    URL: http://dx.doi.org/10.1007/BF01870989
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  • 18
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    c-src Locus determines increased rate of Na+, K+-cotransport and increased calcium content in (SHR×WKY)F2 hybrid erythrocytes (1989)
    Springer
    Bulletin of experimental biology and medicine 108 (1989), S. 1634-1636 
    Details
    ISSN: 1573-8221
    Keywords: c-src locus ; calcium ; Na+, K+-cotransport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00839709
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  • 19
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    Desensitization of the nicotinic acetylcholine receptor: Molecular mechanisms and effect of modulators (1989)
    Springer
    Cellular and molecular neurobiology 9 (1989), S. 141-178 
    Details
    ISSN: 1573-6830
    Keywords: specific desensitization ; nicotinic acetylcholine receptor ; molecular mechanisms ; affinity transitions ; modulators of desensitization ; noncompetitive blockers ; calcium ; substance P ; thymic hormones ; thymopoietin ; thymopentin ; calcitonin gene-related peptide ; receptor phosphorylation ; receptor methylation ; myasthenia gravis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Loss of response after prolonged or repeated application of stimulus is generally termed desensitization. A wide variety of phenomena occurring in living organisms falls under this general definition of desensitization. There are two main types of desensitization processes: specific and non-specific. 2. Desensitization of the nicotinic acetylcholine receptor is triggered by prolonged or repeated exposure to agonists and results in inactivation of its ion channel. It is a case of specific desensitization and is an intrinsic molecular property of the receptor. 3. Desensitization of the nicotinic acetylcholine receptor at the neuromuscular junction was first reported by Katz and Thesleff in 1957. Desensitization of the receptor has been demonstrated by rapid kinetic techniques and also by the characteristic “burst kinetics” obtained from single-channel recordings of receptor activity in native as well as in reconstituted membranes. In spite of a number of studies, the detailed molecular mechanism of the nicotinic acetylcholine receptor desensitization is not known with certainty. The progress of desensitization is accompanied by an increase in affinity of the receptor for its agonist. This change in affinity is attributed to a conformational change of the receptor, as detected by spectroscopic and kinetic studies. A four-state general model is consistent with the major experimental observations. 4. Desensitization of the nicotinic acetylcholine receptor can be potentially modulated by exogenous and endogenous substances and by covalent modifications of the receptor structure. Modulators include the noncompetitive blockers, calcium, the thymic hormone peptides (thymopoietin and thymopentin), substanceP, the calcitonin gene-related peptide, and receptor phosphorylation. Phosphorylation is an important posttranslational covalent modification that is correlated with the regulation and desensitization of the receptor through various protein kinases. 5. Although the physiological significance of desensitization of the nicotinic receptor is not yet fully understood, desensitization of receptors probably plays a significant role in the operation of the neuronal networks associated in memory and learning processes. Desensitization of the nicotinic receptor could also possibly be related to the neuromuscular disease, myasthenia gravis.
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    URL: http://dx.doi.org/10.1007/BF00713026
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  • 20
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    Effects of addition of calcium and magnesium salts on ammonia volatilization during manure decomposition (1989)
    Springer
    Plant and soil 115 (1989), S. 53-58 
    Details
    ISSN: 1573-5036
    Keywords: ammonia volatilization ; calcium ; magnesium ; manure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Ammonia volatilization during aerobic decomposition of poultry manure was significantly reduced through additions of calcium and magnesium salts. The percentage reduction in ammonia loss decreased during the 48 day decomposition period from 85–100% in the first 2–3 weeks, to 23–52% at the end of the experiment. The maximum amount of ammonia which was retained (i.e. maximum reduction in ammonia loss) through addition of the chloride salts of Mg2+ or Ca2+ was independent of the type of cation. However, CaCl2 released some of the ammonia initially retained as production of CO2 and NH3 from the manure decreased after 3 weeks of decomposition, whereas both MgCl2 and MgSO4 did not release any of the initially retained ammonia over the 7 week incubation period. Over the entire incubation period MgCl2 therefore retained more ammonia than CaCl2. Magnesium sulphate was considerably less effective in retaining ammonia than either chloride salts.
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    URL: http://dx.doi.org/10.1007/BF02220694
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  • 21
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    Aluminium and manganese and their relation to calcium in soil solution and needles in three Norway spruce (Picea abies, L. Karst.) stands of Upper Austria (1989)
    Springer
    Plant and soil 114 (1989), S. 257-267 
    Details
    ISSN: 1573-5036
    Keywords: aluminium ; calcium ; manganese ; needles ; soil solution ; spruce ; toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Soil solution and needles of three mature spruce stands in Upper Austria were analysed in order to investigate the uptake and possible toxic effects of Mn and Al, as these two elements become highly mobilised in the soil due to increasing acidity. The Ca/Al molar ratio in the soil solution was below 0.2 in the most damaged stand during almost the whole vegetation period. Despite different dynamics, Al reaches almost identical values in all stands at the end of the vegetation period in both 1-year (current) and 2-year-old needles, respectively. Therefore, needle analysis is not a useful tool for estimation of free Al in the soil. Needle contents of other elements could provide a better information for understanding the forest decline. Mn in the needles correlates significantly with Mn concentrations in the soil solution. As soil Mn will be mobilised by acidic input, Mn needle content can increase to very high levels. Manganese distribution, its interaction with calcium, and possible toxic effects are discussed.
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    URL: http://dx.doi.org/10.1007/BF02220806
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    In situ ion exchange resin bags to estimate forest site quality (1989)
    Springer
    Plant and soil 119 (1989), S. 186-190 
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    ISSN: 1573-5036
    Keywords: ammonium ; calcium ; forest soil ; ion exchange resin ; magnesium ; manganese ; nitrate ; phosphorus ; soil analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Cation and anion exchange resin bags were placed just under the humus layer at five adjacent forest sample sites with differing site quality classes in order to assess the available nutrient supply. For comparison, humus samples were collected from the same sites. Nutrients were extracted from humus samples by conventional extraction methods and by shaking together with ion exchange resin bags. Ca and Mg corresponded best to differences in site quality class, of all analysed ions in thein situ resin bag eluates. Thein situ resin bag adsorption of NH4−N, Na and Mn also showed a positive correlation with site quality. The adsorption of PO4−P was negatively correlated to site quality class. Inadequate amounts of exchange resin, or leaving resin bagsin situ for too long a time result in the replacement of already adsorbed ions by ions with higher ion exchange constants.
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    Honeylocust (Gleditsia triacanthos L.) root response to aluminium and calcium (1989)
    Springer
    Plant and soil 119 (1989), S. 181-185 
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    ISSN: 1573-5036
    Keywords: aluminium toxicity ; calcium ; honeylocust ; root biomass ; root branching ; soil acidification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Honeylocust (Gleditsia triancanthos L.) root growth response to varying levels of Al and Ca in soil solutions was examined in two horizons each of two forest soils. With results from all four horizons combined, multiple regression analysis indicated that both Ca and Al were significant (p〈0.01) factors affecting root elongation, branching and biomass production. Over a wide range of Al and Ca concentrations in soil solutions from four different soil horizons, the Ca:Al ratio was a significantly better predictor of honeylocust root response to acid soils than Al or Ca alone.
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    Ca2+ interaction with phospholipid bilayers studied by multifrequency phase fluorometry (1989)
    Springer
    Bioscience reports 9 (1989), S. 497-502 
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    ISSN: 1573-4935
    Keywords: calcium ; phosphatidate ; DPH ; phase fluorometry ; distributional analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Calcium interaction with phospholipid membranes containing phosphatidic acid is studied by multifrequency phase fluorometry, using DPH as fluorescent molecule. DPH decay is analysed by a continuous distribution of lifetimes. The results suggest an increase of membrane heterogeneity at low calcium concentrations, without changes in the polarity of the environment surrounding the probe.
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    URL: http://dx.doi.org/10.1007/BF01117053
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    Calcium absorption in man: Some dosing recommendations (1989)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 17 (1989), S. 631-644 
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    ISSN: 1573-8744
    Keywords: calcium ; absorption ; efficiency ; dosing ; regimens
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The absorption of calcium involves a saturable (active) and a nonsaturable (passive) component. The work of several investigators indicates that an inverse relationship exists between calcium intake and absorption efficiency. Human calcium absorption data from the literature were analyzed using a model which included both an active and a passive absorption component. Simulations were provided to illustrate the suitability of this model, and another previously reported model, to fit the data and to estimate the absorption efficiency of calcium when using different dosing regimens. Comparisons of the values predicted in this study with some literature values are provided and some assumptions and potential limitations associated with the use of this method are discussed. The division of the daily dose into equal increments taken at equally spaced intervals over the course of the day is recommended as a useful procedure for increasing the absorption efficiency and efficacy of calcium.
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    Effect of deicing chloride salts on ion accumulation in spruce (Picea abies (L.) sp.) (1989)
    Springer
    Plant and soil 113 (1989), S. 3-11 
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    ISSN: 1573-5036
    Keywords: calcium ; chlorine ; ion selectivity ; injury ; Picea ; potassium ; retranslocation ; sodium ; uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Among the inorganic chloride salts, NaCl, CaCl2 and in a minor proportion KCl and MgCl2 are used as deicing agents. Mixturs of these salts were merely applied with respect to their physico-chemical properties, but their effect on roadside vegetation has never been studied so far. From a screening of different salt mixtures on ion accumulation in needles and twigs of spruce tress (Picea abies sp.) it was shown that the presence of a small amount of calcium in the salt treatments had some beneficial effects on ion regulation. In the presence of calcium, sodium accumulation could be reduced. But more straightforward was its effect on the selectivity between sodium and potasium in favour of the latter. Chloride concentrations did not alter very much; their role in the presence of monovalent cations is nevertheless obvious and is discussed. The study also confirms the presence of potassium retranslocation in conifer trees. The ion characteristics are briefly discussed with respect to the ecological effects of chloride salts on tress.
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    Coupling of strontium and calcium cycles in Lake Constance (1989)
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    Hydrobiologia 176-177 (1989), S. 323-329 
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    ISSN: 1573-5117
    Keywords: strontium ; calcium ; coprecipitation ; Lake Constance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The contents of Sr and Ca were measured weekly in Lake Constance in 1986. Epilimnetic concentrations of Ca changed between 1.30 × 10-3 mol l-1 (during homothermy) and 0.9 × 10 -3 mol l-1 (during thermal stratification). The seasonal fluctuations of Ca were correlated with those of Sr (between 4.61 and 5.36 μmol l-1). The epilimnion was permanently oversaturated with respect to calcite but not with respect to SrCO3. Analysis of the settling process by use of sedimentation traps revealed two short episodes of very high authigenic settling fluxes of CaCO3, triggered by phytoplankton diatoms. Seasonal changes of the Ca contents (between 4.1 and 30.7 percent of the dry weight) and of the Sr concentrations (from 12 to 75 × 10-3 percent) in the settling material were closely correlated. This suggests a coprecipitation mechanism with a nearly constant stoichiometry of (atoms Sr/atoms Ca) × 1000 of 0.84. Coprecipitation of Sr or Ca with organic matter was insignificant. In the hypolimnion some Sr and Ca were released from the settling material. These results strongly suggest that the cycle of Sr in Lake Constance is driven predominantly by coprecipitation with calcite. The principal chemical mechanisms leading to coprecipitation are discussed.
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    Contribution of dissolved calcium and magnesium to phytoplanktonic particulate phosphorus concentration at the heads of two river reservoirs (1989)
    Springer
    Hydrobiologia 183 (1989), S. 185-193 
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    ISSN: 1573-5117
    Keywords: reservoir ; phytoplanktonic particulate phosphorus ; regulation ; calcium ; magnesium ; multiple regression analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract At the heads of two river reservoirs, the Ishitegawa Dam and the Nomura Dam Reservoirs in Japan, the concentrations of phytoplanktonic particulate phosphorus (PP) were compared with those of dissolved calcium (Ca) and magnesium (Mg), using multiple regression analyses on the data taken from samples which registered more than 6.0 µg l−1 in chlorophyll a concentration. Of the 27 monthly samples, 16 from the Ishitegawa Reservoir and 17 from the Nomura Reservoir were used. A significant regression line, logPP = k 1F + k 2, was obtained, where k 1 (〉 0) and k 2 were constants and F (named the Ca-Mg index) consisted of log(Ca/Mg) − 0.5 log(ca + Mg) in mol concentration in Ca and Mg, in common with the two reservoirs (r 2 = 0.730 & 0.913).
