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  • calcium  (147)
  • Springer  (147)
  • 2015-2019
  • 1985-1989  (147)
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  • 1
    Electronic Resource
    Electronic Resource
    Mechanical and biochemical characterization of the contraction elicited by a calcium-independent myosin light chain kinase in chemically skinned smooth muscle (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 1002-1006 
    Details
    ISSN: 1420-9071
    Keywords: Smooth muscle ; calcium ; myosin light chain kinase ; regulation of contraction ; ATPase ; mechanics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The contraction induced by a Ca2+-independent myosin light chain kinase (MLCK-) was characterized in terms of isometric force (Fo), immediate elastic recoil (SE), unloaded shortening velocity (Vus), shortening under a constant load and ATPase activity of chemically skinned smooth muscle preparations. These parameters were compared to those measured in a Ca2+-induced contraction to assess the nature of cross bridge interaction in the MLCK-induced contraction. Fo developed in chicken gizzard fibers as well as SE were similar in contractions elicited by either agent. Vus in the contraction induced by MLCK-(0.36 mg/ml) was similar though averaged 39.3±8.9% less than Vus induced by Ca2+ (1.6x10−6M) in the control fibers. Addition of Ca2+ (1.6x10−6M) to a contraction induced by MLCK-resulted in small increases in both Fo and Vus. Shortening under a constant load was similar for both types of contractions. The contraction induced by MLCK-was accompanied by an increased rate of ATP hydrolysis. The MLCK-induced contraction is thus kinetically similar though not identical to a contraction induced by Ca2+. We conclude that with respect to actin-myosin interaction, MLCK- and Ca2+-induced contractions are similar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952121
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  • 2
    Electronic Resource
    Electronic Resource
    Failure of calcium to stimulate Na, K-ATPase in the presence of EDTA (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 1048-1051 
    Details
    ISSN: 1420-9071
    Keywords: Na, K-ATPase ; calcium ; calmodulin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The effect of calcium on Na, K-ATPase activity of rat brain homogenates and its modification by the chelating agent EDTA has been investigated. In the absence of EDTA, free calcium (approximately 10−6mol/l) stimulates Na,K-ATPase activity; in the presence of EDTA the same concentration of free calcium is without effect on the enzyme. In the absence of EDTA the stimulation by calcium of Na,-K-ATPase activity is enhanced by the additional presence of calmodulin but in the presence of EDTA, even when calmodulin is added to excess, calcium still fails to stimulate the enzyme. The possibility that EDTA interferes with an interaction between a calcium-calmodulin complex and Na,K-ATPase is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952137
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  • 3
    Electronic Resource
    Electronic Resource
    Increase in cellular cyclic GMP level by potassium stimulation and its relation to ciliary orientation inParamecium (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 62-64 
    Details
    ISSN: 1420-9071
    Keywords: Cyclic GMP ; calcium ; Paramecium ; triton-extracted model ; ciliary reversal ; excitable membrane
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Physiological roles of cyclic GMP in the control of ciliary movement inParamecium caudatum were investigated. We found that 1) an increase in cellular cyclic GMP level was observed in association with recovery from the ciliary reversal produced by K stimulation, and 2) the presence of cyclic GMP inhibited the Ca-induced ciliary reversal in triton-extracted models. These results suggest that cyclic GMP plays a key role in the control of the Ca-mediated ciliary reversal mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01975897
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  • 4
    Electronic Resource
    Electronic Resource
    Modulation of calcium sensitivity in guinea pig taenia coli: skinned fiber studies (1985)
    Springer
    Cellular and molecular life sciences 41 (1985), S. 997-1001 
    Details
    ISSN: 1420-9071
    Keywords: Myosin light chain kinase ; calcium ; c-AMP ; calmodulin ; smooth muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952120
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  • 5
    Electronic Resource
    Electronic Resource
    The effects of acid deposition on benthic animals in lakes and streams (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 471-486 
    Details
    ISSN: 1420-9071
    Keywords: Acidification ; benthic animals ; calcium ; invertebrates ; lakes ; pH ; streams ; fresh water
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01946685
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of water acidification on the distribution pattern and the reproductive success of amphibians (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 495-503 
    Details
    ISSN: 1420-9071
    Keywords: Acidication ; pH ; calcium ; (heavy) metals ; ammonium ; amphibians ; development of eggs ; hatching percentage ; mortality of larvae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Nine amphibian species were encountered in poorly buffered waters of The Netherlands (alkalinity ≦1 meq·l−1). These soft water systems are highly sensitive to acidifying precipitation. The number of species as well as the percentage of waters which harbour amphibian populations are strongly reduced in the extremely acid pH-class $$(\bar pH〈 4.0)$$ . The reproductive success of amphibians is negatively affected by low pH. The eggs become heavily infested with fungi (Saprolegniaceae). In acidifying systems many physico-chemical parameters are significantly correlated with the pH of the water. Strongly acidified waters are characterized by low alkalinity, conductivity and ionic content but high acidity and high concentrations of (heavy) metals and ammonium and a high relative sulphate concentration. Culture experiments with eggs and larvae ofRana arvalis. Rana ‘esculenta’, Rana temporaria andBufo bufo show that apart from the pH, elevated aluminium, cadmium and ammonium contents may also affect the reproductive success of amphibians.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01946687
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  • 7
    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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  • 8
    Electronic Resource
    Electronic Resource
    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 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01952189
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  • 9
    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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  • 10
    Electronic Resource
    Electronic Resource
    Ca2+-activated K+ channels in the apical membrane ofNecturus choroid plexus (1988)
    Springer
    The journal of membrane biology 105 (1988), S. 207-219 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870998
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  • 11
    Electronic Resource
    Electronic Resource
    Ca2+-activated K+ currents inNecturus choroid plexus (1988)
    Springer
    The journal of membrane biology 105 (1988), S. 221-231 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870999
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  • 12
    Electronic Resource
    Electronic Resource
