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  • calcium  (184)
  • Springer  (184)
  • PANGAEA
  • 2010-2014
  • 2000-2004  (37)
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  • 1
    ISSN: 1572-9605
    Schlagwort(e): LaBaCuO ; calcium ; superconductivity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Elektrotechnik, Elektronik, Nachrichtentechnik , Physik
    Notizen: Abstract It has been reported that, by adding equal amounts of CaO and CuO to non superconducting La3Ba3Cu6O z (La-336), a series of superconductors with nominal compositions La3Ca y Ba3Cu6+y O z were prepared with maximum Ton c ∼ 80K. Similar studies on addition of CaO and CuO in nonsuperconducting LaBaCu2O z (La-112) resulted into superconducting LaCaBaCu3O z (La-1113). To date no attempt has been made to synthesize La2CaBa2Cu5O z (La-2125) superconducting phase by addition of CaO and CuO to non superconducting La2Ba2Cu4O z (La-224) system. Also no reports are published to study the effect of replacing larger La3+-ions (1.01Å) by smaller rare earth ions viz Y3+(0.89Å), Er3+(0.91Å), Gd3+(0.91Å) on the structural and superconducting properties of (La2−x R x )Ba2(Ca y Cu4+y )O z (LRBCaC); 0.0 ≤ x ≤ 0.5; y=2x system. In this paper, we report the method of synthesis, structural and superconducting property characterization using X-ray diffraction, oxygen content measurements using iodometry, resistivity measurements using d.c. four probe technique and a.c. susceptibility measurements in the temperature range RT to 15K. Also a comparative study, on the evolution of superconducting phase with Ca-concentration for different rare earth substitutions for LRBCaC system in the context of hole doping mechanism, is carried out.
    Materialart: Digitale Medien
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  • 2
    ISSN: 1432-203X
    Schlagwort(e): Key words Rubber tree ; Agrobacterium tumefaciens ; calcium ; gene transfer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The influence of CaCl2 was investigated on Agrobacterium tumefaciens-mediated gene transfer in Hevea brasiliensis friable calli which are usually proliferated on maintenance medium (MM) containing 9 mM CaCl2.Five A. tumefaciens strains (C58pMP90, C58pGV2260, AGL1, LBA4404 and EHA 105) and two binary vectors (pGIN and pCAMBIA2301) were tested and the strain EHA105pC2301 was selected to conduct further experiments. The calli were precultured on MM containing a range of CaCl2 concentrations, then inoculated with Agrobacterium suspension. Transfer of friable calli from MM containing 9 mM CaCl2 to calcium-free medium significantly enhanced the transient β-glucuronidase activity. Interestingly, the use of calcium-free Agrobacterium resuspension medium to inoculate friable calli again dramatically increased the transformation efficiency. Induction of Agrobacterium's virulence with acetosyringone remained an important factor to stimulate transformation.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    Springer
    Journal of thermal analysis and calorimetry 60 (2000), S. 675-681 
    ISSN: 1572-8943
    Schlagwort(e): calcium ; diffusion ; metastable defect ; oxide ion ; perovskite ; sputtering ; thin film ; titanate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Metastable defects of oxygen in calcium titanate thin films with perovskite structure were studied. Thin films of calcium titanate were deposited by a magnetron sputtering method. The oxygen defects were evaluated, using the results of oxygen diffusion experiments. The thin film process had tendencies of creation of a large amount of oxygen point defects and the wide range of non equilibrium solid solution at room temperature. Thecrystal distortion was increasing with deviation from the stoichiometric composition. Although the metastable defects were decreasing due to the annealing, annealed samples had more oxygen defects in a few magnitude orders than single crystals.
    Materialart: Digitale Medien
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  • 4
    ISSN: 1573-4919
    Schlagwort(e): perfused rat liver ; norepinephrine ; fatty acids ; metabolism ; ketogenesis ; calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The effects of norepinephrine on ketogenesis in isolated hepatocytes have been reported as ranging from stimulation to inhibition. The present work was planned with the aim of clarifying these discrepancies. The experimental system was the once-through perfused liver from fasted and fed rats. Fatty acids with chain lengths varying from 8-18 were infused. The effects of norepinephrine depended on the metabolic state of the rat and on the nature of the fatty acid. Norepinephrine clearly inhibited ketogenesis from long-chain fatty acids (stearate 〉 palmitate 〉 oleate), but had little effect on ketogenesis from medium-chain fatty acids (octanoate and laureate). With palmitate the decrease in oxygen uptake was restricted to the substrate stimulated portion; with stearate, the decrease exceeded the substrate stimulated portion; with oleate, oxygen uptake was transiently inhibited. Withdrawal of Ca2+ attenuated the inhibitory effects. 14CO2 production from [1-14C]oleate was inhibited. Net uptake of the fatty acids was not affected by norepinephrine. In livers from fed rats, oxygen uptake and ketogenesis from stearate were only transiently inhibited. The conclusions are: (a) in the fasted state norepinephrine reduces ketogenesis and respiration by means of a Ca2+-dependent mechanism; (b) the degree of inhibition varies with the chain length and the degree of saturation of the fatty acids; (c) norepinephrine favours esterification of the activated long-chain fatty acids in detriment to oxidation; (d) in the fed state the stimulatory action of norepinephrine on glycogen catabolism induces conditions which are able to reverse inhibition of ketogenesis and oxygen uptake.