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    Signals controlling renin release in aglomerular toadfish (1989)
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    Fish physiology and biochemistry 7 (1989), S. 323-329 
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    ISSN: 1573-5168
    Keywords: renin release ; aglomerular teleost ; toadfish ; isoproterenol ; cyclic AMP ; cyclic GMP ; calcium ; calcium channel ; K+ depolarization ; baroreceptor ; calcium channel antagonist
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The toadfish,Opsanus tau, lacks renal glomeruli and macula densa, but has high renal renin activity and abundant granulated cells in renal arteries and arterioles. Reduction of blood pressure (BP) or blood volume by hemorrhage or vasodilatory drugs causes renin release, indicating that an intrarenal or extrarenal pressure- or volume-sensitive mechanism exists for controlling renin release in the toadfish. Thus, we examined whether 1) β-adrenergic receptor-mediated activation of renin release, and 2) calcium influx which may underlie the baroreceptor mechanism are involved in the cellular control of renin release. Acute injection of isoproterenol (1 μg/kg, n = 6) decreased BP and increased plasma renin activity (PRA) 4–5 fold in unanesthetized toadfish. Propranolol abolished both effects, but did not decrease basal PRA levels.In vitro superfusion of renal slices with bicarbonate Ringer's solution showed a steady secretion of renin, and addition of 50 mM K+ (K+ methylsulfate replacing NaCl, n = 10) to the superfusate markedly suppressed renin secretion. Nifedipine (10−5 M, n = 8) completely restored the high K+-induced inhibition of renin secretion from renal slices, whereas isoproterenol (10−4 M, n = 6) neither increased basal renin secretion nor restored K+-induced renin suppression. These results suggest that calcium influx may mediate inhibitory messages for renin secretion, while the β-adrenoceptor-mediated activation of granulated cells appears absent in toadfish.
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    Studies on the structure and physiology of salmon teleocalcin (1989)
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    Fish physiology and biochemistry 7 (1989), S. 367-374 
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    ISSN: 1573-5168
    Keywords: teleocalcin ; calcium ; corpuscles of Stannius ; gill function ; prolactin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The structure and physiology of salmon teleocalcin, a Ca+2 regulating hormone from the corpuscles of Stannius (CS) is reviewed. Teleocalcin is produced by the PAS+, type 1 cells in the CS. The hormone is a disulfide-linked homodimer, with a unique amino acid sequence and a carbohydrate moiety on residue 29. The teleocalcin monomer has a MW of 30 KD, whereas the pro-form of the monomer is 32 KD. The hormone is positively regulated by Ca+2 and its function is to slow the active transport of Ca+2 across the gill epithelium. In conjunction with prolactin, which stimulates Ca+2 transport, teleocalcin is one of the major factors involved in Ca+2 homeostasis in fish.
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    Effect of pod zone moisture content on reproductive growth in three cultivars of peanut (Arachis hypogaea) (1989)
    Springer
    Plant and soil 116 (1989), S. 111-114 
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    ISSN: 1573-5036
    Keywords: calcium ; moisture ; peanut ; pod zone ; reproductive growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Very little research has been done to investigate the effect of a dry podding zone on reproductive development in peanut plants that are otherwise well hydrated via subsoil moisture extraction. The influence of podding zone moisture content on reproductive development and growth of three peanut cultivars (McCubbin, Gajah and Robut 33-1) was investigated in pots grown in the glasshouse. In two cultivars (McCubbin and Gajah) seed yield was reduced in a dry (air-dry) compared to a wet (field capacity) podding zone. Seed yield of Robut 33-1 was unaffected by podding zone moisture content, indicating that cultivar variation in reproductive performance in response to podding zone moisture may exist.
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    Adsorption ofRhizobium meliloti to alfalfa roots: Dependence on divalent cations and pH (1989)
    Springer
    Plant and soil 117 (1989), S. 67-74 
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    ISSN: 1573-5036
    Keywords: bacterial adsorption ; calcium ; magnesium ; Medicago sativa ; pH ; Rhizobium meliloti ; root surface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Adsorption ofRhizobium meliloti L5-30 in low numbers to alfalfa (Medicago sativa L.) roots was dependent on the presence of divalent cations, and required neutral pH. Adsorption was proportional to Ca and/or Mg concentrations up to 1.5 mM. Ca was not substituted by Sr, Ba or Mn. Adsorption was abolished and viability decreased at pH≤6. When lowering pH, higher Ca concentrations were required to attain similar adsorption levels, indicating a marked interactive effect between Ca and H ions. Pretreatment of the roots with Ca and low pH did not affect subsequent adsorption of the bacteria. However, Ca pretreatment ofR. meliloti sustained further adsorption at low Ca levels and low pH substantially affected their ability to adsorb. Low pH appears to affect the stability of binding causing desorption of the previously bound bacteria. The presence of saturating concentrations of heterologousR. leguminosarum bv.trifolii A118, did not prevent the expression of divalent cations and pH requirements, as well as their interaction. Our results suggest that rhizobial binding to the root surface already shows the Ca and pH dependence of alfalfa nodulation, which was generally associated to some event prior to rhizobial penetration of root hairs.
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    Adenine and pyridine nucleotide levels during calcium-induced conidiation in Penicillium notatum (1989)
    Springer
    Antonie van Leeuwenhoek 56 (1989), S. 191-199 
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    ISSN: 1572-9699
    Keywords: calcium ; conidiation ; nucleotides ; nucleotide charges ; Penicillium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Concentrations of adenine and pyridine nucleotides and the associated charge values were examined in extracts of mycelium of Penicillium notatum during vegetative growth and reproductive development promoted by the addition of Ca2+ (10 mmol dm-3). The significant increase in adenylate energy charge promoted by Ca2+ was due to a fall in intracellular AMP and a concomitant rise in ATP concentration. Intracellular concentrations of NADH and NAD fell within 1 h of the addition of Ca2+. The catabolic reduction charge was unchanged by Ca2+ whilst the anabolic reduction charge increased in Ca2+-induced mycelium due to lowered intracellular NADP concentration. Reduced concentration of NADPH in Ca2+-induced mycelium, relative to the vegetative controls, lowered the phosphorylated nucleotide fraction. The results are discussed in relation to metabolic economy during morphogenesis in P. notatum.
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    Nutritional disturbances of young pines in a dry heath forest (1989)
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    Plant and soil 113 (1989), S. 229-235 
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    ISSN: 1573-5036
    Keywords: aluminium ; calcium ; foliar analysis ; magnesium ; nitrogen ; nutritional disturbance ; Pinus sylvestris L. ; potassium ; soil analysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Tree decline has been observed recently in 25–30 year old pine stands inCladina andCalluna-type heath forests in the Hämeenkangas and Pohjankangas areas of southwestern Finland. The trees had grown more or less normally for 15 years. During the following 7 to 8 years increased growth occurred. From 1982 to 1984, however, the trees revealed a sudden reduction in height increment. Additionally, some trees were marked by poor apical shoot dominance. Occasionally complete crown dieback was observed. The trees retained only one to three years' needles. These needles often were characterized by a brownish yellow discoloration. Chemical foliar and soil analysis indicate both a nitrogen deficiency and a deficiency in calcium and magnesium related to the relatively high aluminium levels in the soil. In the needles of affected trees phosphorus and especially potassium concentrations were higher than normally. The low content of nitrogen, calcium and magnesium in the soil is related to the acidic, nutrient-poor bedrock, and the low cation exchange capacity. Also the leaching of nutrients, the shallow and poor quality of the humus layer, and the removal of nutrients by tree harvesting may have effected on the nutritional disturbances.
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    Effect of deicing NaCl and CaCl2 on spruce (Picea abies (L.) sp.) (1989)
    Springer
    Plant and soil 120 (1989), S. 203-211 
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    ISSN: 1573-5036
    Keywords: calcium ; chlorine ; climate ; injury ; Picea ; rating ; sodium ; soil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract NaCl and CaCl2 are frequently used as deicing agents during the winter season. The present study compares the effect of these deicing salts on salt injury on spruce trees (Picea abies sp.). From two field experiments carried out for ten weeks during the winter period of 1986–1987, and a total dose of 1.5 kg m−2 NaCl, CaCl2 or a 75/25 NaCl/CaCl2 mixture, it was found that the presence of calcium clearly reduced the salt injury as was indicated by salt tolerance ratings. These ratings corresponded well to the Cl− concentrations found in needles and twigs. Though an equal dose of Cl− was given, in the presence of CaCl2 the uptake of Cl− was inhibited. Surely the role of calcium on ion permeability in salinized soil should have its effect, together with the regulatory role that calcium has on ion accumulation and transport. Furthermore it was found that the climatic conditions and the calcium status of the soil only have an effect on the time of appearance of the injury.
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    The Role of Calcium Ions and Bile Salts on the Pancreatic Lipase-Catalyzed Hydrolysis of Triglyceride Emulsions Stabilized with Lecithin (1989)
    Springer
    Pharmaceutical research 6 (1989), S. 449-457 
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    ISSN: 1573-904X
    Keywords: pancreatic lipase ; lipase ; lipolysis ; triglycerides ; kinetics ; mechanism ; calcium ; bile salts ; lecithin ; emulsions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Lecithin-stabilized triglyceride emulsions are subject to hydrolysis by pancreatic lipase. The time profiles of these reactions are characterized by a lag-phase and a zero-order phase. Lag phases are more pronounced with long-chain triglycerides. Ca2+ is effective in reducing the lag-phase and activating lipase. Kinetic analysis of the reactions suggests that, like previous findings by others, taurodeoxycholate (TDC) micellar solutions combine with the lipase–colipase complex to form another catalytically active enzyme form. This enzyme form exhibits reduced activity in the absence of Ca2+. In the presence of Ca2+ the mixed micelle–lipase complex becomes more active and opens a new pathway for lipolysis. It is suggested that this enzyme form can bind more easily to interfaces with different physicochemical properties. Under these conditions, Ca2+ activates the lipolysis of short-, medium-, and long-chain triglycerides by a similar mechanism. Maximum activities were measured in the presence of approximately 6 mM TDC and 30 mM Ca2+. The experimental conditions approximate the physiological conditions in the gastrointestinal tract since all of the factors studied here have been reported to be necessary for in vivo lipolysis and/or absorption of triglycerides. A mechanistic model for lipolysis in the presence of Ca2+ and the bile salt TDC is proposed which accounts for most of the experimental observations in a quantitative manner.
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    Autoradiographic study of human epidermocytes cultured in a low calcium medium (1989)
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    Bulletin of experimental biology and medicine 107 (1989), S. 574-577 
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    ISSN: 1573-8221
    Keywords: epidermocytes ; calcium ; multiplication ; autoradiographic investigation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    Cellular mechanisms of transient contraction of coronary arterial smooth muscles in hypoxia: Role of intracellular Ca++ (1989)
    Springer
    Bulletin of experimental biology and medicine 107 (1989), S. 3-6 
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    ISSN: 1573-8221
    Keywords: hypoxia ; coronary spasm ; calcium ; sarcoplasmic reticulum ; inositol-1,4,5-triphosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00837042
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    Arachidonic acid mobilization in platelets: The possible role of protein kinase C and G-proteins (1988)
    Springer
    Cellular and molecular life sciences 44 (1988), S. 101-104 
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    ISSN: 1420-9071
    Keywords: Platelets ; calcium ; phospholipase A2 ; G-proteins ; arachidonic acid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A major route for the release of arachidonic acid from platelet phospholipids appears to be catalyzed by a phospholipase A2 that can be stimulated by a rise of cytosolic Ca2+. This paper discusses certain other mechanisms for regulation of this process. Release of arachidonic acid by calcium ionophores is potentiated by pretreatment with stimulators of protein kinase C; e.g. diglyceride, phorbol esters and the terpene diester mezerein. This effect appears to be coincident with phosphorylation of a certain group of proteins (not 47 KDa protein), and is sensitive to depletion of ATP, activation of Ca2+ dependent phosphatase, and the kinase C inhibitor H-7, but is unaffected by Na+/H+ exchange inhibitors. Recent results in other cell types strongly indicate that phospholipase A2 is also directly under control of certain GTP-binding proteins.
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    Ionic currents in morphogenesis (1988)
    Springer
    Cellular and molecular life sciences 44 (1988), S. 657-666 
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    ISSN: 1420-9071
    Keywords: Ionic currents ; vibrating probe ; membrane potential ; fucoid egg polarization ; animal-vegetal polarity ; polarization ; voltage gradients ; calcium ; vesicle secretion ; Achlya ; oocytes ; insect follicle ; insect ovariole ; polarized transport ; egg activation ; mouse blastomere ; epithelial morphogenesis ; limb bud
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Morphogenetic fields must be generated by mechanisms based on known physical forces which include gravitational forces, mechanical forces, electrical forces, or some combination of these. While it is unrealistic to expect a single force, such as a voltage gradient, to be the sole cause of a morphogenetic event, spatial and temporal information about the electrical fields and ion concentration gradients in and around a cell or embryo undergoing morphogenesis can take us one step further toward understanding the entire morphogenetic mechanism. This is especially true because one of the handful of identified morphogens is Ca2+, an ion that will not only generate a current as it moves, but which is known to directly influence the plasma membrane's permeability to other ions, leading to other transcellular currents. It would be expected that movements of this morphogen across the plasma membrane might generate ionic currents and gradients of both electrical potential and intracellular concentration. Such ionic currents have been found to be integral components of the morphogenetic mechanism in some cases and only secondary components in other cases. My goal in this review is to discuss examples of both of these levels of involvement that have resulted from investigations conducted during the past several years, and to point to areas that are ripe for future investigation. This will include the history and theory of ionic current measurements, and a discussion of examples in both plant and animal systems in which ionic currents and intracellular concentration gradients are integral components of morphogenesis as well as cases in which they play only a secondary role. By far the strongest cases for a direct role of ionic currents in morphogenesis is the polarizing fucoid egg where the current is carried in part by Ca2+ and generates an intracellular concentration gradient of this ion that orients the outgrowth, and the insect follicle in which an intracellular voltage gradient is responsible for the polarized transport from nurse cell to oocyte. However, in most of the systems studied, the experiments to determine if the observed ionic currents are directly involved in the morphogenetic mechanism are yet to be done. Our experience with the fucoid egg and the fungal hypha ofAchlya suggest that it is the change in the intracellular ion concentration resulting from the ionic current that is critical for morphogenesis.