    Ca2+ buffer sites in intact bovine rod outer segments: Introduction to a novel optical probe to measure ionic permeabilities in suspensions of small particles (1985)
    Springer
    The journal of membrane biology 88 (1985), S. 249-262 
    Details
    ISSN: 1432-1424
    Keywords: calcium ; rod photoreceptors ; surface potentials
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The nature of the Ca2+ buffer sites in intact rod outer segments isolated from bovine retinas (ROS) was investigated. The predominant Ca2+ buffer in intact ROS was found to be negatively charged groups confined to the surface of the disk membranes. Accordingly, Ca2+ buffering in ROS was strongly influenced by the electrostatic surface potential. The concentration of Ca2+ buffer sites was about 30mm, 80% of which were located at the membrane surface in the intradiskal space. A comparison with observations in model systems suggests that phosphatidylserine is the major Ca2+ buffer site in ROS. Protons and alkali cations could replace Ca2+ as mobile counterions for the fixed negatively charged groups. At physiological ionic strength, the total number of these diffusible, but osmotically inactive, counterions was as large as the number of osmotically active cations in ROS. The surface potential is dependent on the concentration of cations in ROS and can be measured with the optical dye neutral red. Addition of cations to the external solution led to the release of the internally bound dye as the cations crossed the outer membrane. The chemical and spectral properties of the dye enable its use as a real-time indicator of cation transport across the outer envelope of small particles in suspension. In this study, the dye method is illustrated by the use of well-defined ionophores in intact ROS and in liposomes. In the companion paper this method is used to describe the cation permeabilities native to ROS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871089
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  • 13
    Electronic Resource
    Electronic Resource
    The role of phosphoinositiees in signal transduction (1986)
    Springer
    The journal of membrane biology 89 (1986), S. 193-210 
    Details
    ISSN: 1432-1424
    Keywords: phosphoinositides ; phosphatidylinositol ; inositol-1,4,5-trisphosphate ; diacylglycerol ; arachidonic acid ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870664
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  • 14
    Electronic Resource
    Electronic Resource
    Ionic and permeability requirements for exocytosis in vitro in sea urchin eggs (1988)
    Springer
    The journal of membrane biology 101 (1988), S. 199-207 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01872835
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  • 15
    Electronic Resource
    Electronic Resource
    Effects of membrane potential on sodium-dependent calcium uptake by sarcolemma-enriched preparations from canine ventricle (1985)
    Springer
    The journal of membrane biology 84 (1985), S. 207-219 
    Details
    ISSN: 1432-1424
    Keywords: sodium/calcium exchange ; excitation-contraction coupling ; sarcolemma ; membrane potential ; sodium ; calcium ; heart
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The effect of membrane potential on sodium-dependent calcium uptake by vesicles in an isolated cardiac sarcolemma preparation was examined. Initial time course studies showed that the reaction deviated from initial velocity conditions within minutes. This appeared to be due, in part, to loss of the sodium gradient. Assays carried out to 10 sec revealed a linear component of uptake (2 to 10 sec) and a faster component (complete by 2 sec). The latter was eliminated by loading the preparation with ethyleneglycol-bis-(β-aminoethyl ether)N,N′-tetraacetic acid (EGTA). This maneuver did not affect the slow component, and subsequent studies used preparations containing EGTA. Potassium Nernst potentials (E K), established by potassium gradients in the presence of valinomycin, were varied from −100 to +30 mV by changing [K+] o from 1.18 to 153.7mM ([K+] i =50mM). The initial velocity of sodium-dependent calcium uptake was stimulated twofold by changingE K from −100 to 0 mV and another twofold by raisingE K from 0 to +30 mV. For the total range ofE K and [K+] o , 32 to 36% of the increase appeared to reflect stimulation by extravesicular potassium. The remainder appeared to be due to membrane potential. The profile of sodium-dependent calcium uptake versusE K suggested that calcium influx through electrogenic sodium/calcium exchange may be much more affected by the positive region of the cardiac action potential than by the negative region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871384
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  • 16
    Electronic Resource
    Electronic Resource
    Electric pulse-induced fusion of mouse lymphoma cells: Roles of divalent cations and membrane lipid domains (1985)
    Springer
    The journal of membrane biology 85 (1985), S. 269-280 
    Details
    ISSN: 1432-1424
    Keywords: cell fusion ; electrofusion ; dielectrophoresis ; calcium ; magnesium ; membrane lipid ; lymphoma cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Mouse leukemic lymphoblasts (L5178Y) brought into close contact by dielectrophoresis underwent cell fusion following the application of electrical pulses in the presence of electrolytes. The electrically fused cells became spherical after switching off the dielectrophoretic field. Fusion between a cell vitally stained with Janus Green and that with Neutral Red resulted in the homokaryon with a mixed color. Intracellular potentials simultaneously recorded from the two cells located on both sides of the homokaryon were identical. The fusion efficiency was remarkably dependent upon temperature, displaying a discontinuity at about 11°C in the Arrhenius plot. The extracellular application of phospholipase-A2 or-C suppressed the fusion yield. Thus, it appears that the phospholipid domains play a crucial role in the electric pulse-induced cell fusion. Treatment of the cells with proteolytic enzymes markedly enhanced the fusion yield, presumably due to removing the glycocalix and/or giving rise to fusion-potent, protein-free lipid domains. The presence of millimolar concentrations of divalent cations (irrespective of Mg2+ or Ca2+) as well as of micromolar concentrations of Ca2+ (but not Mg2+) was prerequisite to the resealing of membranes suffered from electrical breakdown upon exposure to electric pulses. In addition, extracellular Ca2+ (but not Mg2+) ions at more than micromolar concentrations were indispensable for the cell fusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871522
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  • 17
    Electronic Resource
    Electronic Resource
    Tight junction formation in cultured epithelial cells (MDCK) (1985)
    Springer
    The journal of membrane biology 86 (1985), S. 113-125 
    Details
    ISSN: 1432-1424