    Materialart: Digitale Medien
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  • 5
    ISSN: 1573-4919
    Schlagwort(e): Na/K-ATPase ; calcium ; signal transduction ; ouabain ; Ras ; mitogen-activated protein kinase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Partial inhibition of Na/K-ATPase by ouabain causes hypertrophic growth and regulates several early and late response genes, including that of Na/K-ATPase α3 subunit, in cultured neonatal rat cardiac myocytes. The aim of this work was to determine whether ouabain and other hypertrophic stimuli affect Na/K-ATPase β1 subunit gene expression. When myocytes were exposed to non-toxic concentrations of ouabain, ouabain increased β1 subunit mRNA in a dose- and time-dependent manner. Like the α3 gene, β1 mRNA was also regulated by several other well-known hypertrophic stimuli including phenylephrine, a phorbol ester, endothelin-1, and insulin-like growth factor, suggesting involvement of growth signals in regulation of β1 expression. Ouabain failed to increase β1 subunit mRNA in the presence of actinomycin D. Using a luciferase reporter gene that is directed by the 5′-flanking region of the β1 subunit gene, transient transfection assay showed that ouabain augmented the expression of luciferase. These data support the proposition that ouabain regulates the β1 subunit through a transcriptional mechanism. The effect of ouabain on β1 subunit induction, like that on α3 repression, was dependent on extracellular Ca2+ and on calmodulin. Inhibitions of PKC, Ras, and MEK, however, had different quantitive effects on ouabain-induced regulations of β1 and α3 subunits. The findings show that partial inhibition of Na/K-ATPase activates multiple signaling pathways that regulate growth-related genes, including those of two subunit isoforms of Na/K-ATPase, in a gene-specific manner.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 209 (2000), S. 69-77 
    ISSN: 1573-4919
    Schlagwort(e): protein kinase C ; phorbol-binding domain ; protein interaction ; calcium ; phospholipids
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Protein kinase C-γ (PKC-γ) contains two cysteine-rich regions (Cys1, Cys2) responsible for interaction with phospholipids. However, previous experiments suggested that, only Cys1 represents the high affinity site involved in diacylglycerol-dependent activation of PKC-γ. This raises the question whether Cys2 might participate in other functions of the PKC-γ regulatory domain. The purpose of our studies was to examine the ability of Cys2 domain to bind cellular proteins. The Cys2 domain (residues 92-173) was expressed as a fusion protein with glutathione-S-transferase (GST) in Escherichia coli and purified. In order to investigate protein-protein interaction of Cys2 domain we used affinity column and an overlay assay. Our results demonstrate that the Cys2 domain of PKC-γ binds several proteins from rat brain extracts. In the absence of phospholipids the Cys2 domain binds some proteins in the cytosolic fraction of rat brain, but no binding was detected with the proteins extracted from particulate fraction. Ca2+ at 1 μM concentration potentiated binding of cellular proteins to Cys2 domain. In the absence of Ca2+ the Cys2 domain binds proteins in the cytosolic fraction of rat brain in the presence of phosphatidylserine and to the lesser extend in the presence of phosphatidylinositol but neither phosphatidylcholine nor phosphatidylethanolamine. These results suggest that the Cys2 domain of PKC-γ has the ability to interact with two classes of proteins. One class binds the Cys2 domain in the phosphatidylserine dependent fashion, and the other proteins bind Cys-2 domain in the Ca2+ dependent and phospholipid independent manner.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 203 (2000), S. 169-175 
    ISSN: 1573-4919
    Schlagwort(e): calcium ; heart ; rats ; fluorescence spectroscopy ; Indo-1
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Reperfusion of isolated mammalian hearts with a Ca2+-containing solution after a short Ca2+-free period at 37°:C results in massive influx of Ca2+ into the cells and irreversible cell damage: the Ca2+paradox. Information about the free intracellular, cytosolic [Ca2+] ([Ca2+]i) during Ca2+ depletion is essential to assess the possibility of Ca2+ influx through reversed Na+/Ca2+ exchange upon Ca2+ repletion. Furthermore, the increase in end-diastolic pressure often seen during Ca2+-free perfusion of intact hearts may be similar to that seen during ischemia and caused by liberation of Ca2+ from intracellular stores. Therefore, in this study, we measured [Ca2+]i during Ca2+- free perfusion of isolated rat hearts. To this end, the fluorescent indicator Indo-1 was loaded into isolated Langendorff-perfused hearts and Ca2+-transients were recorded. Ca2+-transients disappeared within 1 min of Ca2+ depletion. Systolic [Ca2+]i during control perfusion was 268±54 nM. Diastolic [Ca2+]i during control perfusion was 114±34 nM and decreased to 53±19 nM after 10 min of Ca2+ depletion. Left ventricular end-diastolic pressure (LVEDP) significantly increased from 13±4 mmHg during control perfusion after Indo-1 AM loading to 31±5 mmHg after 10 min Ca2+ depletion. Left ventricular developed pressure did not recover during Ca2+ repletion, indicating a full Ca2+ paradox. These results show that LVEDP increased during Ca2+ depletion despite a decrease in [Ca2+]i, and is therefore not comparable to the contracture seen during ischemia. Furthermore, calculation of the driving force for the Na+/Ca2+ exchanger showed that reversed Na+/Ca2+ exchange during Ca2+ repletion is not able to increase [Ca2+]i to cytotoxic levels.