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    Effect of cation exchange on the distribution and movement of cations in soils with variable charge. I. Effect of lime on potassium and magnesium exchange equilibria (1988)
    Springer
    Nutrient cycling in agroecosystems 17 (1988), S. 21-30 
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    ISSN: 1573-0867
    Keywords: Potassium ; magnesium ; calcium ; aluminium ; exchange coefficient ; equilibrium activity ratio ; organic matter ; bonding strength
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The influence of Ca(OH)2 on K and Mg exchange equilibria in three New Zealand soils was studied. Calcium hydroxide was mixed with each soil to raise the pH to about 6 or 7. For each Ca(OH)2 treatment, K and Mg exchange isotherms were determined, from which the equilibrium activity ratios were derived. Exchange coefficients and solution activity ratios were calculated according to the Gapon convention. The addition of Ca(OH)2 produced varying effects in the Gapon exchange coefficient for both K and Mg. The magnitude and direction of change in the exchange coefficient were related to the cation initially dominating the exchange sites, rate of Ca(OH)2 addition, soil colloids contributing to the CEC and specific interactions of Ca with these soil colloids. Addition of Ca(OH)2 reduced the equilibrium activity ratio of all soils. Changes in the bonding strength of K and Mg with increasing CEC were suggested as a possible mechanism for this decrease.
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    Development of the myocardial contractile system (1988)
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    Cellular and molecular life sciences 44 (1988), S. 936-944 
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    ISSN: 1420-9071
    Keywords: Contractile system ; fetus ; premature myocardium ; calcium ; sarcoplasmic reticulum ; contractile protein ; sarcolemma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Recent studies regarding developmental changes in the myocardial contractile system from fetal, newborn, and adult animals are reviewed. From the data obtained so far, we conclude that in the early fetus myocardial contraction is mainly dependent on Ca which enters via the sarcolemma. Ca release from the sarcoplasmic reticulum is minimal. The role of the sarcoplasmic reticulum as a source of contractile Ca increases and the role of Ca influx across the sarcolemma in contractile system decreases with development.
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    Regulation of calcium handling by rat parotid acinar cells (1988)
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    Molecular and cellular biochemistry 82 (1988), S. 67-73 
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    ISSN: 1573-4919
    Keywords: neurotransmitter control ; secretion ; exocrine ; salivary gland ; calcium ; ATP-dependent calcium transport
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Salivary gland fluid secretion following neurotransmitter stimulation is Ca2+-dependent. We have studied the control of cellular Ca2+ following secretory stimuli in rat parotid gland acinar cells. After muscarinic-cholinergic receptor activation, cytosolic Ca2+ is elevated 4–5 fold, due to both intracellular Ca2+ pool mobilization and extracellular Ca2+ entry. Fluid movement ensues due to the Ca2+-activated enhancement of membrane permeability to K+ and Cl−. Basal cytosolic Ca2+ levels are tightly controlled at ∼150–200 nM through the action of high affinity and high capacity ATP-dependent Ca2+ transporters in the basolateral and endoplasmic reticulum membranes. Activity of these Ca2+ transporters can be modulated to facilitate rapid responsiveness and a sustained fluid secretory response necessary for alimentary function.
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    Ca2+ ionophores inhibit superoxide generation by chemotactic peptide in rabbit neutrophils and the correlation with intracellular calcium (1988)
    Springer
    Molecular and cellular biochemistry 84 (1988), S. 97-103 
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    ISSN: 1573-4919
    Keywords: neutrophils ; A23187 ; lasalocid ; calcium ; superoxide ; chemotactic peptide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Summary Effects of Ca2+ ionophores, A23187 and lasalocid, on superoxide anion generation by chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine methyl ester, in rabbit peritoneal exudate neutrophils were studied. The ionophores by themselves did not activate superoxide anion generation in these neutrophils. When preincubated with the cells for 2 min, both the ionophores inhibited superoxide generation induced by chemotactic peptide. The inhibition was present even in the absence of extracellular Ca2+ and the inhibition was better then. Lasalocid produces a dose-dependent chlortetracycline fluorescence decrease response in neutrophils loaded with chlortetracycline. This response is independent of extracellular Ca2+ concentration and is related to release of Ca2+ from intracellular storage sites. The dose-range at which lasalocid gives this response is same as the dose-range at which it causes inhibition of superoxide response. It may be concluded that the inhibition of superoxide generation by these ionophores is correlated to intracellular Ca2+ modulation.
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    Dissociation of the metabolic from the contractile response to muscarinic stimulation in the rabbit urinary bladder (1988)
    Springer
    Molecular and cellular biochemistry 81 (1988), S. 137-143 
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    ISSN: 1573-4919
    Keywords: bladder ; muscarinic stimulation ; metabolism ; bethanecol ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: Abstract The calcium dependence of contraction and NADH flurorescence was investigated in rabbit bladder stimulated with bethanechol or KCl. The absence of calcium in the bathing solution induced a rightward shift in the dose response to bethanechol for both contraction and NADH flurorescence. The contractile response was shifted to a greater degree than the fluorescence response and the maximal response to bethanechol was reduced by 80% for contraction but only 20% for NADH fluorescence. This rightward shift was also induced by the benzothiazepine calcium antagonist diltiazem (200 μM) and again the contractile response was shifted significantly more than the fluorescence response. The combination of zero calcium and 200 μM diltiazem virtually abolished contractions but only inhibited the NADH fluorescence by 65% at maximally effective bethanechol concentrations. Unlike the effect of diltiazem on the response to bethanechol, diltiazem (200 μM) shifted both the contraction and fluorescence curves to the right equally in response to KCl stimulation. These results indicate that a metabolic response to muscarinic stimulation (decreased NADH) can occur in the absence of any observable contractile response. This metabolic response may be due to post receptor signal processing events. For KCl stimulation, the NADH response is probably secondary to and a result of the contractile response.
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    A novel role of Ca2+ and Zn2+: Protection of cells against membrane damage (1988)
    Springer
    Bioscience reports 8 (1988), S. 579-583 
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    ISSN: 1573-4935
    Keywords: calcium ; zinc ; membrane protection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Certain cytotoxic agents damage cells by the induction of pores across their plasma membrane. Ca2+ and Zn2+ protect against such damage by promoting pore closure. Zn2+ may play a beneficial role in this regard in certain disease states.
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    URL: http://dx.doi.org/10.1007/BF01117337
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    Defective regulation of apical membrane chloride transport and exocytosis in cystic fibrosis (1988)
    Springer
    Bioscience reports 8 (1988), S. 27-33 
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    ISSN: 1573-4935
    Keywords: cystic fibrosis ; chloride transport ; exocytosis ; calcium ; calmodulin ; B-adrenergic ; cyclic AMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract A biochemical link is proposed between recent observations on defective regulation of Cl− transport in CF respiratory epithelial cells and studies showing altered biological activity of calmodulin in exocrine glands from CF patients. A consensus is emerging that defective β-adrenergic secretory responsiveness in CF cells is caused by a defect in a regulator protein at a site distal to cyclic AMP formation. Our results indicate that this protein might be a specific calmodulin acceptor protein which modifies the activity of calmodulin in epithelial cells. Alteration in Ca2+/calmodulin dependent regulation of Cl− transport and protein secretion could explain (i) alterations in Ca2+ homeostasis seen in CF, (ii) defective β-adrenergic responses of CF cells, and (iii) the observed inability of cyclic AMP (acting via its specific protein kinase, A-kinase) to open apical membrane Cl− channels in CF epithelial cells. Most of the physiological abnormalities of CF including elevated sweat electrolytes and hyperviscous mucus can be explained on this basis.
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    Exocytosis reconstituted from the sea urchin egg is unaffected by calcium pretreatment of granules and plasma membrane (1988)
    Springer
    Bioscience reports 8 (1988), S. 335-343 
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    ISSN: 1573-4935
    Keywords: calcium ; exocytosis ; sea urchin egg ; phosphoinositide ; diacylglycerol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Micromolar calcium ion concentrations stimulate exocytosis in a reconstituted system made by recombining in the plasma membrane and cortical secretory granules of the sea urchin egg. The isolated cortical granules are unaffected by calcium concentrations up to 1 mM, nor do granule aggregates undergo any mutual fusion at this concentration. Both isolated plasma membrane and cortical granules can be pretreated with 1 mM Ca before reconstitution without affecting the subsequent exocytosis of the reconstituted system in response to micromolar calcium concentrations. On reconstitution, aggregated cortical granules will fuse with one another in response to micromolar calcium provided that one of their number is in contact with the plasma membrane. If exocytosis involves the generation of lipid fusogens, then these results suggest that the calcium-stimulated production of a fusogen can occur only when contiguity exists between cortical granules and plasma membrane. They also suggest that a substance involved in exocytosis can diffuse and cause piggy-back fusion of secretory granules that are in contact with the plasma membrane. Our results are also consistent with a scheme in which calcium ions cause a reversible, allosteric activation of an exocytotic protein.
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    Ca2+-activated K+ channels in the apical membrane ofNecturus choroid plexus (1988)
    Springer
    The journal of membrane biology 105 (1988), S. 207-219 
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    ISSN: 1432-1424
    Keywords: choroid plexus ; brush border membrane ; Ca2+-activated K+ channels ; calcium ; barium ; TEA ; intracellular pH ; cerebrospinal fluid secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The properties of Ca2+-activated K+ channels in the apical membrane of theNecturus choroid plexus were studied using single-channel recording techniques in the cell-attached and excised-patch configurations. Channels with large unitary conductances clustered around 150 and 220 pS were most commonly observed. These channels exhibited a high selectivity for K+ over Na+ and K+ over Cs+. They were blocked by high cytoplasmic Na+ concentrations (110mm). Channel activity increased with depolarizing membrane potentials, and with increasing cytoplasmic Ca2+ concentrations. Increasing Ca2+ from 5 to 500nm, increased open probability by an order of magnitude, without changing single-channel conductance. Open probability increased up to 10-fold with a 20-mV depolarization when Ca2+ was 500nm. Lowering intracellular pH one unit, decreased open probability by more than two orders of magnitude, but pH did not affect single-channel conductance. Cytoplasmic Ba2+ reduced both channel-open probability and conductance. The sites for the action of Ba2+ are located at a distance more than halfway through the applied electric field from the inside of the membrane. Values of 0.013 and 117mm were calculated as the apparent Ba2+ dissociation constants (K d (0 mV) for the effects on probability and conductance, respectively. TEA+ (tetraethylammonium) reduced single-channel current. Applied to the cytoplasmic side, it acted on a site 20% of the distance through the membrane, with aK d (0 mV)=5.6mm. A second site, with a higher affinity,K d (0 mV)=0.23mm, may account for the near total block of chanel conductance by 2mm TEA+ applied to the outside of the membrane. It is concluded that the channels inNecturus choroid plexus exhibit many of the properties of “maxi” Ca2+-activated K+ channels found in other tissues.
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    Ca2+-activated K+ currents inNecturus choroid plexus (1988)
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    The journal of membrane biology 105 (1988), S. 221-231 
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    ISSN: 1432-1424
    Keywords: choroid plexus ; calcium-activated potassium currents ; cerebrospinal fluid secretion ; calcium ; delayed currents ; patch clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The tight-seal whole-cell recording method has been used to studyNecturus choroid plexus epithelium. A cell potential of −59±2 mV and a whole cell resistance of 56±6 MΩ were measured using this technique. Application of depolarizing step potentials activated voltage-dependent outward currents that developed with time. For example, when the cell was bathed in 110mm NaCl Ringer solution and the interior of the cell contained a solution of 110mm KCl and 5nm Ca2+, stepping the membrane potential from a holding value of −50 to −10 mV evoked outward currents which, after a delay of greater than 50 msec, increased to a steady state in 500 msec. The voltage dependence of the delayed currents suggests that they may be currents through Ca2+-activated K_ channels. Based on the voltage dependence of the activation of Ca2+-activated K+ channels, we have devised a general method to isolate the delayed currents. The delayed currents were highly selective for K+ as their reversal potential at different K+ concentration gradients followed the Nernst potential for K+. These currents were reduced by the addition of TEA+ to the bath solution and were eliminated when Cs+ or Na+ replaced intracellular K+. Increasing the membrane potential to more positive values decreased both the delay and the half-times (t 1/2) to the steady value. Increasing the pipette Ca2+ also decreased the delay and decreasedt 1/2. For instance, when pipette Ca2+ was increased from 5 to 500nm, the delay andt 1/2 decreased from values greater than 50 and 150 msec to values less than 10 and 50 msec. We conclude that the delayed currents are K+ currents through Ca2+-activated K+ channels. At the resting membrane potential of −60 mV, Ca2+-activated K+ channels contribute between 13 to 25% of the total conductance of the cell. The contribution of these channels to cell conductance nearly doubles with membrane depolarization of 20–30 mV. Such depolarizations have been observed when cerebrospinal fluid (CSF) secretion is stimulated by cAMP and with intracellular Ca2+. Thus the Ca2+-activated K+ channels may play a specific role in maintaining intracellular K+ concentrations during CSF secretion.