    Keywords: epithelial monolayers ; MDCK cells ; tight junctions ; calcium ; biosynthesis of junctions ; junctional assembly ; apical/basolateral polarization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Synthesis and assembly of tight junctions are studied in monolayers of MDCK cells plated at a density sufficient for confluence, allowed to attach for 1 hr, and transferred to fresh media without cells containing or not Ca2+, 20 hr later, while monolayers with Ca2+ have fully developed junctions that confer an electrical resistance across of 346±51 Ω cm2, those without Ca2+ have a negligible resistance. If at this time Ca2+ is added, junctions assemble and seal with a fast kinetics, that can be followed through the development of electrical resistance, penetration of ruthenium red, and electron microscopy. Drugs that impair synthesis, maturation and transport of proteins (cycloheximide, tunicamycin, monensin) indicate that protein components are synthesized early upon plating, do not seem to require N-glycosylation, and are stored in the Golgi compartment. Upon addition of Ca2+ they are transferred to the membrane with the participation of microfilaments but not of microtubules. These components seem to insert directly in the position they occupy in the strands, and the cell circles its perimeter with one strand as early as 15 min, even if in some segments it only consists of a row of particles. New strands develop in association with previous ones, and the pattern completes in 4 to 6 hr. Ca2+ is required for the maintenance of the assembly and also for the sealing with neighboring cells. These processes cannot occur below 25°C. Serum is not required. Polarized distribution of intramembrane particles (IMP) in apical and basolateral regions follows the same time course as junction formation, in spite of the fence constituted by those strands that are already assembled. This suggests that IMP do not redistribute by lateral displacements in the plane of the membrane, but by removal and insertion in the apical and basolateral domains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870778
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  • 18
    Electronic Resource
    Electronic Resource
    The chromaffin granule proton pump and calcium-dependent exocytosis in bovine adrenal medullary cells (1985)
    Springer
    The journal of membrane biology 83 (1985), S. 147-156 
    Details
    ISSN: 1432-1424
    Keywords: Exocytosis ; proton pump ; calcium ; secretion ; adrenal medulla
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Calcium-dependent exocytosis in ‘leaky’ bovine adrenal medullary cells has a requirement for Mg-ATP. One possibility is that exocytosis depends in some way on the operation of the ATP-dependent proton pump that serves to maintain the core of the secretory vesicles both acid and at a positive potential with respect to the cytosol. This possibility has been tested in ‘leaky’ cells by monitoring exocytosis under conditions where the secretory vesicle pH and potential gradients are measuredin situ. The results show rather clearly that exocytosis can persist, with unchanged Ca-activation kinetics, in the virtual absence both of a difference in pH between the cytosol and secretory vesicle core and also of a difference in potential across the vesicle membrane. The results do not, however, exclude a small modulating effect of vesicle pH or potential on exocytosis and shed no light on whether or not the plasma membrane potential, which is maintained close to zero in these experiments, influences exocytosis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868746
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  • 19
    Electronic Resource
    Electronic Resource
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01869306
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  • 20
    Electronic Resource
    Electronic Resource
    Polycation inhibition of exocytosis from sea urchin egg cortex (1986)
    Springer
    The journal of membrane biology 91 (1986), S. 85-96 
    Details
    ISSN: 1432-1424
    Keywords: exocytosis ; polycations ; cortical lawn ; calcium ; sea urchin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The Ca2+-stimulated release of vesicle contents from cortical fragments prepared from sea urchin eggs is an in vitro model for exocytosis. Cortical fragments have been isolated either in suspension (cell surface complex, CSC preparation), or attached to polycation-coated surfaces (cortical lawn, CL preparation). CL, but not CSC, have been reported to undergo a rapid “aging” process whereby they fail to respond to micromolar free Ca2+. Since, in principle, the only difference between the two preparations is the use of polycations in the CL preparation, polycations were suspected of being inhibitory. This hypothesis was tested by evaluating the effects of polycation-containing buffers on the Ca2+ threshold, rate, and extent of exocytosis in CL prepared from the eggs ofStrongylocentrotus purpuratus. A sensitive microphotometric assay, based on light scattering by the individual cortical vesicles in the CL, was used to quantitate the exocytotic response. Buffers containing polylysine were found to be potent inhibitors of cortical exocytosis. The Ca2+ threshold of CL that had been treated for 15 min at room temperature with 50 μg/ml of polylysine was more than three orders of magnitude greater than that of freshly prepared CL. The other polycations tested (protamine, spermine and neomycin) were also found to be inhibitory, but to a lesser degree than polylysine. Two lines of evidence suggested that the polycations used in the preparation of CL are responsible for the rapid “aging” phenomenon: (i) CSC fragments that had been affixed to polylysine-coated coverslips were shown to aquire “aging” characteristics similar to the CL preparations; control CSC that had been maintained in suspension did not. (ii) Radiolabeled poly-l-lysine was shown to dissociate from coated coverslips and redistribute onto CL.
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    URL: http://dx.doi.org/10.1007/BF01870218
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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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    URL: http://dx.doi.org/10.1007/BF01871189
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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 
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    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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    URL: http://dx.doi.org/10.1007/BF01870621
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    Transcellular ion currents and extension ofNeurospora crassa hyphae (1988)
    Springer
    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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    URL: http://dx.doi.org/10.1007/BF01872817
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    Effect of phospholipid surface charge on the conductance and gating of a Ca2+-activated K+ channel in planar lipid bilayers (1985)
    Springer
    The journal of membrane biology 83 (1985), S. 273-282 
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    ISSN: 1432-1424
    Keywords: surface charge ; potassium channel ; calcium ; phosphatidylserine ; planar bilayer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary A Ca-activated, K-selective channel from plasma membrane of rat skeletal muscle was studied in artificial lipid bilayers formed from either phosphatidylethanolamine (PE) or phosphatidylserine (PS). In PE, the single-channel conductance exhibited a complex dependence on symmetrical K+ concentration that could not be described by simple Michaelis-Menten saturation. At low K+ concentrations the channel conductance was higher in PS membranes, but approached the same conductance observed in PE above 0.4m KCl. At the same Ca2+ concentration and voltage, the probability of channel opening was significantly greater in PS than PE. The differences in the conduction and gating, observed in the two lipids, can be explained by the negative surface charge of PS compared to the neutral PE membrane. Model calculations of the expected concentrations of K+ and Ca2+ at various distances from a PS membrane surface, using Gouy-Chapman-Stern theory, suggest that the K+-conduction and Ca2+-activation sites sense a similar fraction of the surface potential, equivalent to the local electrostatic potential at a distance of 9 Å from the surface.