    Materialart: Digitale Medien
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  • 8
    ISSN: 1573-4919
    Schlagwort(e): protein kinase C ; ζ-PKC ; pseudosubstrate ; calcium ; neutrophil
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Role of protein kinase C (PKC) isotypes in the regulation of neutrophil function are not clearly known. In the present study we purified the β-PKC and ζ-PKC isotypes from human neutrophil. Both the isotypes are immunoreactive only to their respective antibodies. ζ-PKC was further confirmed by RT-PCR using specific primer. Co-factor requirements for both the kinases were found to be different when DG and ceramide were used as second messenger. Selective substrate specificities were determined for both β and ζ-PKC using isotype specific pseudosubstrates viz., [Ser25]PKC [19-31] and [Ser119]PKC[113-130] respectively. Endogenous protein phosphorylation by purified β-PKC and ζ-PKC showed their functional differences in neutrophil. β-PKC phosphorylated 13, 15, 19, 33, 36, 47, 80 and 92 kDa proteins and ζ-PKC phosphorylated 19, 22, 42, 47, 75 and 87 kDa proteins, only exception was the phosphorylation of 47 kDa protein which had been phosphorylated by both the kinases. Differences in phosphorylation between β-PKC and ζ-PKC clearly indicate the selective role for these PKC isotypes in the activation sequences of neutrophil.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 209 (2000), S. 105-112 
    ISSN: 1573-4919
    Schlagwort(e): Ca2+-ATPase ; thermal analysis ; cholesterol ; calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The plasma membrane Ca2+-ATPase is a well known enzyme in eucaryotes able to extrude calcium to the extracellular space in order to restore intracellular calcium to very low levels. This ATPase needs plasma membrane lipids such as acidic phospholipids in order to maintain its activity. In this study, we investigated the role that calcium and cholesterol play on the thermal stability of the Ca2+-ATPase isolated from cardiac sarcolemma and erythrocyte membranes. Calcium showed a stabilizing and protective effect when the enzyme was exposed to high temperatures. This stabilizing effect showed by calcium was potentiated in the presence of cholesterol. These protection effects were reflected on several thermodynamic parameters such as T50, ▵Hvh and apparent ▵G, indicating that calcium might induce a conformational change stabilized in the presence of cholesterol that confers enzyme thermostability. The effect shown by cholesterol on ▵Hvh and apparent ▵H
    Materialart: Digitale Medien
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  • 10
    ISSN: 1573-4919
    Schlagwort(e): tumour necrosis factor ; receptors ; subtypes ; calcium ; apoptosis ; cancer
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Tumour necrosis factor-α (TNF) receptors mediate a variety of effects dependent on cell type. A role for Ca2+ in TNF-induced death remains uncertain. Here we investigated restricting intracellular/extracellular Ca2+ in HeLa epithelial carcinoma cells expressing low and high levels of p75TNFR receptor subtype and KYM-1 rhabdomyosarcoma cells, models of rapid TNF-induced apoptosis. Ca2+-chelators EGTA and BAPTA-AM as well as microsomal Ca2+-ATPase inhibitor thapsigargin, did not alter TNF-induced death. TNF was also unable to alter resting [Ca2+]i levels which remained 〈 200 nM even during times when these cells were undergoing apoptotic cell death. These findings indicate no role for modulated Ca2+ concentrations in TNF-induced apoptotic cell death.
    Materialart: Digitale Medien
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  • 11
    Digitale Medien
    Digitale Medien
    Springer
    Journal of chemical ecology 26 (2000), S. 2825-2841 
    ISSN: 1573-1561
    Schlagwort(e): Bats ; calcium ; folivory ; frugivory ; nutrition ; protein ; Pteropodidae
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract We evaluated organic and macromineral composition of selected fruits and leaves consumed by the short-nosed fruit bat, Cynopterus sphinx in South India. Results of principal components analysis (PCA) comparing soluble carbohydrates, crude protein, and crude fats indicate a higher percentage of protein in leaves and a higher percentage of carbohydrates and lipids in fruits. However, results of a paired t test comparing these organic components indicated no differences between fruits and leaves. Among the fruits analyzed, Musa x paradisiaca had the highest percentage of carbohydrates, and Psidium guajava had the highest percentage of lipids. Leaves of Cassia fistula, Moringa oleifera, coccinia cordifolia, and F. religiosa had the highest percentage of protein. PCA of selected macrominerals (Ca, Na, K, and P) indicate higher levels of Ca in leaves than in fruits. Results of t tests comparing these macrominerals revealed a difference between fruits and leaves for Ca, but not for the other macrominerals. Among the leaves analyzed, Ca was highest in mature leaves of C. fistula and lowest in leaves of F. religiosa. Leaves of M. oleifera and fruits of Achras sapota were highest in sodium. Among fruits analyzed for macrominerals, Ca was highest in F. bengalensis and lowest in Prosopis juliflora, A. sapota, and M. x paradisiaca. Potassium levels were highest in leaves of C. cordifolia and fruit pods of Prosopis juliflora. Phosphorus content was highest in leaves of M. oleifera and fruits of M. x paradisiaca. The relatively high concentrations of protein and calcium in leaves eaten by C. sphinx supports the hypothesis that leaves are important dietary sources for this plant-visiting bat.