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    Ionic and permeability requirements for exocytosis in vitro in sea urchin eggs (1988)
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    The journal of membrane biology 101 (1988), S. 199-207 
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    ISSN: 1432-1424
    Keywords: exocytosis ; membrane fusion ; secretion ; calcium ; sea urchin egg ; cortical granule
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We study exocytosis in the planar isolated cortex of the egg of the sea urchinLytechinus pictus. Solutins bathing the exocytotic apparatus need not contain appreciable amounts of ions: fusion follows addition of submicromolar calcium to solutions containing only nonelectrolyte. We examine the effects of altering the granule membrane permeability to small molecules with ionophores and digitonin. Introducing holes in the secretory granule membrane to the extent of allowing free passage of small molecules does not cause seretion in vitro. We add the amphipathic compound digitonin at 12 to 15 μM concentrations and demonstrate that the granule membrane can become permeable to lucifer yellow, yet that granules remain intact. Granules still undergo exocytosis after digitonin treatment at such concentrations upon subsequent addition of calcium. Higher concentrations of digitonin lead to granule content swelling and vesicle bursting. We conclude that cortical granule hydration during exocytosis is not mediated by small ionic channels.
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    Transcellular ion currents and extension ofNeurospora crassa hyphae (1988)
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    The journal of membrane biology 101 (1988), S. 33-41 
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    ISSN: 1432-1424
    Keywords: electric current ; protons ; Neurospora crassa ; pH gradient ; H+-ATPase ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Hyphae ofNeurospora crassa, like many other tipgrowing organisms, drive endogenous electric currents through themselves such that positive charges flow into the apical region and exit from the trunk. In order to identify the ions that carry the current, the complete growth medium was replaced by media lacking various constituents. Omission of K+ or of phosphate diminished the zone of inward current, effectively shifting the current pattern towards the apex. Omission of glucose markedly reduced both inward and outward currents; addition of sodium azide virtually abolished the flow of electric current. Growing hyphae also generate a longitudinal pH gradient: the medium surrounding the apex is slightly more alkaline than the bulk phase, while medium adjacent to the trunk turns acid. The results suggest thatNeurospora hyphae generate a proton current; protons are expelled distally by the H+-ATPase and return into the apical region by a number of pathways, including the symport of protons with phosphate and potassium ions. Calcium influx may also contribute to the electric current that enters the apical region. There seems to be no simple obligatory linkage between the intensity of the transcellular electric current and the rate of hyphal extension. Calcium ions, however, are required in micromolar concentrations for extensions and morphogenesis of hyphal tips.
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    Evidence implicating protein kinase C in exocytosis from electropermeabilized bovine chromaffin cells (1988)
    Springer
    The journal of membrane biology 104 (1988), S. 21-34 
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    ISSN: 1432-1424
    Keywords: exocytosis ; secretion ; calcium ; protein kinase C ; adrenal medulla ; catecholamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The calcium sensitivity of exocytosis from electroper-meabilized chromaffin cells is increased by activators of protein kinase C, such as TPA and certain phorbol esters, diacylglycerols, and mezerein. A range of putative inhibitors of protein kinase C block both the phorbol ester-sensitive component of secretion and also the underlying insensitive component. These inhibitors are also shown to inhibit medulla protein kinase C activity in vitro. The extent of secretion is reduced when electropermeabilized cells are exposed to Ca2+ levels much in excess of 50 μm. The onset of inhibition is faster than the relatively slow rate of Ca-dependent exocytosis and is insensitive to inhibitors of proteolysis. Adrenal medulla protein kinase C activity is also irreversibly inhibited by high Ca2+ concentrations. Both the secretory response and the protein kinase C activity in vitro have similar nucleotide and cation specificities. Although these data do not definitely establish an involvement of protein kinase C in exocytosis, none argue against it.
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    Lowering the stimulated free intracellular calcium level in platelets in the refractory state (1988)
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    Bulletin of experimental biology and medicine 106 (1988), S. 1699-1702 
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    ISSN: 1573-8221
    Keywords: platelets ; aggregation ; refractoriness ; calcium ; ADP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00802170
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    Homeostatic role of anticalcitonin antibodies in calcium metabolism in experimental diabetes mellitus (1988)
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    Bulletin of experimental biology and medicine 105 (1988), S. 181-183 
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    ISSN: 1573-8221
    Keywords: diabetes mellitus ; calcium ; anticalcitonin antibodies ; reaction of enzyme-labeled antibodies
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    Correlation between calcium biorhythms and helio-geophysical factors (1988)
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    Bulletin of experimental biology and medicine 105 (1988), S. 244-247 
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    ISSN: 1573-8221
    Keywords: biorhythms ; calcium ; immunization ; helio-geophysical rhythms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00835707
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    Effects of trypsin on secretion stimulated by micromolar Ca2+ and phorbol ester in digitonin-permeabilized adrenal chromaffin cells (1988)
    Springer
    Cellular and molecular neurobiology 8 (1988), S. 115-128 
    Details
    ISSN: 1573-6830
    Keywords: adrenal gland ; chromaffin cells ; phorbol ester ; digitonin ; secretion ; calcium ; trypsin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Catecholamine secretion from digitonin-treated chromaffin cells is stimulated directly by micromolar Ca2+ in the medium. The permeabilized cells are leaky to proteins. 2. In this study trypsin (30–50µg/ml) added to cells after digitonin treatment completely inhibited subsequent Ca2+-dependent catecholamine secretion. The same concentrations of trypsin did not inhibit secretion from permeabilized cells if trypsin was present only prior to cell permeabilization. 3. The data indicate that trypsin entered digitonin-treated chromaffin cells which were capable of undergoing secretion and that an intracellular, trypsinsensitive protein is involved in secretion. Chymotrypsin was less potent but had effects similar to those of trypsin. 4. The enhancement of Ca2+-dependent secretion from permeabilized chromaffin cells induced by the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) was inhibited by trypsin added simultaneously with Ca2+ to permeabilized cells at concentrations (3–10µg/ml) which had little or no effect on Ca2+-dependent secretion from cells untreated with TPA. Ca2+-dependent secretion in TPA-treated cells was reduced by trypsin only to the level that would have occurred in cells not treated with TPA. Trypsin reduced the large TPA-induced increment of membrane-bound protein kinase C. 5. The data indicate that Ca2+-dependent secretion in the absence of TPA does not require aTPA-like effect of Ca2+ to activate protein kinase C. Protein kinase C activation by TPA probably enhances Ca2+-dependent secretion by modulating the normal Ca2+-dependent pathway or by activating another Ca2+-dependent pathway which functions in parallel to the normal pathway.
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    Dual regulation of ACTH secretion by guanine nucleotides in permeabilized AtT-20 cells (1988)
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    Cellular and molecular neurobiology 8 (1988), S. 129-138 
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    ISSN: 1573-6830
    Keywords: GTP-binding proteins ; calcium ; exocytosis ; guanine nucleotides ; adrenocorticotropic hormone (ACTH) ; AtT-20 cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. We have examined the effects of guanine nucleotides on ACTH secretion from digitonin-permeabilized AtT-20 cells, with the aim of analyzing the involvement of GTP-binding proteins (G proteins) in the secretory process. 2. AtT-20 cells permeabilized with 20µM digitonin displayed calciumdependent secretion. The EC50 of calcium was ~2µM and the maximal stimulation was 350% of basal release. 3. Nonhydrolyzable guanine nucleotides also stimulated ACTH release, in a virtually Ca2+-free medium. The EC50 of guanosine 5′-(3-O-thio)triphosphate (GTP γ S) was ~15µM and the maximal stimulation was ~230% of basal release. The effects of calcium and guanine nucleotides were not additive. 4. In the presence of the inhibitory hormone, somatostatin guanine nucleotides inhibited the calcium-stimulated secretion. 5. Both the stimulatory and the inhibitory effects on secretion of guanine nucleotides were independent of changes in cyclic AMP (cAMP) and calcium. It is suggested that G proteins influence an unknown step in the secretion process, which would be near or at the exocytotic site. 6. The results can be explained by assuming the existence of two types of G proteins, one with stimulatory effects on exocytotic release (GeS) and another with inhibitory effects (GeI).
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    The effect of mineral elements on the maturity of peanut seed (1988)
    Springer
    Plant and soil 106 (1988), S. 263-268 
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    ISSN: 1573-5036
    Keywords: calcium ; lipid ; peanut(Arachis hypogaea) ; potassium ; starch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A greenhouse study was conducted to determine the effect, of certain nutrient elements, on the maturing peanut. Peanut fruits were grown in fruiting zones, which contained a complete nutrient medium, for 15 days. Individual plants were then cultured to maturity whilst allowing the fruit to develop in a nutrient medium which contained the complete nutrient (N, P, K, Ca, Mg and B) from which one element had been excluded. Except in the ‘minus B’ treatment, the basal seed weighed more than 500 mg. In the head seed the “minus Ca” treatment produced the lowest number of seeds which weighed 500 mg or more and P, K and B deficiencies produced not quite such low numbers of seeds above 500 mg. When basal and head seeds were grouped into 3 grades of fresh weights, those from Ca and K deficiencies produced smaller dry weights in seeds harvested on the 80th day. Seeds from a Ca deficient medium had a smaller lipid content and an increased sugar content. The starch content of the seed was decreased by K deficiency.
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    Uptake and distribution of mineral nutrients in muskmelon seedlings under nitrogen and phosphorus stresses and during recovery (1988)
    Springer
    Plant and soil 112 (1988), S. 273-278 
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    ISSN: 1573-5036
    Keywords: calcium ; chlorophyll ; Cucumis melo L. ; magnesium ; plant growth ; potassium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Muskmelon seedlings were grown hydroponically in a greenhouse and starved of nitrogen and/or phosphorus for 4 weeks. They were then transferred to an optimal N and P regime or to the opposite stress for an additional 3-week period. Nitrogen stress reduced markedly N, Ca, and chlorophyll contents of leaves and stems, but increased P content. Phosphorus stress reduced significantly P and K concentrations in stems and leaves but did not affect markedly chlorophyll content and did not result in N accumulation. Both stresses reduced significantly the area of the first leaf mainly by adversely affecting cell division. Repair of N and P concentrations in deficient seedlings by transfer to the optimal nutrition regime was more rapid in N- than in P-stressed seedlings.
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    Effect of salinity on phosphate accumulation and injury in soybean (1988)
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    Plant and soil 105 (1988), S. 25-32 
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    ISSN: 1573-5036
    Keywords: calcium ; cultivars ; foliar injury ; Glycine max ; phosphate uptake ; sodium ; solution cultures ; soybean ; toxicity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Many soybean [Glycine max (L.) Merr.] genotypes that are grown in solution cultures are highly sensitive to the combination of both salinity and inorganic phosphate (Pi) in the substrate. This effect has been observed on numerous occasions on plants grown in a saline medium that contained a substantial amount of Ca (i.e., CaCl2/NaCl=0.5 on a molar basis). Because Ca is important in regulating ion transport and membrane permeability, solution culture experiments were designed to examine the effects of various concentrations of Pi and ratios of CaCl2/NaCl (0 to 0.5 on a molar basis) at a constant osmotic potential (−0.34 MPa) on this adverse interaction. Four soybean cultivars (‘Lee’, ‘Lee 74’ ‘Clark’ and ‘Clark 63’) were tested. No adverse salinity x Pi interaction was found on Lee at any ratio and leaf P and Cl were maintained below 300 and 200 mmol kg−1 dry wt, respectively. Clark, Clark 63 and Lee 74 soybean plants, on the other hand, were severely injured by solution salinity (−0.34 MPa osmotic potential) when substrate Pi was ≥0.12 mM. Reduced substrate Ca did not intensify the salinity x Pi interaction. On the contrary, the onset of injury was hastened and more severe with increased CaCl2/NaCl ratios in isotonic solutions. Shoot and root growth rates decreased as injury increased. Leaf P concentrations from these cultivars grown in saline solutions with 0.12 mM Pi were excessive (〉600 mmol kg−1 dry wt) compared with concentrations commonly found in soybean leaf tissue yet they were independent of the severity of injury. Since leaf Cl increased wiht increased CaCl2/NaCl ratio, we suspect that the severity of foliar injury was related to the combined effects of excessive P and Cl within the tissue. Lee 74, the only injured cultivar examined that excluded Cl from its leaves, was less sensitive than either Clark cultivar and its injury was characteristically different. Other ion interactions were reported that may have played a role in injury susceptibility.