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    URL: http://dx.doi.org/10.1007/BF01868701
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    Parathyroid hormone-induced changes of the brush border topography and cytoskeleton in cultured renal proximal tubular cells (1986)
    Springer
    The journal of membrane biology 92 (1986), S. 151-162 
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    ISSN: 1432-1424
    Keywords: kidney ; parathyroid hormone ; angiotensin II ; calcium ; brush border ; cytoskeleton
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In order to examine the possibility of parathyroid hormone-mediated ultrastructural rearrangements in target epithelium, isolated canine renal proximal tubular cells were grown on a collagen-coated semipermeable membrane in a defined medium. Scanning and transmission electron microscopy of these monolayers revealed abundant microvilli. Exposure of the proximal tubular cells to parathyroid hormone resulted in a biphasic changes involving: (1) dramatic shortening and rarefaction of microvilli within 1 min; and (2) recovery of microvillar topography after 5 min. A similar shortening of microvilli was observed following exposure to ionomycin, whereas incubation with cyclic AMP resulted in an elongation of microvilli. Parathyroid hormone stimulated cyclic AMP production and increased cytoplasmic free calcium concentration in cultured proximal tubular cells. Pretreatment of cells with a calmodulin inhibitor abolished the effect of parathyroid hormone on brush border topography. Shortening of microvilli was associated with a disappearance of microvillar core filaments. Staining of F-actin with fluoresceinphalloidin showed that parathyroid hormone resulted in fragmentation of stress fibers. It is concluded that parathyroid hormoneinduced cell activation involves cytoplasmic-free calcium, calmodulin, and the cytoskeleton.
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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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    Single Cl− channels in molluscan neurones: Multiplicity of the conductance states (1985)
    Springer
    The journal of membrane biology 86 (1985), S. 9-15 
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    ISSN: 1432-1424
    Keywords: molluscan neurone ; patch voltage-clamp technique ; single Cl channel ; calcium ; potassium ; multiplicity of the condutance states
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Properties of the single Cl− channels were studied in excised patches of surface membrane from molluscan neurones using single-channel recording technique. These channels are controlled by Ca2+ and K+ acting on cytoplasmic and outer membrane surfaces, respectively, and by the membrane potential. The channels display about 16 intermediate conductance sublevels, each of them being multiples of ∼12.5 pS. The upper level of the channel conductance is about 200 pS. The channel behavior is consistent with an aggregation of channel-forming subunits into a cluster.
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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 
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    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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    Heterogeneity of calcium compartmentation: Electron probe analysis of renal tubules (1986)
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    The journal of membrane biology 94 (1986), S. 191-196 
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    ISSN: 1432-1424
    Keywords: calcium ; kidney proximal tubule ; electron probe ; X-ray microanalysis ; mitochondria ; cytoplasmic calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The objective of this study has been to determine the intracellular localization of calcium in cryofixed, cryosectioned suspensions of kidney proximal tubules using quantitative electron probe X-ray microanalysis. Two populations of cells have been identified: 1) „Viable” cells, representing the majority of cells probed, are defined by their relatively normal K/Na concentration ratio of ∼4∶1. Their measured Ca content is 4.1±1.4 (sem) mmol/kg dry wt in the cytoplasm and 3.1 ± 1.1 mmol/kg dry wt in the mitochondria, or an average cell calcium content of ∼3.8 mmol/kg dry wt. 2) “Nonviable” cells, defined by the presence of dense inclusions in their mitochondria and a K/Na concentration ratio of ∼1. The Ca content is 15±2 mmol/kg dry wt in the cytoplasm and 685±139 mmol/kg dry wt in the mitochondria of such cells. Assuming 25 to 30% of the cell volume is mitochondrial, the overall calcium content of such nonviable cells is ∼ 210 mmol/kg dry wt. The presence of these inclusions in 4 to 5% of the cells would account for the average total Ca content measured in perchloric acid extracts of isolated proximal tubule suspensions (≈ 18 nmol/mg protein or 12.6 mmol/kg dry wt). Whole kidney tissues display a large variability in toal Ca content (4.5 to 18 nmol/mg protein, or 3.4 to 13.5 mmol/kg dry wt), which could be accounted for by inclusion in 0 to 4% of the cells. The electron probe X-ray microanalysis (EPXMA) data conclusively demonstrate that thein situ mitochondrial Ca content of viable cells from the kidney, proximal tubule is low and support the idea that mitochondrial Ca may regulate dehydrogenase activity but probably does not normally control cytosolic free Ca.
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    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 
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    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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    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 
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    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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    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 
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    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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    Effects of calcium on the gramicidin A single channel in phosphatidylserine membranes (1987)
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    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)
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    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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    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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    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
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    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00842411
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    Role of Ca++ in vasodilator reactions (1986)
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    Bulletin of experimental biology and medicine 101 (1986), S. 150-154 
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    ISSN: 1573-8221
    Keywords: α-adrenoreceptors ; metabolism ; calcium ; hormone-dependent vasodilatation
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    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00836103
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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 
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    ISSN: 1573-8221
    Keywords: c-src locus ; calcium ; Na+, K+-cotransport
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    Topics: Biology , Medicine
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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 
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    ISSN: 1573-8221
    Keywords: luteinizing hormone ; sex steroids ; calcium ; verapamil
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    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)
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    Bulletin of experimental biology and medicine 103 (1987), S. 518-520 
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    ISSN: 1573-8221
    Keywords: calcium ; spontaneous hypertension ; orthovanadate
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    URL: http://dx.doi.org/10.1007/BF00842486
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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
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    Mechanisms of platelet aggegation in experimental hypoparathyroidism (1986)
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    Bulletin of experimental biology and medicine 102 (1986), S. 1648-1650 
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    ISSN: 1573-8221
    Keywords: hypoparathyroidism ; platelet aggregation ; calcium ; arachidonic acid ; PAF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00840784
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    Antioxidant-induced calcium transport in biological membranes (1987)
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    Bulletin of experimental biology and medicine 104 (1987), S. 1220-1223 
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    ISSN: 1573-8221
    Keywords: biological membranes ; antioxidant ; calcium
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    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00841997
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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
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    URL: http://dx.doi.org/10.1007/BF00835687
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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
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    URL: http://dx.doi.org/10.1007/BF00802170
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    Cation-induced aggregation of membrane vesicles isolated from vascular smooth muscle (1986)
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    Journal of bioenergetics and biomembranes 18 (1986), S. 487-505 
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    ISSN: 1573-6881
    Keywords: Membrane aggregation ; smooth muscle plasma membranes ; calcium ; blood vessels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract Cations stimulated aortic muscle membrane aggregation with increasing potency according to their effective charge, e.g., K+〈Mg2+〈La3+, and the stimulation is reciprocally related to the apparent affinity for these cations. Divalent metal ion-induced membrane aggregation showed a dependence on the ionic radius, being optimal for Cd2+. Polyvalent cation-induced membrane aggregation was reversibly suppressed by high ionic strength as well as by metal ion chelators, irreversibly inhibited by the cross-linking agent glutaraldehyde, and enhanced by increasing concentrations of ethanol and increased temperature of the medium. When the pH is lowered below 6.0, membrane aggregation progressively increased with a concomitant decrease in cation-induced aggregation. The patterns of aggregation of microsomal membranes and further purified plasma membranes were almost identical whereas the aggregation of the heterogeneous mitochondrial membrane-enriched fraction was distinctly different in the initial rate of aggregation, its pH dependence, and metal ion concentration dependence. Our results indicate that cation-induced membrane aggregation can also be used to isolate a plasma membrane-enriched fraction from vascular smooth muscle.