    Materialart: Digitale Medien
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  • 12
    ISSN: 1573-4919
    Schlagwort(e): calcium ; pancreatic acinar cell ; dephostatin ; cholecystokinin ; amylase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract This study investigates the effects of dephostatin, a new tyrosine phosphatase inhibitor, on intracellular free calcium concentration ([Ca2+]i) and amylase secretion in collagenase dispersed rat pancreatic acinar cells. Dephostatin evoked a sustained elevation in [Ca2+]i by mobilizing calcium from intracellular calcium stores in either the absence of extracellular calcium or the presence of lanthanium chloride (LaCl3). Pretreatment of acinar cells with dephostatin prevented cholecystokinin-octapeptide (CCK-8)-induced signal of [Ca2+]i and inhibited the oscillatory pattern initiated by aluminium fluoride (AlF- 4), whereas co-incubation with CCK-8 enhances the plateau phase of calcium response to CCK-8 without modifying the transient calcium spike. The effects of dephostatin on calcium mobilization were reversed by the presence of the sulfhydryl reducing agent, dithiothreitol. Stimulation of acinar cells with thapsigargin in the absence of extracellular Ca2+ resulted in a transient rise in [Ca2+]i . Application of dephostatin in the continuous presence of thapsigargin caused a small but sustained elevation in [Ca2+]i . These results suggest that dephostatin can mobilize Ca2+ from both a thapsigargin-sensitive and thapsigargin-insensitive intracellular stores in pancreatic acinar cells. In addition, dephostatin can stimulate the release of amylase from pancreatic acinar cells and moreover, reduce the secretory response to CCK-8. The results indicate that dephostatin can release calcium from intracellular calcium pools and consequently induces amylase secretion in pancreatic acinar cells. These effects are likely due to the oxidizing effects of this compound.
    Materialart: Digitale Medien
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  • 13
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 206 (2000), S. 1-6 
    ISSN: 1573-4919
    Schlagwort(e): regucalcin ; calcium ; protease ; rat kidney cytosol ; saline ingestion ; hypertensive state
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The effect of regucalcin (RC) on neutral proteolytic activity in the cytosol of rat kidney cortex was investigated. Proteolytic activity was significantly increased by the presence of RC (0.01 + 0.10 μM) in the enzyme reaction mixture. This increase was completely abolished by the addition of anti-RC monoclonal antibody (150 ng/ml). When the renal cortex cytosol was incubated without RC addition, the degradation of globin of substrate was demonstrated by sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. This degradation was clearly inhibited by the addition of anti-RC antibody (150 ng/ml), indicating that protein degradation results partly from the cytosolic endogenous RC. Meanwhile, proteolytic activity was significantly decreased in the renal cortex cytosol of rats with saline ingestion for 2, 7, and 14 days. The effect of RC (0.1 μM) in increasing proteolytic activity was weakened in the kidney cortex cytosol of saline-ingested rats. The present study suggests that endogenous RC plays a role in the activation of proteases in the renal cortex cytosol, and that the RC effect is impaired in saline-ingested rats.
    Materialart: Digitale Medien
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  • 14
    ISSN: 1573-4919
    Schlagwort(e): human endothelial cells ; mechanical stress ; immediate early genes ; protein kinase C ; calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Restenosis after initially successful balloon angioplasty of coronary artery stenosis remains a major problem in clinical cardiology. Previous studies have identified pathogenetic factors which trigger cell proliferation and vascular remodeling ultimately leading to restenosis. Since there is evidence that endothelial cells adjacent to the angioplasty wound area synthesize factors which may initiate this process, we investigated the effects of mechanical stimulation on endothelial gene expression in vitro and focussed on the influence of sustained mechanical stress on expression of immediate early genes which have previously been shown to be induced in the vascular wall in vivo. Primary cultured human umbilical vein endothelial cells (HUVEC) and the human endothelial cell line EA.hy 926 were plated on collagen-coated silicone membranes and subjected to constant longitudinal stress of approximately 20% for 10 min to 6 h. Total RNA was isolated and the expression of the immediate early genes c-Fos and Egr-1 was studied by Northern blot analysis. We found a rapid upregulation c-Fos and Egr-1 mRNA which started at 10 min and reached its maxima at 30 min. HUVEC lost most of their stretch response after the third passage whereas immediate early gene expression was constantly in EA.hy 926 cells. Using specific inhibitors we investigated the contribution of several signal transduction pathways to stretch-activated Egr-1 mRNA expression. We found significant suppression of stretch-induced Egr-1 mRNA expression by protein kinase C (PKC) inhibition (p 〈 0.05) and by calcium depletion (EA.hy926, p 〈 0. 05; HUVEC, p = 0.063). No effect on stretch-activated Egr-1 mRNA expression was detected by inhibition of protein kinase A, blockade of stretch-activated cation channels or inhibition of microtubule synthesis. We conclude that sustained mechanical strain induces Egr-1 mRNA expression by PKC- and calcium-dependent mechanisms.