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    Ecology of deepwater rice-fields in Bangladesh 2. Chemistry of sites at Manikganj and Sonargaon (1988)
    Springer
    Hydrobiologia 169 (1988), S. 23-30 
    Details
    ISSN: 1573-5117
    Keywords: deepwater rice ; water chemistry ; diel change ; oxygen ; anoxic ; calcium ; Eichhornia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The chemistry of water in fields at two Bangladesh deepwater rice locations is compared. Although Manikganj lies in the Jamuna (-Brahmaputra) floodplain and Sonargaon in the old Meghna floodplain, their chemistries during the flood season are similar, apart from higher Mg % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGadiiEayaara% aaaa!3703!\[\bar x\]: 3.57 v.1.8 mg 1−1), Ca (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGadiiEayaara% aaaa!3703!\[\bar x\]: 13.1 v.4.5 mg l−1 ), pH and total alkalinity at the former. Diel changes in oxygen and sometimes also pH were evident 10 cm below the surface in deepwater rice fields, but such changes were typically much greater in fallow fields. Measurements made between 1400 and 1600 h in a range of habitats showed a trend for high pH values to be associated with high O2 values. Water in Eichhornia beds had the lowest values, deepwater rice fields were intermediate and fallow fields and other open areas typically had the highest values. O2 concentrations in excess of 15 mg l−1 and pH values of about 10.0 sometimes occurred in fallow fields with dense masses of submerged plants and loosely associated algal flocs. There was an increasing tendency for the water to become anoxic towards the end of the season and water 10 cm above the bottom was almost or entirely anoxic in deepwater rice fields at both locations over the whole 24-h period of 4/5 October, at a time when the depth of the water was starting to drop. Nitrite increased and sulphate decreased at both locations towards the end of the season.
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    Management of forest nursery soils dominated by calcium salts (1988)
    Springer
    New forests 2 (1988), S. 173-193 
    Details
    ISSN: 1573-5095
    Keywords: salinity ; calcium ; seedling nutrition ; lime-induced chlorosis ; fertilization ; soil management
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Soils that contain high levels of calcium salts can affect tree seedling growth in two ways: high total salts can reduce water availability, and excess calcium can affect seedling nutrition. Nutritional problems, such as iron deficiency (“lime-induced chlorosis”) and phosphorus deficiency, can seriously affect forest nursery production through growth losses, stunting, and sometimes seedling mortality. High calcium soils can be diagnosed by visible symptoms, soil tests, and seedling nutrient analysis. Soil management practices that have been used to treat high calcium soils include site selection and soil mapping, species and stock type selection, fertilization, and soil acidification. Cultural practices, including irrigation, mulching, deep ripping, organic matter amendments, and mycorrhizal treatments, have been used to lessen the adverse affects of high calcium soils.
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    URL: http://dx.doi.org/10.1007/BF00029987
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    Artemia habitats: Ion concentrations tolerated by one superspecies (1988)
    Springer
    Hydrobiologia 158 (1988), S. 201-214 
    Details
    ISSN: 1573-5117
    Keywords: Artemia ; saline lakes ; calcium ; Holocene ; Mono Lake ; Great Salt Lake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The geographic distribution, history, and ionic composition of habitats of Artemia franciscana are reviewed with emphasis on habitats with extreme values for ionic concentrations or ionic ratios: a) high-chloride waters (sea water salterns and Zuni and Great Salt Lakes); b) high-sulfate lakes in Saskatchewan (Chaplin and Little Manitou) and on the Okanogan plateau of Washington (Penley Lake complex); and c) high-carbonate habitats in Nevada (Fallon), in California (Mono Lake) and in the Nebraska sandhills (Jesse and Antioch). First-instar nauplii from populations representative of each of these three habitat clusters were tested for tolerance of potassium (0–5 g K l-1), magnesium (0–1.3 g Mg l-1), and calcium (0\2–0.6 g Ca l-1). Viabilities were recorded until survivors reached adulthood in pairs of simple defined synthetic culture media which differed in only one parameter. Eight populations showed four levels of tolerance of high potassium. Of four populations tested, all had high viability and fertility in media lacking potassium (above the level in the yeast diet). Artemia from sea water salterns or from Zuni, Chaplin, or Great Salt Lakes could not tolerate low levels of calcium (〈20 mg l-1). This accounts for their inability to tolerate hypersaline high-carbonate waters. Mono and Fallon nauplii had high viability and fertility in media with low levels of calcium (0–10 mg l-1) but lacking magnesium. They could not survive for seven days, however, in low-calcium (〈 10 mg l-1) media that contained moderate amounts of magnesium (1.3 g l-1), indicating that magnesium interferes with utilization of low levels of calcium. For each of the three cations, the range of concentrations encountered by each population in the habitat is narrower than the range affording high viability in laboratory media. As expected, the midpoints of the two ranges are sometimes similar. In many cases, however, the narrower range of ionic concentrations reported for lake water is at the end of the range affording high viability in the laboratory.
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    Nutrient release from decomposing foliar litter of three tree species with spicial reference to calcium, magnesium and potassium dynamics (1988)
    Springer
    Plant and soil 110 (1988), S. 49-55 
    Details
    ISSN: 1573-5036
    Keywords: Acer rubrum ; calcium ; cations ; Cornus florida ; decomposition ; litter ; magnesium ; nitrogen ; nutrient release ; phosphorous ; potassium ; Quercus prinus ; sulfur
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Calcium, magnesium and potassium dynamics in decomposing litter of three tree species were measured over a two-year period. The speices studied were flowering dogwood (Cornus florida), red maple (Acer rubrum) and chestnut oak (Quercus prinus). The order of decomposition was:C. florida〉A. rubrum〉Q. prinus. Calcium concentrations increased following any initial leaching losses. However, there were net releases of Ca from all three litter types since mass loss exceeded the increases in concentration. Net release of Ca by the end of two years from all three species combined was 42% of initial inputs in litterfall. Magnesium concentrations increased in the second year, following decreases due to leaching during the first year inC. florida andA. rubrum litter. Net release of Mg by the end of two years was 58% of initial inputs. Potassium concentrations decreased rapidly and continued to decline throughout the study. Net release of K by the end of two years was 91% of initial inputs. These data on cation dynamics, and similar data on N, S and P dynamics from a previous study, were combined with annual litterfall data to estimate the release of selected nutrients from foliar litter of these tree species at the end of one and two years of decomposition. The relative mobility of all six elements examined in relation to mass loss after two years was; K〉Mg〉mass〉Ca〉S〉P〉N.
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    Seasonal dynamics of major cations in xylem sap and needles of Norway spruce (Picea abies L. Karst.) in stands with different soil solution chemistry (1988)
    Springer
    Plant and soil 110 (1988), S. 91-100 
    Details
    ISSN: 1573-5036
    Keywords: calcium ; deficiency ; magnesium ; needles ; nutrition ; nutrient mobilisation ; potassium ; seasonal dynamics ; soil solution ; soil water ; spruce ; xylem sap
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Soil solution, xylem sap and needles of mature trees were sampled in three spruce stands over one vegetation period and analysed for major cations. Investigations of nutrient distribution between these three pools and evaluations of seasonal dynamics give the following results: The highest nutrient concentrations in the xylem sap occur at the time of bud break and become gradually lower during the vegetation period. The trees show similar trends of xylem sap concentrations with time for potassium, calcium and magnesium regardless of the nutritional status of the plots. No coupling of xylem sap to soil solution composition can be observed in spite of a high variability of soil solution chemistry in time. The major cations in the current needles exhibit a significantly different trend with time. No time-based correlations for nutrient contents could be found for the needles from the previous year. Despite mobilisation of storage pools in the deficient stand, trees are not able to increase the Ca and Mg contents in the needles up to the level of the other stands. Potassium could be retranslocated in sufficient extent for nutrition of current needles. Due to seasonal variability and dependence upon internal processes, such as retranslocation and mobilisation of nutrients, xylem sap does not seem to be a good tool for the estimation of the nutritional status of forest sites. It was concluded that only minor transport into new foliage via xylem sap will proceed after nutrient flush during the bud break and the nutrient content in the new biomass will be governed by dilution due to biomass growth or by nutrient transport by other means than xylem sap.
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    Properties of mitochondria from Penicillium cyclopium and their response to calcium and other divalent cations (1988)
    Springer
    Antonie van Leeuwenhoek 54 (1988), S. 221-228 
    Details
    ISSN: 1572-9699
    Keywords: calcium ; cation ; conidiation ; mitochondria ; respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The respiratory properties of isolated mitochondria from P. cyclopium were studied with particular attention to their response to calcium ions. The results obtained indicate concentration dependent stimulation of NADH oxidation by calcium ions. Similar effects could also be obtained with other divalent cations.
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    URL: http://dx.doi.org/10.1007/BF00443580
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    Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica II. Cacao and wood production, litter production and decomposition (1988)
    Springer
    Agroforestry systems 6 (1988), S. 37-48 
    Details
    ISSN: 1572-9680
    Keywords: Theobroma cacao ; shade trees ; Erythrina poeppigiana ; Cordia alliodora ; modelling ; organic matter ; nitrogen ; phosphorus ; potassium ; calcium ; magnesium ; litter production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract During 7 years (1979–1985) cacao harvests (beans and husks) have been recorded for the agroforestry systems ofTheobroma cacao underCordia alliodora andErythrina poeppigiana shade trees. The mean oven dry cacao yields were 626 and 712 kg.ha−1.a−1 cocoa beans underC. alliodora andE. poeppigiana respectively. Harvests have gradually increased over the years and the plantation has now reached maturity. Annual extraction of N, P, K, Ca and Mg in fruits, which is relatively small, was calculated on the basis of chemical analyses. The following average values were found (kg.ha−1.a−1): At the age of 8 years, theC. alliodora trees have reached 26.7 cm diameter (DBH) and 14.0 m in height. Mean annual growth (from age 5 to 7) is 14.6 m3.ha−1.a−1. Natural plant residue production has been measured for 4 years (Nov. 1981–Oct. 1985). UnderE. poeppigiana it has reached a value of 8.91 t.ha−1.a−1 and underC. alliodora 7.07 t.ha−1.a−1. The shade trees have contributed 57 and 47% respectively. Transference and decomposition rates are high and important in the nutrient cycles. The nutrient content of the litter was analysed and corresponding average yearly transfers were (kg.ha−1.a−1):
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    Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica II. Cacao and wood production, litter production and decomposition (1988)
    Springer
    Agroforestry systems 6 (1988), S. 37-48 
    Details
    ISSN: 1572-9680
    Keywords: Theobroma cacao ; shade trees ; Erythrina poeppigiana ; Cordia alliodora ; modelling ; organic matter ; nitrogen ; phosphorus ; potassium ; calcium ; magnesium ; litter production
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract During 7 years (1979–1985) cacao harvests (beans and husks) have been recorded for the agroforestry systems ofTheobroma cacao underCordia alliodora andErythrina poeppigiana shade trees. The mean oven dry cacao yields were 626 and 712 kg.ha−1.a−1 cocoa beans underC. alliodora andE. poeppigiana respectively. Harvests have gradually increased over the years and the plantation has now reached maturity. Annual extraction of N, P, K, Ca and Mg in fruits, which is relatively small, was calculated on the basis of chemical analyses. The following average values were found (kg.ha−1.a−1): At the age of 8 years, theC. alliodora trees have reached 26.7 cm diameter (DBH) and 14.0 m in height. Mean annual growth (from age 5 to 7) is 14.6 m3.ha−1.a−1. Natural plant residue production has been measured for 4 years (Nov. 1981–Oct. 1985). UnderE. poeppigiana it has reached a value of 8.91 t.ha−1.a−1 and underC. alliodora 7.07 t.ha−1.a−1. The shade trees have contributed 57 and 47% respectively. Transference and decomposition rates are high and important in the nutrient cycles. The nutrient content of the litter was analysed and corresponding average yearly transfers were (kg.ha−1.a−1):
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    URL: http://dx.doi.org/10.1007/BF02220107
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    Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica III. Cycles of organic matter and nutrients (1988)
    Springer
    Agroforestry systems 6 (1988), S. 49-62 
    Details
    ISSN: 1572-9680
    Keywords: Theobroma cacao ; shade trees ; Erythrina poeppigiana ; Cordia alliodora ; modelling ; organic matter ; nitrogen ; phosphorus ; potassium ; calcium ; magnesium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Models for cycles for organic matter and nutrients element (N, P, K, Ca and Mg) are presented for the agroforestry systems of cacao (Theobroma cacao) withCordia alliodora orErythrina poeppigiana in Turrialba, Costa Rica. For the models, system reserves (soil, humus, vegetation divided into leaves, branches, stems, fine roots, fruits) and transference between compartments (production and decomposition of litter residues) inputs (fertilizer, rainfall) and outputs (harvests) of the system are considered. The implications of the models are discussed in detail. Aspects of net primary production in the systems studied are considered. N fixation is calculated on the basis of balances. Analysis of soil water showed high variations that coincided with rainfall patterns and pruning of theE. poeppigiana.