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    Properties of potassium activatedp-nitrophenyl phosphatase of plasma membranes isolated from rat stomach muscle (1986)
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    Journal of bioenergetics and biomembranes 18 (1986), S. 295-306 
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    ISSN: 1573-6881
    Keywords: Smooth muscle ; sodium pump ; p-nitrophenyl phosphatase ; plasma membranes ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Physics
    Notes: Abstract The plasma membrane-enriched fraction isolated from smooth muscle of rat gastric fundus was found to contain a substantial level of potassium-stimulatedp-nitrophenylphosphatase activity (K-pNPPase), and its subcellular distribution closely resembled that of other plasma membrane enzyme markers. The kinetic profile of K-pNPPase and its sensitivity toward ouabain and vanadate confirmed the identification of this activity with the partial reaction of the sodium pump. The specific activity of K-pNPPase and its sensitivity to ouabain was significantly increased in the presence of saponin, indicating that part of this activity is latent when assayed on native membrane preparation. K-pNNPase was sensitive to the presence of calcium ions in the assay medium. The Ca2+-inhibition of K-pNNPase was accompanied by increased sensitivity of the enzyme to ouabain. On the other hand, calmodulin and Ca antagonists had no effect on K-pNPPase activity nor its sensitivity to calcium.
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    The mechanism of lead-induced mitochondrial Ca2+ efflux (1987)
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    Journal of bioenergetics and biomembranes 19 (1987), S. 285-295 
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    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.
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    Action of cyclosporine on mitochondrial calcium fluxes (1987)
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    Journal of bioenergetics and biomembranes 19 (1987), S. 297-303 
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    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.
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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 
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    ISSN: 1573-6881
    Keywords: Mitochondria ; diethylpyrocarbonate ; heart ; inhibition ; sodium ; calcium
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    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.
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    Control of mitochondrial Ca2+ retention by ADP-stimulated glutamic dehydrogenase (1987)
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    Journal of bioenergetics and biomembranes 19 (1987), S. 571-580 
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    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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    Mineral Metabolism of Aging Female Rats Fed Various Commercially Available Calcium Supplements or Yogurt (1988)
    Springer
    Pharmaceutical research 5 (1988), S. 501-505 
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    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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    Regulation of tetanus toxin-inhibited transmitter release in neuromuscular junctions in a calcium-free medium (1985)
    Springer
    Bulletin of experimental biology and medicine 99 (1985), S. 417-420 
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    ISSN: 1573-8221
    Keywords: rat neuromuscular junction ; calcium ; tetanus toxin ; ouabain
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
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    URL: http://dx.doi.org/10.1007/BF00842727
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    Combined inotropic effect of strophanthin and calcium on heart muscle (1985)
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    Bulletin of experimental biology and medicine 99 (1985), S. 317-320 
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    ISSN: 1573-8221
    Keywords: strophanthin G ; calcium ; contractile function of heart muscle
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    URL: http://dx.doi.org/10.1007/BF00799077
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    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 
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    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.
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    Calcitonin-like peptide in the shrimpPalaemon serratus (Crustacea, Decapoda) during the intermolt cycle (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 419-420 
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    ISSN: 1420-9071
    Keywords: Crustacean ; calcitonin ; radioimmunoassay ; calcium ; molt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary A molecule immunologically related to salmon calcitonin has been detected in the hemolymph of the shrimpPalaemon serratus. Its concentration varies inversely with the calcium level during the molt cycle; a maximum (14 ng/ml) is found in the post-molt stage and a minimum (0.5 ng/ml) during the premolt stage.
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    Release of calcitonin gene-related peptide from a human medullary carcinoma of the thyroid in vitro (1986)
    Springer
    Cellular and molecular life sciences 42 (1986), S. 829-830 
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    ISSN: 1420-9071
    Keywords: Calcitonin gene-related peptide ; calcitonin ; calcium ; perifusion ; medullary carcinoma of thyroid
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The secretion of human calcitonin gene-related peptide was examined in perifusates of medullary carcinoma of the thyroid with a sensitive radioreceptor assay. Calcitonin gene-related peptide was released after the addition of calcium (25–100 mM), in a dose-dependent manner. The results indicate that human medullary carcinomas of the thyroid secrete the calcitonin gene-related peptide as well as calcitonin.