    Materialart: Digitale Medien
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  • 15
    Digitale Medien
    Digitale Medien
    Springer
    Bioscience reports 20 (2000), S. 93-98 
    ISSN: 1573-4935
    Schlagwort(e): ATPase ; calcium ; liver ; protein malnutrition ; transport ; tumor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract The effect of protein undernutrition on the activity of the smoothendoplasmic reticulum (microsomal) Ca2+-ATPase (SERCA) wasinvestigated. After 12 weeks of ad libitum ingestion of low proteindiet (5% protein), a significant depression (p〈0.05) of liver ERCa2+-ATPase activity (68.6% depression) was observed. However,no significant effects on cytochrome P450 activity and relative liverweight were found. It is proposed that low protein diet by inhibitingthe rat liver SERCA activity, might increase the cytosolic free calciumion concentration ([Ca2+]) and promote the development of livertumor. The possible mechanisms of low protein diet induced inhibition ofSERCA activity are highlighted.
    Materialart: Digitale Medien
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  • 16
    ISSN: 1573-5001
    Schlagwort(e): calcium ; cell adhesion ; NMR assignments
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Materialart: Digitale Medien
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  • 17
    Digitale Medien
    Digitale Medien
    Springer
    Neuroscience and behavioral physiology 30 (2000), S. 357-363 
    ISSN: 1573-899X
    Schlagwort(e): Anoxia ; brain slices ; calcium ; phosphoinositides ; adaptation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The involvement of the calcium and phosphoinositide intracellular regulatory systems in the molecular-cellular mechanisms of adaptation of the brain to hypoxia induced by transient anoxia were studied in slices of rat olfactory cortex. Anoxia lasting 2 min initiated the development of moderate but stable activation of intracellular regulatory systems during the reoxygenation period, with increases in binding of Ca2+ to intracellular hydrophobic domains and increases in the level of polyphosphoiositide metabolism. During this period, cells in the slices released neuromediator factors into the perfusion fluid; transfer of these to recipient slices induced similar changes in the activities of intracellular regulatory system components in the recipient slices. After anoxia lasting 10 min, NMDA-mediated pathogenic hyperactivity of the calcium and phosphoinositide systems developed. Preliminary moderate activation of these systems by transient anoxia or neuromodulator factors released by cells in response to transient anoxia prevented disruption of intracellular regulatory system activity induced by subsequent longer-lasting anoxia.
    Materialart: Digitale Medien
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  • 18
    Digitale Medien
    Digitale Medien
    Springer
    International journal of primatology 21 (2000), S. 69-83 
    ISSN: 1573-8604
    Schlagwort(e): tamarin ; saguinus ; exudate ; mineral ; calcium ; feeding
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract I provide the first comprehensive data on the composition and mineral content of exudates eaten by saddleback (Saguinus fuscicollis) and mustached tamarins (S. mystax) and assess Garber's (1984; 1993) hypotheses on the potential nutritional importance of exudates in the diet of tamarins. In accordance with his initial findings, nutritional analyses show that the gums consumed are relatively high in calcium and may serve to balance a diet otherwise low in this mineral and high in phosphorus. However, the data on the seasonal variation in the amount consumed do not support the hypothesis that exudates are of particular nutritional importance during the later stages of gestation or lactation for saddleback or mustached tamarins.
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  • 19
    ISSN: 1573-904X
    Schlagwort(e): transfection ; serum inhibition ; H1 histone ; DOSPER ; calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Purpose. One of the drawbacks of polycationic and cationic liposomalgene transfer is its sensitivity to serum. Gene therapy requires thetransfectant-DNA complex to be resistant to serum as well as blood.Since Ca2+ has proved to be an efficient cofactor of polycationic genetransfer, we decided to investigate its effects on transfection in thepresence of serum. Methods. We studied transgene expression of luciferase gene (pCMVLuc) on ECV 304 human endothelial cells using H1 histone andDOSPER as transfectants in the presence of 0-100% fetal calf serum. Results. H1-and DOSPER-mediated transfection was found to beinhibited by serum above the concentration of 10%. If 2 mM Ca2+ or2 mM Ca2+/0.1 mM chloroquine was included in the culture mediumwhich replace the transfection mixture and was left on the cells for24 hours postincubation, the inhibiting effect of even 100% serumwas overcome. Conclusions. A high serum level does not interfere with binding anduptake of H1- and DOSPER-DNA complexes, but inhibits subsequentsteps such as endosomal escape. Ca2+ in the form of nascent calciumphosphate microprecipitates and other lysosomolytical agents facilitateendosomal/lysosomal release by their fusigenic and membranolyticactivity.