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    URL: http://dx.doi.org/10.1007/BF02220108
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    Modelling agroforestry systems of cacao (Theobroma cacao) with laurel (Cordia alliodora) and poro (Erythrina poeppigiana) in Costa Rica III. Cycles of organic matter and nutrients (1988)
    Springer
    Agroforestry systems 6 (1988), S. 49-62 
    Details
    ISSN: 1572-9680
    Keywords: Theobroma cacao ; shade trees ; Erythrina poeppigiana ; Cordia alliodora ; modelling ; organic matter ; nitrogen ; phosphorus ; potassium ; calcium ; magnesium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Models for cycles for organic matter and nutrients element (N, P, K, Ca and Mg) are presented for the agroforestry systems of cacao (Theobroma cacao) withCordia alliodora orErythrina poeppigiana in Turrialba, Costa Rica. For the models, system reserves (soil, humus, vegetation divided into leaves, branches, stems, fine roots, fruits) and transference between compartments (production and decomposition of litter residues) inputs (fertilizer, rainfall) and outputs (harvests) of the system are considered. The implications of the models are discussed in detail. Aspects of net primary production in the systems studied are considered. N fixation is calculated on the basis of balances. Analysis of soil water showed high variations that coincided with rainfall patterns and pruning of theE. poeppigiana.
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    URL: http://dx.doi.org/10.1007/BF02344745
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    Effects of pH, Ca and Al on the exudation from clover seedlings of compounds that induce the expression of nodulation genes inRhizobium trifolii (1988)
    Springer
    Plant and soil 109 (1988), S. 37-47 
    Details
    ISSN: 1573-5036
    Keywords: β-galactosidase activity ; calcium ; lac fusion ; nod gene expression ; pH ; Rhizobium trifolii ; seedling exudates ; Trifolium repens ; T. subterraneum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The expression of nodulation genes inR. trifolii is induced by flavone compounds present in clover root exudates. In the present experiments a bioassay with an indicator strain ofR. trifolii, which contained thelacZ gene fromEscherichia coli fused to theR. trifolii nodA gene, was used to measure the level ofnod gene expression inR. trifolii. Compounds that stimulatednodA gene expression were shown to be present in exudates of white clover (Trifolium repens L.) and nine cultivars of subterranan clover (T. subterraneum L.) seedling sgrown at a range of pH between pH 3.0 and pH 8.0. Thenod gene-induction activity of exudates was, however, reduced when seedlings of all clover species were grown at pH〉7.0 and at pH〈4.0 and pH〈5.0 for white clover and subterranean clover respectively. No major differences were apparent in the activity of exudates from seedlings of the various cultivars of subterranean clover.Nod gene-induction activity of exudates was shown to increase markedly with seedling age. The presence of Ca at concentrations up to 10 mM in seedling culture solutions also resulted in marked increases in thenod gene-induction activity of seedling exudates. Increases in activity due to the presence of Ca were most apparent at low pH where between 5 and 10-fold increases were observed for white clover and subterranean clover respectively. Conversely, the presence of Al at concentrations up to 60 μM in seedling culture solutions had no effect on thenod gene-induction activity of seedling exudates. The observations that both low pH and Ca concentrations affected thenod gene-induction activity of seedling exudates suggested that the net presence of stimulatory flavones in root exudates was an important contributing factor to the ‘acid-sensitive’ step in nodule formation.
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    Changes in nutrient distribution in forests and soils of Walker Branch watershed, Tennessee, over an eleven-year period (1988)
    Springer
    Biogeochemistry 5 (1988), S. 275-293 
    Details
    ISSN: 1573-515X
    Keywords: vegetation ; soil pH ; calcium ; magnesium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Changes in vegetation, litter, and soil nutrient content were measured in selected plots on Walker Branch watershed, Tennessee, from 1972–73 to 1982. The watershed has been allowed to revert to forest since 1942, before which it consisted of small subsistence farms and woodland pastures. Changes in Ca status were of particular interest because initial nutrient cycling characterizations indicated that net Ca accumulation in vegetation could have caused large decreases in soil exchangeable Ca2+ within 20 years. Decreases in forest floor and subsoil (45–60 cm) N, exchangeable Ca2+, and Mg2+ content were noted in several plots from 1972 to 1982. Surface soils (0–15 cm) showed either no change or, in some cases (e.g., N and exchangeable K+ in certain plots), increases over the 11-year period. Reductions in forest floor and subsoil exchangeable Ca2+ and exchangeable Mg2+ on cherty, upper slope oak-hickory and chestnut oak forests were most striking. The changes in Ca2+ are thought to be due primarily to high rates of Ca2+ incorporation into woody tissues of oak and hickory species. Reductions in forest floor and subsoil exchangeable Mg2+ could not be accounted for by woody increment; leaching may have played a major role in causing these decreases. Changes in P and exchangeable K+ were variable, with both increases and decreases. There were significant increases in exchangeable Al3+ in both subsoils and surface soils of certain plots, but these were not accompanied by decreases in exchangeable base cations or consistent decreases in pH. Dissolution of interlayer Al from 2:1 clays may be the cause of the exchangeable Al3+ increases. These results suggest a general decline in fertility, especially with regard to Ca and Mg in those forests with low soil Ca and Mg supplies. Monitoring of further changes (if any) in these ecosystems will continue as the currently aggrading forests approach steady state.
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    Mineral Metabolism of Aging Female Rats Fed Various Commercially Available Calcium Supplements or Yogurt (1988)
    Springer
    Pharmaceutical research 5 (1988), S. 501-505 
    Details
    ISSN: 1573-904X
    Keywords: calcium ; supplements ; nephrocalcinosis ; magnesium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The utilization of calcium from commercially available calcium supplements and yogurt and the effects of these calcium supplements on the utilization of other minerals were evaluated. Moderate and high levels (4 and 8 mg Ca/g diet) of calcium from four different sources of dietary calcium (yogurt, calcium phosphate dibasic, calcium magnesium chelate, and oyster shells) were fed to retired female breeder rats. Rats absorbed calcium equally efficiently from all four sources but ingestion of calcium phosphate dibasic tended to cause abnormal accumulation of calcium in kidneys. Ingestion of the calcium magnesium chelate improved calcium retention in bone but depressed the digestibility of the total diet. The elevation of dietary calcium did not affect tissue calcium levels or fecal β-glucuronidase activity but depressed the apparent absorption of phosphorus, increased kidney phosphorus levels, decreased tibia iron levels, and decreased the digestibility of the total diet.
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    URL: http://dx.doi.org/10.1023/A:1015917307961
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    Calcium-induced fusion of didodecylphosphate vesicles: The lamellar to hexagonal II (HII) phase transition (1987)
    Springer
    The journal of membrane biology 95 (1987), S. 255-263 
    Details
    ISSN: 1432-1424
    Keywords: didodecylphosphate ; calcium ; membrane fusion ; lamellar phase ; hexagonal phase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Electron microscopic techniques have been employed to investigate the ability of didodecylphosphate vesicles (diameter approx. 900 Å) to fuse in the presence of Ca2+. As revealed by negative staining, Ca2+ induces extensive fusion and large vesicles with diameters up to 7000 Å are formed. In a processsecondary to fusion, the fused vesicles display a tendency to flatten and are subsequently transformed into extended tubular structures. Freeze-fracture electron microscopy, in conjunction with31P NMR and selected area electron diffraction measurements indicate that the tubes are packed in a hexagonal (HII) array and that the amphiphiles are converted from the lamellar to the hexagonal HII phase. The relationship between membrane fusion and the lamellar-to-hexagonal phase transition is discussed in terms of formation and abundance of transiently stable inverted micellar intermediates at contact regions between two interacting membranes. A model for the conversion of the (vesicular) lamellar into the (tubular) hexagonal HII phase is presented, taking into account the molecular shape of the amphiphile. The relevance of using simple synthetic amphiphiles as models for phospholipid bilayers and complex biomembrane behavior is briefly discussed.
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    URL: http://dx.doi.org/10.1007/BF01869487
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    Calcium transport affinity, ion competition and cholera toxin effects on cytosolic Ca concentration (1987)
    Springer
    The journal of membrane biology 96 (1987), S. 243-249 
    Details
    ISSN: 1432-1424
    Keywords: cholera toxin ; ionophore ; calcium ; brush-border membrane vesicles
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The physiological relevance of an apparent ionophore activity of cholera toxin towards Ca2+ has been examined in several different systems designed to measure affinity, specificity, rates of ion transfer, and effects on intracellular ion concentrations. Half-maximal transfer rates across porcine jejunal brush-border vesicles were obtained at a concentration of 0.20 μM Ca2+. When examined in the presence of competing ions the transfer process was blocked by very low concentrations of La3+ or Cd2+. Sr2+, Ba2+ and Mg2+ were relatively inefficient competitors for Ca2+ transport mediated by cholera toxin. The relative affinities observed would be compatible with a selectivity for Ca2+ transfer at physiological ion concentrations, as well as an inhibition of this ionophore activity by recognized antagonists of cholera toxin such as lanthanum ions. Entry rates of Ca2+ into brush-border vesicles exposed to cholera toxin were large enough to accelerate the collapse of a Ca2+ gradient generated by endogenous Ca, Mg-ATPase activity. The treatment of isolated jejunal enterocytes with cholera toxin caused a significant elevation in cytosolic Ca2+ concentrations as measured by Quin-2 fluorescence. This effect was specifically prevented by prior exposure of the cholera toxin to excess ganglioside GM1. We conclude that cholera toxin has many of the properties required for promoting transmembranes Ca2+ movement in membrane vesicles and appears to be an effective Ca2+ ionophore in isolated mammalian cells.
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    Guayule seedling response to nitrogen fertilizers (1987)
    Springer
    Nutrient cycling in agroecosystems 11 (1987), S. 113-121 
    Details
    ISSN: 1573-0867
    Keywords: ammonium sulfate ; urea ; calcium nitrate ; nitrogen-calcium interaction ; leaching ; subirrigation ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Slow growth and high seedling mortality limit direct seeding establishment of guayule (Parthenium argentatum G.). This study was conducted to assess seedling growth enhancement by the addition of different rates and forms of N fertilizers and Ca salts. Experiments were conducted in a greenhouse with cultivar 593 under both surface and subirrigated conditions using water low in salts (salinity of 0.8 dSm−1, SAR of 5.0 and 10 mg Ca L−1). Under surface-irrigated conditions, seedling height and fresh plant weight increased with N application to the irrigation water to 70 mg L−1. The best seedling growth was observed when (NH4)2SO4 was added in combination with CaCl2 or CaSO4. Progressively less growth was observed by addition of (NH4)2SO4 alone, CO(NH2)2 plus CaSO4, CO(NH2)2 alone and Ca(NO3)2. When seedlings were subirrigated, however, the best growth was observed with Ca(NO3)2. Intermediate growth was obtained with (NH4)2SO4 plus CaSO4 and lowest growth rates with (NH4)2SO4 alone. These differential responses may be explained by the differences in leaching and volatile characteristics of the N forms. Growth enhancement from N and Ca additions increased with time with significant increases 45 days after seeding. Nitrogen application with Ca may be effective amendment in promoting subsequent growth of direct seeded guayule.
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    The variation of element contents in triticale during vegetative growth (1987)
    Springer
    Nutrient cycling in agroecosystems 13 (1987), S. 155-159 
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    ISSN: 1573-0867
    Keywords: triticale ; contents of nitrogen ; phosphorus ; potassium ; calcium ; magnesium ; trace elements ; heavy metals ; stage of growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Description / Table of Contents: Zusammenfassung Es wurden die Schwankungen in den Konzentration von N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, B, Ba, Be, Bi, Sn, Sr, Sb, Ti, Te, V, Se, As und Hg in Triticale unter Feldbedingungen untersucht. Von der Bestockung bis zur Vollreife wurden alle 10 Tage von je 0.5 m2 pro Parzelle Pflanzenproben genommen. In allgemeinen haben die Konzentrationen von Frühjar bis zur Ernte abgenommen. Der elementengehalt in Triticale war demjenigen der übrigen Getreidearten verschieden, aber der Trend der Änderungen war ähnlich.
    Notes: Abstract The variation of N, P, K, Ca, Mg, Fe, Mn, Zn, Cu, B, Ba, Be, Bi, Sn, Sr, Sb, Ti, Te, V, Se, As and Hg concentrations was studied under field conditions in triticale. The samples were collected every 10 days from tillering to full ripening stage using plant material from 0.5 m2 per plot. The concentrations generally decreased from early growth to harvest. The elemental concentrations in triticale differed from the other cereals, but the variation's trend was similar.
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    Biological effects of lithium: Experimental analysis in plant cytokinesis (1987)
    Springer
    Cellular and molecular life sciences 43 (1987), S. 1025-1027 
    Details
    ISSN: 1420-9071
    Keywords: Plant cytokinesis ; lithium ; caffeine ; calcium ; magnesium ; sodium and potassium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The biological effects of lithium ions have been studied, using plant cytokinesis in onion root meristems as the experimental model. Lithium induces binucleate cells by inhibiting cell plate formation. Moreover, lithium and caffeine have additive effects on the induction of binucleate cells. Na+, K+, Ca++ and Mg++ antagonize lithium-induced inhibition of cytokinesis.