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    Biological effects of lithium: Experimental analysis in plant cytokinesis (1987)
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    Cellular and molecular life sciences 43 (1987), S. 1025-1027 
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    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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    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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    Energetics and regulation of crossbridge states in mammalian smooth muscle (1985)
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    Cellular and molecular life sciences 41 (1985), S. 1020-1025 
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    ISSN: 1420-9071
    Keywords: Smooth muscle energetics ; light chain phosphorylation ; crossbridges ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Conclusion On the basis of measurements of the high energy phosphate usage associated with different mechanical states, as well as the degree of myosin light chain phosphorylation and mechanical properties, information has been gained concerning the existence and regulation of different crossbridge states in smooth muscle. Although incomplete, a general operational scheme is shown in figure 5. At very low intracellular calcium concentrations, actin and myosin are dissociated, as shown by a loss of resistance to stretch in resting muscles. At somewhat higher intracellular calcium concentrations in atonic, resting muscles, crossbridges can attach and be manifest mechanically as an increased resistance to stretch without ATP-driven crossbridge cycling and active force production. When the muscle is activated, intracellular calcium increases further, the light chains of myosin are phosphorylated through the calcium-calmodulin activation of myosin light chain kinase, actin-activated myosin ATPase activity increases and crossbridges cycle. Calcium also appears to modulate the ATPase activity and the rate of cycling of the phosphorylated crossbridge. The crossbridge cycling rate is highest during force development and slows with time as maximum isometric force is maintained reflecting a change in the rate at which phosphorylated crossbridges cycle. This may result from a decrease in the intracellular free calcium concentration with continued stimulation. During relaxation, the intracellular calcium concentration decreases, there is net dephosphorylation of the myosin light chains, the rate at which phosphorylated crossbridges cycle slows further with a gradual return to the attached, but non-cycling state or the detached state.
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    Morphological evidence for calcium storage in the chromatoid body of rat spermatids (1989)
    Springer
    Cellular and molecular life sciences 45 (1989), S. 377-378 
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    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.
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    Ionic currents in morphogenesis (1988)
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    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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    Arsenazo, 2-(4-arsonophenyl(azo-7-(4-antipyril)azo-1,8-dihydroxy-3,6-naphtalene disulphonic acid as reagent for calcium ions. New parameters for metallochromic indicator characterization (1986)
    Springer
    Microchimica acta 88 (1986), S. 73-85 
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    ISSN: 1436-5073
    Keywords: arsenazo ; calcium ; titration ; tristimulus-colorimetry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ca(II) ions react with arsenazo, 2-(4-arsonophenyl)-azo-7-(4-antipyril)azo-l,8-dihydroxy-3,5-naphtalene disulphonic acid, at pH 10.0 to produce a blue complex, with stoichiometry 1∶1, and stability constant of 6.64×105. Its molar absorptivity is 3.78×1041·mol−1 cm−1. This reagent has been used as metallochromic indicator in the complexometric titration of Ca. Its colour transition has been specified by tristimulus colourimetry. New parameters are defined and compared to Ringbom's parameters.
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    A fluorescence polarization procedure for the evaluation of the effects of cadmium and calcium on plasma membrane fluidity (1985)
    Springer
    Methods in cell science 9 (1985), S. 11-17 
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    ISSN: 1573-0603
    Keywords: fluorescence polarization ; membrane fluidity ; rat hepatocytes ; cadmium ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene (DPH) incorporated into plasma membranes of parenchymal hepatocytes provides a simple method of monitoring the immediate interactions of divalent cations with these membranes. Excitation of the fluorescent probe with vertically polarized light and monitoring of the vertical and horizontal components of the emitted light during the excited state lifetime of the probe provides a measure of DPH rotation. Membrane fluidity is evaluated on the basis of rotation of the fluorescent probe. Direct measurements of intermolecular events within plasma membranes are obtained after perturbation by individual metals and metalloids or combinations thereof. This technique has been useful in monitoring the effects of increasing concentrations of calcium or of increasing concentrations of cadmium in the presence or absence of calcium. Interactions of plasma membranes with such divalent metal cations, as well as other toxic substances, probably represents the first step in the series of cytotoxic reactions manifested by parenchymal hepatocytes.
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    Cultivation, frozen storage, and clonal growth of normal human epidermal keratinocytes in serum-free media (1985)
    Springer
    Methods in cell science 9 (1985), S. 83-93 
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    ISSN: 1573-0603
    Keywords: keratinocytes ; human ; epidermis ; serum-free ; calcium ; differentiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Methods are described for serum-free culture of human epidermal keratinocytes derived from neonatal foreskin tissue. Cultures are initiated, stored frozen, and returned to active growth, all with bovine pituitary extract as the only undefined supplement. Clonal growth assays are then performed in a biochemically defined medium. The degree of stratification and differentiation in the defined medium (and also with pituitary extract) is controlled by the extracellular calcium ion concentration.
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    The variation of element contents in triticale during vegetative growth (1987)
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    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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    URL: http://dx.doi.org/10.1007/BF01064828
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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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    Studies on the structure and physiology of salmon teleocalcin (1989)
    Springer
    Fish physiology and biochemistry 7 (1989), S. 367-374 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF00004730
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    Signals controlling renin release in aglomerular toadfish (1989)
    Springer
    Fish physiology and biochemistry 7 (1989), S. 323-329 
    Details
    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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    URL: http://dx.doi.org/10.1007/BF00004724
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    The enkephalin-containing cell: Strategies for polypeptide synthesis and secretion throughout the neuroendocrine system (1987)
    Springer
    Cellular and molecular neurobiology 7 (1987), S. 339-352 
    Details
    ISSN: 1573-6830
    Keywords: enkephalin ; neuropeptide ; secretion ; biosynthesis ; calcium ; cyclic AMP ; gene regulation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. Enkephalinergic cells are found throughout the diffuse neuroendocrine system, in the adrenal medulla, brain, spinal cord, peripheral and enteric nervous systems, and endocrine pancreas. 2. In each of these diverse cell types, the enkephalin phenotype is (i) established during development, (ii) modified by the particular environment in which the cell is located, and (iii) maintained by ongoing biosynthesis at a rate consistent with loss of enkephalins from the cell during periods of secretion. 3. Enkephalin expression and biosynthesis have been studied in several neuroendocrine cell types and tumor cell lines. Transcriptional, translational, and posttranslational factors can play a role at all three stages (establishment, modification, and maintenance) in the regulation of enkephalin expression during the lifetime of the cell. 4. Cyclic nucleotides, glucocorticoids, and calcium may all act to control the overall level of enkephalin biosynthesis pretranslationally, while regulation of posttranslational processing of proenkephalin seems to be important in determining the pattern of proenkephalin-derived opiate peptides produced in a given tissue. 5. The themes (and variations) of cell regulation that apply to enkephalin expression may be similar for other bioactive peptides produced in neural and endocrine tissues.