    Materialart: Digitale Medien
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  • 20
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 218 (2000), S. 197-205 
    ISSN: 1573-5036
    Schlagwort(e): acid soil ; calcium ; cluster roots ; heterogeneous soil profile ; limed soil ; lupins
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The ability of Lupinus albus L. to adapt to a heterogeneous soil profile containing acid subsoil below limed topsoil of the same type, and to utilize nutrients by significantly altering its root system structure, was investigated using specially constructed soil profile tubes. Plants grown in homogeneous acid profiles had the fastest growth while those grown in homogeneous limed-soil profiles showed the slowest growth and exhibited some chlorosis after 19 days. Limed topsoil combined with an acid subsoil profile initially retarded plant growth similar to that in a homogeneous limed soil. However, after 68 days significantly greater growth had occurred in the limed/acid soil treatment relative to the homogeneous limed soil, indicating plants had benefited from the acid subsoil stratum. Plants in the homogeneous limed soil profile had lower concentrations of P, Fe and Mn in shoots compared with those in heterogeneous soils. In contrast, the concentration of Ca increased by 74%, due mainly to an increase in the water-soluble Ca fraction. When grown in a heterogeneous limed/acid soil profile, concentrations of P, Ca, K, Mg, Fe, Mn and Zn in shoots were comparable to those grown in a soil with a homogeneous acid profile. Although total root production was lower in the homogeneous limed-soil profile compared to the acid-soil containing profiles, cluster root mass was maintained at a level comparable with that in acid soil. The roots in heterogeneous soil profiles exhibited extensive plasticity, demonstrating a root-type specific, morphological response to the soil conditions. Within the acid subsoil of a heterogeneous profile, there was a large increase in cluster root mass compared with non-cluster roots. The proliferation of cluster roots in acid soil below limed topsoil may enhance the plant's ability to exploit this soil and facilitate the cultivation of L. albus on limed soil.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 21
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 225 (2000), S. 299-310 
    ISSN: 1573-5036
    Schlagwort(e): Acer pseudoplatanus L. ; calcium ; Fagus sylvatica L. ; Karst ; Picea abies L. ; strontium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract In favourable conditions, the 87Sr/86Sr isotope ratios of the Sr delivered by rain and soil mineral weathering differ. Assuming that Ca and Sr behave similarly in forest ecosystems, several authors have used the 87Sr/86Sr variation in forest compartments to calculate the contribution of rain and mineral weathering to Ca fluxes and pools. However, there are a number of experimental reports showing that Ca and Sr may behave differently in the soil and in the plant. We have tested this Ca–Sr analogy in the field by measuring the variation of Sr and Ca concentrations, fluxes and pools in spruce, beech and maple stands on granite, sandstone and limestone. Results show that (1) variations of Ca and Sr concentrations are generally correlated at each level of the ecosystems. (2) In spruce on acid soils, a preferential uptake of Ca over Sr occurs (Aubure spruce Sr/Ca = 0.8×10−3; soil exchangeable Sr/Ca between 2 and 6×10−3). On calcareous soils, a preferential uptake of Sr over Ca by spruce may occur. (3) In spruce and beech on acid and calcareous soils, a preferential translocation of Ca over Sr from roots to leaves occurs ((Sr/Ca) in leaves was between 10 and 90% of that in roots). (4) The biological cycling of Ca and Sr leads to an enrichment of the upper soil layers in Ca and Sr. Compared to Sr, Ca accumulates in the upper layer of acid soils because Ca cycling through litterfall is favoured over Sr cycling, and possibly because of the selectivity of acid organic exchangers for Ca.
    Materialart: Digitale Medien
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  • 22
    ISSN: 1573-5036
    Schlagwort(e): acid soil ; ammonium ; calcium ; magnesium ; nitrate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The effects of solution acidity and form of nitrogen on net nutrient uptake rates in Acer pseudoplatanus and Calamagrostis villosa seedlings were examined as part of a complex ecological study. Uptake rates were measured by the depletion method under controlled conditions (temperature 20 °C, irradiance 400 μmol m−2 s−1 PAR) from a nutrient solution containing 1.5 mM nitrogen in the form of nitrate or ammonium or an equimolar mixture of both. The solution acidity was kept constant at pH 5.5 (control treatment), 4.5 or 3.5 (low pH treatments). Strongly acid pH decreased or stopped the uptake rates of NO3 −, Mg2+ and Ca2+, but the uptake of NH4 + was not changed in both species. Ammonium ions reduced the uptake rate of NO3 − in Acer but increased the uptake rate in Calamagrostis. Ammonium as the sole source of nitrogen had a strong negative impact on the uptake rates of calcium and magnesium and this effect was independent of the media acidification usually connected with NH4 + uptake and assimilation. However, the negative effect of ammonium ions on the base cation uptake was more pronounced at low pH values.