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    Effects of calcium on the gramicidin A single channel in phosphatidylserine membranes (1987)
    Springer
    European biophysics journal 14 (1987), S. 369-374 
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    ISSN: 1432-1017
    Keywords: Single-channels ; model membranes ; gramicidin ; surface potential ; phosphatidylserine ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract In phosphatidylserine membranes the decrease in the conductance of the gramicidin A single channel caused by calcium is attributed to a reduction of surface potential and to a direct blocking of the pore (Apell et al. 1979). The aim of this paper is to make a, quantitative evaluation of these two effects. We recorded the conductance of gramicidin single channels in 100 mM KCl in the presence of different amounts of CaCl2, MgCl2 or TEACl. The ionic activities at the channel mouth were calculated using the Gouy-Chapman-Stern theory. Our experiments showed that even when the K+ activity at the channel mouth was estimated to be the same, the single channel conductance was lower if divalent cations were present. This effect is attributed to a blocking action of these ions.
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    Neutron scattering by calf lens cytoplasm (1987)
    Springer
    European biophysics journal 14 (1987), S. 441-447 
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    ISSN: 1432-1017
    Keywords: Neutron scattering ; lens ; cataract ; calcium ; cold cataract
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Physics
    Notes: Abstract Small angle neutron scattering (SANS) was used to compare two models of cataracts: the cold cataract induced in the lens nucleus cytoplasm by lowering the temperature and the opacification induced by calcium in the lens cortex cytoplasm. In both cases opacified cytoplasms display additional scattering at low angles as compared to their clear controls. An analysis of this additional scattering provides quantitative information concerning the size distribution, the number and contrast of the scatterers responsible for lens opacification. The scatterers of cold cataract and of calcium—induced opacification not only have, as shown elsewhere, a different composition but are also found to display completely different sizes (in the thousand Å range for cold-cataract, in the hundred Å range for calcium—induced opacification). These results illustrate the diversity of scatterer types which are able to cause comparable lens opacities.
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    Regulation of exocytosis in electrically permeabilized insulin-secreting cells. Evidence for Ca2+ dependent and independent secretion (1987)
    Springer
    Bioscience reports 7 (1987), S. 443-454 
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    ISSN: 1573-4935
    Keywords: calcium ; exocytosis ; insulin secretion ; permeabilized cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The regulation of insulin secretion from RINm5F cells exposed to high voltage discharge has been investigated. Electron microscopy revealed that the overall structure of the cells was preserved after permeabilization. In this preparation insulin release was stimulated by Ca2+ (EC50=2.4 μM). The stable GTP analogue GTPγS enhanced secretion both at intermediate (nano- to micromolar) and vanishingly low (〈10 pM) Ca2+ concentrations. At optimal Ca2+ (10 μM) the effect of GTPγS was greatly reduced. We investigated whether the secretory response to GTP analogues was mediated by any of three enzyme systems regulated by GTP-binding proteins, i.e. generation of cyclic AMP by adenylate cyclase, of diacylglycerol by phospholipase C and of arachidonic acid by phospholipase A2. The involvement of these messenger systems could be excluded as (i) cyclic AMP only had minor, Ca2+ dependent effects, (ii) phospholipase C was not activated in the absence of Ca2+ and insulin secretion due to the phorbol ester TPA displayed a different Ca2+ dependency, (iii) arachidonic acid did not elicit Ca2+ independent insulin secretion. These results, taken together with the finding that insulin secretion due to Ca2+ or TPA is attenuated by the inhibitory guanine nucleotide GDPβS, suggest the existence of a regulatory site in exocytosis which is sensitive to guanine nucleotides.
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    Calcium and diacylglycerol control of secretion (1987)
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    Bioscience reports 7 (1987), S. 355-367 
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    ISSN: 1573-4935
    Keywords: calcium ; diacylglycerol ; exocytosis ; secretion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Measurements of intracellular Ca2+ in adrenal medullary cells suggest that a transient rise in Ca2+ leads to a transient secretory response, the rise in Ca2+ being brought about by an influx through voltage-sensitive Ca channels which subsequently inactivate. The level of Ca2+ observed is much smaller than the Ca2+ needed to trigger secretion when introduced directly into the cell. The discrepancy is removed by the presence of diacylglycerot, which increases the sensitivity of the secretory process to Ca2+. The site of action of Ca2+ and diacylglycerol is probably protein kinase C, and tile different secretory responses to increases of Ca2+ and diacylglycerol can be modelled in terms of a preferential order of binding of these two substrates to the enzyme. ATP is needed for secretion: one role is possibly to confer stability to the secretory apparatus; another may involve phosphorylation of some key protein. The kinetics of secretion suggest that if Ca2+ regulates phosphorylation or dephosphorylation, then it is therate of change of phosphorylation that controls secretion rather than theextent of phosphorylation or dephosphorylation. Guanine nucleotide-binding proteins may play a role not only at the level of signal transduction coupling, but also at or near the site of exocytosis, and the mechanism by which some Botulinum toxins inhibit secretion may be associated with these proteins.
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    How calcium may cause exocytosis in sea urchin eggs (1987)
    Springer
    Bioscience reports 7 (1987), S. 383-397 
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    ISSN: 1573-4935
    Keywords: calcium ; eggs ; exocytosis ; sea urchin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The process of secretory granule-plasma membrane fusion can be studied in sea urchin eggs. Micromolar calcium concentrations are all that is required to bring about exocytosisin vitro. I discuss recent experiments with sea urchin eggs that concentrate on the biophysical aspects of granule-membrane fusion. The backbone of biological membranes is the lipid bilayer. Sea urchin egg membrane lipids have negatively charged head groups that give rise to an electrical potential at the bilayer-water interface. We have found that this surface potential can affect the calcium required for exocytosis. Effects on the surface potential may also explain why drugs like trifluoperazine and tetracaine inhibit exocytosis: they absorb to the bilayer and reduce the surface potential. The membrane lipids may also be crucial to the formation of the exocytotic pore through which the secretory granule contents are released. We have measured calcium-induced production of the lipid, diacylglycerol. This lipid can induce a phase transition that will promote fusion of apposed lipid bilayers. The process of exocytosis involves the secretory granule core as well as the lipids of the membrane. The osmotic properties of the granule contents lead to swelling of the granule during exocytosis. Swelling promotes the dispersal of the contents as they are extruded through the exocytotic pore. The movements of water and ions during exocytosis may also stabilize the transient fusion intermediate and consolidate the exocytotic pore as fusion occurs.
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    The molecular and biochemical basis of cystic fibrosis (1987)
    Springer
    Bioscience reports 7 (1987), S. 167-185 
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    ISSN: 1573-4935
    Keywords: cystic fibrosis ; exocrine ; autonomic ; cyclic AMP ; calcium ; chloride ; epithelial
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
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    URL: http://dx.doi.org/10.1007/BF01124787
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    Electrophysiological evidence suggests a defective Ca2+ control mechanism in a newParamecium mutant (1987)
    Springer
    The journal of membrane biology 98 (1987), S. 275-283 
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    ISSN: 1432-1424
    Keywords: Paramecium ; calcium ; cilia ; mutants ; Ca2+ pump ; Ca2+ buffering ; ion channels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A new mutant ofParamecium tetraurelia, k-shyA, was characterized behaviorally and electrophysiologically. The mutant cell exhibited prolonged backward swimming episodes in response to depolarizing conditions. Electrophysiological comparison of k-shyA with wild type cells under voltage clamp revealed that the properties of three Ca2+-regulated currents were altered in the mutant. (i) The voltage-dependent Ca2+ current recovered from Ca2+-dependent inactivation two- to 10-fold more slowly than wild type. Ca2+ current amplitudes were also reduced in the mutant, but could be restored by EGTA injection. (ii) The decay of the Ca2+-dependent K+ tail current was slower in the mutant. (iii) The decay of the Ca2+-dependent Na+ tail current was also slower in the mutant. All other membrane properties studied, including the resting membrane potential and resistance and the voltage-sensitive K+ currents, were normal in k-shyA. Considered together, these observations are consistent with a defect in the ability of k-shyA to reduce the free intracellular Ca2+ concentration following stimulation. The possible targets of the genetic lesion and alternative explanations are discussed. The k-shy mutants may provide a useful tool for molecular and physiological analyses of the regulation of Ca2+ metabolism inParamecium.
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    Na+/K+/Cl− cotransport in cultured vascular smooth muscle cells: Stimulation by angiotensin II and calcium ionophores, inhibition by cyclic AMP and calmodulin antagonists (1987)
    Springer
    The journal of membrane biology 99 (1987), S. 51-63 
    Details
    ISSN: 1432-1424
    Keywords: endothelial cells ; Na+/K+/Cl− cotransport ; cyclic AMP ; phenothiazines ; calcium ; angiotensin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The specific activity of the Na+/K+/Cl− cotransporter was assayed by measuring the initial rates of furosemide-inhibitable86Rb+ influx and efflux. The presence of all three ions in the external medium was essential for cotransport activity. In cultured smooth muscle cells furosemide and bumetanide inhibited influx by 50% at 5 and 0.2 μm, respectively. The dependence of furosemide-inhibitable86Rb+ influx on external Na+ and K+ was hyperbolic with apparentK m values of 46 and 4mm, respectively. The dependence on Cl− was sigmoidal. Assuming a stoichiometry of 1∶1∶2 for Na+/K+/Cl−, aK m of 78mm was obtained for Cl−. In quiescent smooth muscle cells cotransport activity was approximately equal to Na+ pump activity with each pathway accounting for 30% of total86Rb+ influx. Growing muscle cells had approximately 3 times higher cotransport activity than quiescent ones. Na+ pump activity was not significantly different in the gorwing and quiescent cultures. Angiotensin II (ANG) stimulated cotransport activity as did two calcium-transporting ionophores, A23187 and ionomycin. The removal of external Ca2+ prevented A23187, but not ANG, from stimulating the cotransporter. Calmodulin antagonists selectively inhibited86Rb+ influx via the cotransporter. Beta-adrenoreceptor stimulation with isoproterenol, like other treatments which increase cAMP, inhibited cotransport activity. Cultured porcine endothelial cells had 3 times higher cotransport activity than growing muscle cells. Calmodulin antagonists inhibited cotransport activity, but agents which increase cAMP or calcium had no effect on cotransport activity in the endothelial cells.
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    Effect of a calcium channel blocker on pituitary luteinizing hormone secretion in intact and castrated male and female rats (1987)
    Springer
    Bulletin of experimental biology and medicine 103 (1987), S. 400-402 
    Details
    ISSN: 1573-8221
    Keywords: luteinizing hormone ; sex steroids ; calcium ; verapamil
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00840576
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    Genetic analysis of inheritance of rates of Na+, K+-cotransport, calcium concentration in erythrocytes, and blood pressure of F2 hybrids of spontaneously hypertensive and normotensive rats (1987)
    Springer
    Bulletin of experimental biology and medicine 103 (1987), S. 518-520 
    Details
    ISSN: 1573-8221
    Keywords: calcium ; spontaneous hypertension ; orthovanadate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00842486
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    Antioxidant-induced calcium transport in biological membranes (1987)
    Springer
    Bulletin of experimental biology and medicine 104 (1987), S. 1220-1223 
    Details
    ISSN: 1573-8221
    Keywords: biological membranes ; antioxidant ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00841997
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    The dual effector system for exocytosis in mast cells: Obligatory requirement for both Ca2+ and GTP (1987)
    Springer
    Bioscience reports 7 (1987), S. 369-381 
    Details
    ISSN: 1573-4935
    Keywords: stimulus-secretion coupling ; G-proteins ; mast cells ; calcium ; permeabilised cells ; streptolysin-O ; exocytosis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The secretory process is a coordinated cellular response, initiated by occupation of surface receptors and comprising an ordered sequence of biochemical steps subject to multiple controls. Conceptually we can divide the sequence into two main sections comprising early, receptor-mediated events leading to generation of intracellular second messengers, and later events leading to membrane fusion and exocytosis. With the discovery that occupation of Ca2+ mobilising receptors leads to activation of polyphosphoinositide phosphodiesterase (PPI-pde) through the mediation of a G-protein (Gp), all the early events can be ascribed to the plasma membrane. Investigation of the exocytotic stage of secretion has been simplified by the use of permeabilised cells in which the composition of the cytosol can be precisely controlled. We have used streptolysin-O, a bacterial cytolysin which generates protein-sized pores in the plasma membrane, to investigate the exocytotic mechanism of rat mast cells. We find that in addition to the activation of PPI-dpe, GTP also acts in concert with Ca2+ at, or close to, the exocytotic site. Exocytosis can occur after substantial depletion of cytosol lactate dehydrogenase and 3-phosphoglycerate kinase indicating that soluble cytosol proteins are unlikely to play any role. There is no absolute requirement for ATP or phosphorylating nucleotide in exocytosis though when present the effective affinities of the two obligatory effectors (i.e. Ca2+ and GTP) are substantially enhanced.