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    Dual regulation of ACTH secretion by guanine nucleotides in permeabilized AtT-20 cells (1988)
    Springer
    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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    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 
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    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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    A possible mechanism of morphometric changes in dendritic spines induced by stimulation (1985)
    Springer
    Cellular and molecular neurobiology 5 (1985), S. 47-63 
    Details
    ISSN: 1573-6830
    Keywords: dendritic spines ; synaptic plasticity ; spine apparatus ; calcium ; actin filaments ; spine apparatus as a calcium-sequestering organelle ; contractile proteins may underlie synaptic plasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. A number of experimental procedures which induce increased electrical activity (including long-term potentiation) were shown to be accompanied by morphometric changes in dendritic spines. These changes include an enlargement of the spine head, shortening and widening of the spine stalk, and an increase in the length of synaptic apposition. 2. A possible mechanism is suggested which takes into account specific cytological features of the spine and the existence of contractile proteins in neurons. Dendritic spines are defined as special domains of the neuron which have a unique organization of the cytoplasm. Actin filaments form a very dense network in the spine head, and they are longitudinally organized within the spine stalk. Spines were also shown to contain myosin and other actin-regulatory proteins. The high density of the actin network could explain the characteristic absence of the cytoplasmic organelles from dendritic spines. 3. In analogy with other cells, such an actin organization indicates low levels of free cytosolic calcium. Even in the resting state, calcium levels may be unevenly distributed through the neuron, being lowest within the subplasmalemmal region. Due to the high surface-to-volume ratio in spines, the cytoplasm is formed mostly by the subplasmalemmal region. The spine apparatus or the smooth endoplasmic reticulum, which is recognized as a calcium-sequestering site in spines, may also contribute to the low calcium levels there. 4. However, when in the stimulated spine the voltage-dependent calcium channels open, then, given the spine's high surface-to-volume ratio, the concentration of calcium may very quickly attain levels that will activate the actin-regulatory proteins and myosin and thus trigger the chain of events leading to the enlargement of the spine head and to the contraction (i.e., widening and shortening) of the spine stalk. The increased free cytosolic calcium may also activate the protein-producing system localized at the base of the spine, which, under certain conditions, could stabilize the morphometric changes of the spine.
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    URL: http://dx.doi.org/10.1007/BF00711085
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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.
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    URL: http://dx.doi.org/10.1007/BF00734991
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    Activity-dependent presynaptic facilitation: An associative mechanism inAplysia (1985)
    Springer
    Cellular and molecular neurobiology 5 (1985), S. 123-145 
    Details
    ISSN: 1573-6830
    Keywords: activity dependence ; adenylate cyclase ; associative learning ; calcium ; classical conditioning ; cyclic AMP ; presynaptic facilitation ; synaptic plasticity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. In studying the classical conditioning of the siphon withdrawal reflex inAplysia, we have identified a neuronal mechanism that plays an important role in this conditioning: activity-dependent presynaptic facilitation. This review describes our analysis of the cellular basis of this associative mechanism. During the conditioning of the withdrawal reflex, the unconditioned stimulus, a tail shock, produces presynaptic facilitation of synaptic transmission from the siphon sensory neurons in the conditioned stimulus pathway. The facilitation is enhanced if a sensory neuron has fired action potentials just prior to receiving facilitatory input, as occurs during training when the conditioned stimulus precedes the unconditioned stimulus. This activity-dependent enhancement of presynaptic facilitation provides a mechanism for the temporal specificity in conditioning of the reflex. 2. Activity-dependent facilitation appears to involve the same cyclic AMP (cAMP)-dependent cascade that underlies presynaptic facilitation in these neurons in the absence of paired spike activity. Our evidence suggests that it is the transient elevation of intracellular Ca2+ that is responsible for the enhancement of the facilitation response by paired spike activity. Moreover, our preliminary results indicate that Ca2+/calmodulin is able to potentiate the activation of adenylate cyclase inAplysia neurons by facilitatory transmitter. Thus, the dual activation of the calmodulin-dependent cyclase by Ca2+ and transmitter may give this enzyme an important associative role in learning. In the conclusion, the possible phylogenetic generality of this associative mechanism is discussed as well as its possible role in activity-dependent processes in neuronal development.
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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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    Axonal contribution to subthreshold currents inaplysia bursting pacemaker neurons (1986)
    Springer
    Cellular and molecular neurobiology 6 (1986), S. 239-253 
    Details
    ISSN: 1573-6830
    Keywords: molluscan neuron ; axon ; pacemaker ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary 1. The contribution of axonal activity to the ionic currents which generate bursting pacemaker activity was studied by using the two-electrode voltage-clamp technique inAplysia bursting neuron somata in conjunction with intraaxonal voltage recordings. 2. Depolarizing voltage-clamp pulses applied to bursting cell somata triggered axonal action potentials. The voltage-clamp current recording exhibited transient inward current “notches” corresponding to each of the axonal spikes. The addition of 50µM tetrodotoxin (TTX) to the bathing medium blocked the fast axonal spikes and current notches, revealing a slower axonal spike which was blocked by the replacement of external Ca2+ with Co2+. 3. The inward current evoked by applying a depolarizing voltage-clamp pulse in the soma is distorted by the occurrence of the axonal Ca2+ spike. Elimination of the axonal spike, by injecting hyperpolarizing current into the axon, changes both the time course and the magnitude of the inward current. 4. The axonal Ca2+ spikes are followed by a series of Ca2+-dependent afterpotentials: a rapid postspike hyperpolarization, a depolarizing afterpotential (DAP) and, finally, a long-lasting postburst hyperpolarization. The long-lasting hyperpolarization is not blocked by 50mM external tetraethyl ammonium, an effective blocker of Ca2+-activated K+ current [I K(Ca)], and does not appear to reverse atE K. Hence, the axonal long-lasting hyperpolarization may not be due toI K(Ca). 5. Somatic voltage-clamp pulses in bursting neurons are followed by a slow inward tail current, which is sometimes coincident with a DAP in the axon. In some cells, the amplitude of the slow inward tail current is greatly reduced if axonal spikes and DAPs are prevented by hyperpolarization of the axon, while, in other cells, elimination of axonal activity has little effect. Therefore, the slow inward tail current is not necessarily an artifact of poor voltage-clamp control over the axonal membrane potential but probably results from the activation of an ionic conductance mechanism located partly in the axon and partly in the soma.