    Materialart: Digitale Medien
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  • 23
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 220 (2000), S. 229-233 
    ISSN: 1573-5036
    Schlagwort(e): Acacia ; calcium ; potassium ; salinity tolerance ; seed germination
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Seeds of A. bivenosa DC. Prod., A. coriacea DC., A. elata A. Cunn. Ex Benth., A. farnesiana (L.) Willd., A. nilotica Willd. ex Del., A. salicina Lindl., A. saligna (Labill.) H. Wendle., A. senegal (L.) Willd., A. tortilis (Forsk.) Hayne and A. tumida F. Muell. ex Benth. were tested for their final germination percentage (FG) in distilled water (DW) and in 25–400 mol m-3 NaCl, germination rate (1/t50, where t50 is the time to 50% of final germination in DW), Ca and K concentration (Caunt, Kunt), the leakage of these ions when soaked for 24 h in DW (CaDW, KDW) and the leakage (additional to that in DW) when soaked in 250 mol m-3 NaCl (CaNaCl, KNaCl). Linear regression revealed significant positive relationships between salinity tolerance (I50, the concentration of NaCl required to reduce final germination to 50% of the control value in DW) and FG, Rate, Caunt/Kunt and CaNaCl/KNaCl. There was also a significant negative relationship between I50 and Kunt. Multiple regression equations were developed to predict I50 from the above parameters. Equations based on (1) FG and Rate, (2) Caunt and Kunt, and (3) any of these four factors, accounted for 61, 60 and 79%, respectively, of the variation in I50. Further equations, introducing the leakage of ions into DW and NaCl and the ratios of ion concentrations monitored, improved the predictive value of the equation. The best equation, accounting for 93% of the variation was: I50 = 108 + 422 Rate − 1.32 Kunt + 16.3 CaDW − 5.4 KDW + 71.6 K/CaDW. These equations provide a screening test for salt tolerance of Acaciaseed germination based on simple and rapid laboratory chemical analyses and germination tests.
    Materialart: Digitale Medien
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  • 24
    Digitale Medien
    Digitale Medien
    Springer
    Plant growth regulation 30 (2000), S. 49-54 
    ISSN: 1573-5087
    Schlagwort(e): calcium ; DNA degradation ; meristematic root cells ; salt stress ; soybean
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Changes in the nuclei of meristematic root cells of soybean (Glycine max (L.) Merr. cv. Acme) in response to severe salinity were studied. Root growth was inhibited by 200 mM NaCl, when 1 mM CaCl_2 was present in the culture media. Increasing CaCl_2 up to 5 mM partially prevented this inhibition. However, inhibition also occurred with 100~mM NaCl without CaCl_2. We examined the meristematic cells under a series of NaCl treatments. Nuclear deformation of the cells occurred with 24 h of 150 mM or higher NaCl, and was followed by degradation of nuclei in the apical region of the root. TEM observation and agarose gel electrophoretic analysis confirmed that root tip nuclear DNA deformed or degraded with 150 mM or higher NaCl concentrations.
    Materialart: Digitale Medien
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  • 25
    ISSN: 1573-515X
    Schlagwort(e): barium ; calcium ; food chain ; forest ; songbird ; strontium isotope
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Geologie und Paläontologie
    Notizen: Abstract The variability and biologicalfractionation of Sr/Ca, Ba/Ca and 87Sr/86Srratios were studied in a soil–plant–invertebrate–bird food chain in two forested ecosystems withcontrasting calcium availability in the northeasternU.S.A. Chemical measurements were made of the soilexchange pool, leaves, caterpillars, snails, and boththe femurs and eggshells of breeding insectivorousmigratory songbirds. 87Sr/86Sr values weretransferred up the food chain from the soil exchangepool to leaves, caterpillars, snails and eggshellswithout modification. Adult birds were the oneexception; their 87Sr/86Sr values generallyreflected those of lower trophic levels at each site,but were lower and more variable, probably becausetheir strontium was derived in part from foods intropical winter habitats where lower87Sr/86Sr ratios are likely to predominate. Sr/Ca and Ba/Ca ratios decreased at each successive trophiclevel, supporting previous suggestions that Sr/Ca andBa/Ca ratios can be used to identify the trophic levelat which an organism is primarily feeding. The changesin Sr/Ca and Ba/Ca ratios we measured for vegetationand insects were comparable to similar measurementsmade previously (but based on single samples of eachorganism) in an alpine ecosystem. Changes in Sr/Ca andBa/Ca ratios between birds and their food have notpreviously been measured, but the values we obtainedwere similar to those for herbivorous and carnivorousmammals at similar trophic levels. Our results provideevidence that supports the use of Sr/Ca ratios in thedetermination of human paleodiets and suggests thatSr/Ca ratios may also provide a useful tool in studiesof modern food webs. Furthermore, our findings suggestthat 90Sr from nuclear fallout will notbioaccumulate in forests and that changes in Sr/Caratios between trophic levels will need to beconsidered in some cases when using87Sr/86Sr as a tracer of calciumbiogeochemistry.