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    Effect of calcium and F-actin on the rate of SH2 modification in skeletal myosin (1987)
    Springer
    Bioscience reports 7 (1987), S. 543-551 
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    ISSN: 1573-4935
    Keywords: calcium ; F-actin ; myosin ; SH2 region
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The rate constant of modification of a specific thiol group, SH2, with N-ethylmaleimide (NEM) has been used to estimate the conformational change in the local area containing SH2 (SH2 region) of skeletal myosin as a structural probe. The rate of Mg2+-ATP-induced SH2 modification of subfragment-1 (S-l) isozymes was regulated by Ca2+ in the pCa range below 6.4 and was not regulated in the pCa range above 6.4. No substantial difference between S-1 containing alkali light chain, A1, (S-1(A1)) and S-1 containing alkali light chain, A2, (S-1(A2)) was observed in the Ca2+-dependent rate of SH2 modification. Due to the presence of this Ca2+ regulation in myosin (absence in S-1 isozymes) in the pCa range above 6.4, absence of 5,5′-dithiobis-(2-nitrobenzoic acid) (DTNB) light chain in S-1 isozymes, and high affinity of Ca2+ for DTNB light chain, this Ca2+ regulation in the pCa range above 6.4 is possibly related to the Ca2+ binding to DTNB light chain. F-Actin, which is entirely free from tropomyosin and troponin, enhanced the rate of Mg2+-ATP-induced SH2 modification of S-1 isozymes equally and of myosin, and reduced the Ca2+ sensitivity with an increase in F-actin concentration.
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    Nutrient concentrations in litterfall from some western conifers with special reference to calcium (1987)
    Springer
    Plant and soil 102 (1987), S. 223-227 
    Details
    ISSN: 1573-5036
    Keywords: calcium ; cupressaceae ; leaf litter ; litterfall ; nutrients ; pinaceae ; taxodiaceae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Foliar litterfall nutrient concentrations were analysed for selected members of Taxodiaceae and Cupressaceae families andPseudotsuga menziesii for two arboreta in western Oregon and Washington. Nutrient results between arboreta show similar concentrations with the exception of magnesium, which may be the result of historical land use. Nutrient concentrations between species vary considerably.Pseudotsuga menziesii is particularly distinctive from the Cupressaceae and Taxodiaceae by retaining large amounts of phosphorus and potassium. Taxodiaceae is distinctive by high concentration of Mg while Cupressaceae retains calcium, especiallyChamaecyparis nootkatensis. Results suggest that all members of Taxodiaceae and Cupressaceae retain considerably more Ca than Pinaceae in foliar litter.
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    Effects of intermittent waterlogging on the mineral nutrition of cotton (1987)
    Springer
    Plant and soil 101 (1987), S. 211-221 
    Details
    ISSN: 1573-5036
    Keywords: aeration ; calcium ; cotton ; flooding ; magnesium ; manganese ; phosphorus ; potassium ; sodium chloride ; waterlogging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract A field experiment was conducted to investigate the effects of intermittent waterlogging on the nutrient status of cotton (Gossypium hirsutum cv. Deltapine 61). The crop was grown in a sloping plot of soil in which a gradient of water-table depth ranging from 0.04m above to 0.60m below the soil surface was established during two periods of waterlogging in mid summer and early autumn. The first waterlogging lasted 8 days; the second lasted 16 days. Dry matter increases were less for severely waterlogged plants than for plants with well-aerated root systems during the first flooding, but the increases were similar during the second. Waterlogging impaired uptake of most nutrients by young plants in the first flooding, but had much less effect on nutrient uptake by older plants in the second. Waterlogging consistently reduced concentrations of P and K in the petioles and laminae of young fully-expanded leaves, and severely waterlogged plants were deficient in these nutrients by the end of the first flooding. Mn did not accumulate to toxic levels in waterlogged plants. During each flooding, waterlogged plants gained in total content of all nutrients studied, but the gains of each nutrient, except for Na, were proportionally smaller than for well-aerated plants. Fluxes of K-, Cl- and HPO4- ions in xylem sap exuded from stumps of detopped plants which had been waterlogged were lower than those from plants with well-aerated root systems. Seed cotton yields and concentrations of nutrients in mature bolls were not affected by the two periods of waterlogging. It is concluded that although intermittent waterlogging induced nutrient stress in cotton plants, especially for P and K in young plants before flowering, they recovered with no detrimental effect upon yield.
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    Effects of switches in nutrient levels during the life cycle of spring wheat (1987)
    Springer
    Plant and soil 103 (1987), S. 199-204 
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    ISSN: 1573-5036
    Keywords: calcium ; growth ; influx ; iron ; magnesium ; nutrient solution ; potassium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Accumulation of cations in roots and shoots and influx of K+(86Rb+) and Ca2+(45Ca2+) into the roots were investigated in spring wheat (Triticum aestivum L. cv. Svenno). Plants were sampled at four main developmental stages: tillering, shooting, heading and grain filling. The effects of switches between a high and a low supply of nutrients were characterized. Growth of the shoots and roots was affected by the switches. A high supply of nutrients at the seedling stage and towards tillering supported a high growth rate, while a further high supply of nutrients increased vegetative growth and delayed grain filling. An early high supply of nutrients followed by a low supply at shooting, heading and grain filling accelerated root growth and growth of the main culm. Switches of the mineral supply gave only small changes in concentration of Mg in the plants. Generally, the K+(86Rb+) influx into the roots decreased during ontogenesis, while Ca2+(45Ca2+) influx increased more or less independent of the switches between nutrients levels.
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    Responses of pyriform cortex neurons to excitatory amino acids: Voltage dependence, conductance changes, and effects of divalent cations (1987)
    Springer
    Cellular and molecular neurobiology 7 (1987), S. 73-90 
    Details
    ISSN: 1573-6830
    Keywords: pyriform cortex ; kainate ; quisqualate ; N-methyl aspartate ; ion channels ; zinc ; cobalt ; calcium ; magnesium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. The actions of ionophoretically appliedN-methyl aspartate (NMA), quisqualate, and kainate, thought to activate three different types of excitatory amino acid receptors, were studied on pyramidal neurons of the rat pyriform cortex, maintained in an isolated, submerged, and perfused brain slice. Intracellular recordings were made with either K acetate or CsCl electrodes. 2. In most neurons all three agonists elicited monophasic responses which could be evoked at 20-sec intervals. Some neurons showed biphasic responses, most commonly to kainate but, on occasion, also for quisqualate. The slower component appeared to be correlated with excitotoxicity and, consequently, was difficult to study. As a result the kainate responses studied were from neurons selected for having a single component. 3. In neurons selected for having a linear current-voltage relationship or neurons loaded with Cs to suppress K conductance and linearize the current-voltage relationship, the average changes in resistance recorded during ionophoretic responses at resting potential were as follows: NMA, 131.2 ± 6.7% of control; kainate, 104.7 ± 5.8% of control; and quisqualate, 92.8 ± 2.8% of control. The magnitude and direction of the conductance change were very reproducible in any one neuron, but especially for kainate some cells showed clear conductance increases, while others showed clear conductance decreases. 4. Using CsCl electrodes it was possible to reduce K+ conductance and depolarize the neurons over a wider range. By passing depolarizing current it was possible to reverse the responses. The response to all three agonists reversed at the same depolarized potential. This observation indicates that while there are differences in the ionic channels associated with the three agonists at resting potential, the channels have similar properties at more depolarized potentials. 5. Responses to all three agonists were influenced by the concentrations of divalent cations in the perfusion medium. The NMA responses were most sensitive to Mg, increasing in amplitude in the absence of Mg and being depressed by Mg elevation. All responses were sensitive to Ca, with discharges being greatly increased by low Ca and depressed by high Ca. The kainate response was most sensitive to Ca concentration changes. 6. Unlike reports from other preparations the apparent conductance decreases to NMA were not altered by the perfusion of solutions with either no added Mg or no added Ca. 7. The NMA response was very much reduced in either Co (1–2mM) or Zn (100–200µM). In contrast, the quisqualate response was relatively insensitive to Co but was consistently increased in the presence of Zn. The kainate response was not consistently affected by either, although there was some variation in individual experiments. 8. These results are consistent with the hypothesis that there are at least three distinct types of receptors for the excitatory amino acids in pyriform cortex and that these receptors are associated with three distinct ionic channels. The channels have many similar properties but possibly differ in divalent cation binding sites which regulate conductance to other ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00734991
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  • 97
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    Action of cyclosporine on mitochondrial calcium fluxes (1987)
    Springer
    Journal of bioenergetics and biomembranes 19 (1987), S. 297-303 
    Details
    ISSN: 1573-6881
    Keywords: Cyclosporine ; calcium ; mitochondria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Cyclosporine (Cys A) is a potent immunosuppressor used to reduce rejection in transplantation surgery. We studied its action upon mitochondrial functions: oxidative phosphorylation and Ca2+ movements through mitochondrial membrane. We show that Cys A exhibits an inhibitory effect upon mitochondrial respiration. This result is in good agreement with previous works and may be correlated with Cys A toxicity. The action of cyclosporine on calcium fluxes is more pronounced. Indeed it blocks mitochondrial calcium efflux and allows mitochondria to accumulate a large amount of calcium. If this effect occurs in the cell, it would induce a Ca2+ decrease in cytosol. This action might be correlated with the inhibitory effect of Cys A upon the mitogenic stimulation of T lymphocytes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00762419
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  • 98
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    The mechanism of lead-induced mitochondrial Ca2+ efflux (1987)
    Springer
    Journal of bioenergetics and biomembranes 19 (1987), S. 285-295 
    Details
    ISSN: 1573-6881
    Keywords: Mitochondria ; lead ; calcium ; NAD(P)H oxidation ; calcium transport ; mitochondrial calcium ; pyridine nucleotide oxidation ; kidney mitochondria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Addition of Pb2+ to rat kidney mitochondria is followed by induction of several reactions: inhibition of Ca2+ uptake, collapse of the transmembrane potential, oxidation of pyridine nucleotides, and a fast release of accumulated Ca2+. When the incubation media are supplemented with ruthenium red, the effect of Pb2+ on NAD(P)H oxidation, membrane ΔΨ, and Ca2+ release are not prevented if malate-glutamate are the oxidizing substrates; however, the latter two lead-induced reactions are prevented by ruthenium red if succinate is the electron donor. It is proposed that in mitochondria oxidizing NAD-dependent substrates, Pb2+ induces Ca2+ release by promoting NAD(P)H oxidation and a parallel drop in ΔΨ due to its binding to thiol groups, located in the cytosol side of the inner membrane. In addition, it is proposed that with succinate as substrate, the Ca2+-releasing effect of lead is due to the collapse of the transmembrane potential as a consequence of the uptake of Pb2+ through the calcium uniporter, since such effect is ruthenium red sensitive.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00762418
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  • 99
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    Inhibition of the Na+/Ca2+ antiport of heart mitochondria by diethylpyrocarbonate (1987)
    Springer
    Journal of bioenergetics and biomembranes 19 (1987), S. 515-524 
    Details
    ISSN: 1573-6881
    Keywords: Mitochondria ; diethylpyrocarbonate ; heart ; inhibition ; sodium ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Diethylpyrocarbonate inhibits Na+/Ca2+ antiport activity in isolated heart mitochondria. The inhibition is time-dependent with maximum activity developed after 5 min at 25°C. The reaction of diethylpyrocarbonate with the mitochondrial membrane is biphasic with 25–30 nmol mg−1 reacting rapidly and an additional 30 nmol mg−1 taken up slowly over a 30-min incubation. Inhibition of mitochondrial Na+/Ca2+ antiport by diethylpyrocarbonate decreases theV max of the reaction, and the inhibition cannot be reversed by washing the mitochondria or addition of excess histidine. The inhibition occurs at levels of inhibitor that have little or no effect on Ca2+ uptake, Na+/H+ antiport, or succinate respiration. A portion of the Na+-dependent efflux of Ca2+ is insensitive to diethylpyrocarbonate and this component is abolished by diltiazem. The mechanism by which diethylpyrocarbonate inactivates Na+/Ca2+ antiport is still uncertain, but may involve the modification of an unprotonated histidine residue in the transporter.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00770034
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  • 100
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    Control of mitochondrial Ca2+ retention by ADP-stimulated glutamic dehydrogenase (1987)
    Springer
    Journal of bioenergetics and biomembranes 19 (1987), S. 571-580 
    Details
    ISSN: 1573-6881
    Keywords: Mitochondria ; calcium ; mitochondrial Ca2+ transport ; adenine nucleotides ; glutamic dehydrogenase ; kidney mitochondria ; ADP-stimulated glutamic dehydrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The protective effect of ADP on unspecific Ca2+ release and collapse of the transmembrane potential was analyzed in mitochondria from kidneys of rats. The presence of ADP in the incubation mixture prevents Ca2+ leakage and collapse of δω in sucrose-containing medium, but fails to do so in KCl medium. The effect of the adenine nucleotide in sucrose media correlates with an increase in the level of reduced pyridine nucleotides; the increase was due to a stimulatory effect on the activity of glutamic dehydrogenase. It also was observed that in KCl media, in the presence and in the absence of ADP the rate of NADH oxidation through the respiratory chain was higher than in sucrose; in this latter medium a high level of reduced pyridine nucleotides was found, in comparison to KCl media. It is proposed that the role of ADP is to increase glutamic dehydrogenase activity and in consequence to provoke a higher rate of formation of NADH which in turn controls Ca2+ release.
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    URL: http://dx.doi.org/10.1007/BF00770038
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