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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 
    Details
    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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    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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    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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    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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    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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    Oviposition behaviour of Dacus tryoni: The effects of some sugars and salts (1985)
    Springer
    Entomologia experimentalis et applicata 39 (1985), S. 61-71 
    Details
    ISSN: 1570-7458
    Keywords: Dacus tryoni ; Tephritidae ; Diptera ; fruit flies ; oviposition ; egg laying ; behaviour ; taste receptors ; chemoreceptors ; stimulant ; deterrent ; fructose ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Résumé Des mouches fruitières gravides du Queensland (Dacus tryoni), confinées au laboratoire dans des chambres d'oviposition sont stimulées par la présence de β-D(-)fructose, à pondre significativement plus d'oeufs dans un substrat gélosé. Ce composé est un véritable stimulant d'oviposition, accroissant le nombre d'oeufs déposés par mouche, plutôt que simplement localisant l'oviposition dans les substrats le contenant. Le fructose est effectif seulement lorsqu'il est accessible aux récepteurs gustatifs tarsaux et labelliaux et, apparement, agit en stimulant de plus fréquentes insertions de l'ovipositeur dans le substrat; le contact du fructose avec uniquement l'ovipositeur inséré, n'accroît pas l'oviposition. Le seuil de concentration pour obtenir une stimulation par le fructose est de 4 mM; la résponse maximale se produit à 50 mM et au delà, auxquelles concentrations l'oviposition est augmentée d'un facteur 6 par rapport au témoin, qu'il y ait ou non possibilité de choix de substrat. Le sucrose (testé à 100 et 1 000 mM) et le D-glucose (testé à 100 et 500 mM) ne stimulent pas l'oviposition chez D. tryoni. Le fructose favorise fortement l'oviposition grâce aux trous existants dans une surface impénétrable, et dans les conditions naturelles, D. tryoni l'utilise probablement comme un marqueur pour localiser les ruptures dans la peau des fruits, où l'insertion est plus facile. La présence de chlorure de calcium molaire dans la gélose fructose inhibe fortement l'oviposition, même lorsqu'il est inaccessible aux récepteurs gustatifs tarsaux et labelliaux. Le chlorure de sodium molaire n'est pas inhibiteur. Les ions calciums déploient apparemment leur effet inhibiteur par l'intermédiaire de récepteurs gustatifs localisés sur l'ovipositeur.
    Notes: Abstract Gravid Queensland fruit flies (Dacus tryoni) are stimulated by the presence of β-D(-) fructose to lay significantly more eggs in an agar substrate. Fructose is only effective when accessible to the tarsal and/or labellar gustatory sensilla; it greatly increases oviposition through holes in an impenetrable membrane. Threshold for the fructose effect is 4 mM, maximal response being at 50 mM and above. Sucrose and glucose are not oviposition stimulants for D. tryoni. In the field situation D. tryoni probably uses fructose as a marker to locate breaks in the skin of ripe fruit, where insertion of the ovipositor is easier. The flies are deterred from ovipositing in fructose agar by the presence of molar calcium chloride, even when this is inaccessible to the tarsal and labellar gustatory sensilla. Molar sodium chloride is not inhibitory. Calcium ions apparently exert their inhibitory effect via gustatory sensilla located on the ovipositor.
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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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    The possible involvement of gibberellins and calcium in tipburn of Chinese cabbage: Study of intact plants and detached leaves (1986)
    Springer
    Plant growth regulation 4 (1986), S. 3-11 
    Details
    ISSN: 1573-5087
    Keywords: Chinese cabbage ; tipburn ; gibberellins ; calcium ; water stress ; misting
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Spraying Chinese cabbage seedlings [Brassica pekinensis (Lour.) Rupr.] with the growth retardant daminozide (succinic acid-2,2-dimethylhydrazide) reduced tipburn of the mature plants. As the concentration of daminozide increased, the reduction in tipburn damage was correlated with increased calcium content in young susceptible leaves. This effect was much more pronounced in plants that were misted once a day during the head formation period. Incubation of detached Chinese cabbage leaves for 48 h (in the dark) in solutions which contained either EDTA or EGTA caused characteristic lesions at the leaf tips. The extent of the damage was reduced by including CaCl2 in the solutions. Leaves which were incubated in a solution of EDTA+GA3 or EGTA+GA3 were severely affected, with the latter solution being the more harmful. GA3 alone did not enhance tipburn. CaCl2 greatly reduced the effect of a complex of chelating agents and GA3. Leaves derived from daminozide-treated plants which were incubated in EDTA+GA3 were less affected with tipburn lesions than leaves of control plants treated with the same solutions. When detached leaves were water-stressed for 24 h prior to incubation in these solutions, the severity of tipburn symptoms increased. The possible interactions between GA, calcium chelation and tipburn development are discussed.
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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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    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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    In situ ion exchange resin bags to estimate forest site quality (1989)
    Springer
    Plant and soil 119 (1989), S. 186-190 
    Details
    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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    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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    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 
    Details
    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 deicing chloride salts on ion accumulation in spruce (Picea abies (L.) sp.) (1989)
    Springer
    Plant and soil 113 (1989), S. 3-11 
    Details
    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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    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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    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 
    Details
    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 
    Details
    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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    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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    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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    Honeylocust (Gleditsia triacanthos L.) root response to aluminium and calcium (1989)
    Springer
    Plant and soil 119 (1989), S. 181-185 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02370283
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  • 99
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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 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02377070
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  • 100
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    Electronic Resource
    The effect of mineral elements on the maturity of peanut seed (1988)
    Springer
    Plant and soil 106 (1988), S. 263-268 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02371222
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