    Materialart: Digitale Medien
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  • 26
    Digitale Medien
    Digitale Medien
    Springer
    Journal of computational neuroscience 8 (2000), S. 65-86 
    ISSN: 1573-6873
    Schlagwort(e): LTP ; CaM kinase II ; calmodulin ; calcium ; dendritic spine ; dentate ; computational model ; hippocampus ; phosphorylation ; autophosphorylation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik , Medizin , Physik
    Notizen: Abstract Activation of calcium/calmodulin-dependent protein kinase II (CaMKII) by calmodulin following calcium entry into the cell is important for long-term potentiation (LTP). Here a model of calmodulin binding and trapping by CaMKII in a dendritic spine was used to estimate levels and durations of CaMKII activation following LTP-inducing tetani. The calcium signal was calcium influx through NMDA receptor channels computed in a highly detailed dentate granule cell model. Calcium could bind to calmodulin and calmodulin to CaMKII. CaMKII subunits were either free, bound with calmodulin, trapped, autonomous, or capped. Strong low-frequency tetanic input produced little calmodulin trapping or CaMKII activation. Strong high-frequency tetanic input caused large numbers of CaMKII subunits to become trapped, and CaMKII was strongly activated. Calmodulin trapping and CaMKII activation were highly dependent on tetanus frequency (particularly between 10 and 100 Hz) and were highly sensitive to relatively small changes in the calcium signal. Repetition of a short high-frequency tetanus was necessary to achieve high levels of CaMKII activation. Three stages of CaMKII activation were found in the model: a short, highly activated stage; an intermediate, moderately active stage; and a long-lasting third stage, whose duration depended on dephosphorylation rates but whose decay rate was faster at low CaMKII activation levels than at high levels. It is not clear which of these three stages is most important for LTP.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 27
    Digitale Medien
    Digitale Medien
    Springer
    Journal of bioenergetics and biomembranes 32 (2000), S. 97-104 
    ISSN: 1573-6881
    Schlagwort(e): Mitochondria ; sarcoplasmic reticulum ; calcium ; caffeine ; myocytes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Physik
    Notizen: Abstract Studies with electron microscopy have shown that sarcoplasmic reticulum (SR) andmitochondria locate close to each other in cardiac muscle cells. We investigated the hypothesis thatthis proximity results in a transient exposure of mitochondrial Ca2+ uniporter (CaUP) to highconcentrations of Ca2+ following Ca2+ release from the SR and thus an influx of Ca2+into mitochondria. Single ventricular myocytes of rat were skinned by exposing them to aphysiological solution containing saponin (0.2 mg/ml). Cytosolic Ca2+ concentration ([Ca2+]c)and mitochondrial Ca2+ concentration ([Ca2+]m) were measured with fura-2 and rhod2,respectively. Application of caffeine (10 mM) induced a concomitant increase in[Ca2+]c and [Ca2+]m.Ruthenium red, at concentrations that block CaUP but not SR release, diminished thecaffeine-induced increase in [Ca2+]m but not[Ca2+]c. In the presence of 1 mM BAPTA, a Ca2+ chelator,the caffeine-induced increase in [Ca2+]m was reduced substantially less than [Ca2+]c. Moreover,inhibition of SR Ca2+ pump with two different concentrations of thapsigargin caused anincrease in [Ca2+]m, which was related to the rate of [Ca2+]c increase. Finally, electronmicroscopy showed that sites of junctions between SR and T tubules from which Ca2+ is released,or Ca2+ release units, CRUs, are preferentially located in close proximity to mitochondria.The distance between individual SR Ca2+ release channels (feet or ryanodine receptors) isvery short, ranging between approximately 37 and 270 nm. These results are consistent withthe idea that there is a preferential coupling of Ca2+ transport from SR to mitochondria incardiac muscle cells, because of their structural proximity.
    Materialart: Digitale Medien
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  • 28
    Digitale Medien
    Digitale Medien
    Springer
    Cell biology and toxicology 16 (2000), S. 201-206 
    ISSN: 1573-6822
    Schlagwort(e): calcium ; cell cycle ; cell growth ; Ganoderma lucidum ; spores
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The effects of extracts from Ganoderma lucidum spores on the growth of human cervix uteri tumor HeLa cells as well as on the cell cycle and intracellular calcium level were investigated. Alcohol extracts were prepared from sporoderm-broken and sporoderm-nonbroken spores (termed extract I and extract II) of G. lucidum. Extract I was then subjected to silica gel chromatography to obtain extract III. Cytotoxicity was examined by means of trypan blue exclusion and MTT tests. It was found that extract I and extract III, but not extract II strongly inhibited the growth of HeLa cells, and that extract III was more effective than extract I. Moreover, extract III was shown to be capable of blocking the cell cycle at the transition from G1 to S phase and inducing a marked decrease of intracellular calcium level, determined by flow cytometry and the specific fluorescent calcium probe Fura-2, respectively. These results imply that (1) the breaking of G. lucidum spores improves the release of cytotoxic activity and (2) the effective extract might influence the cell cycle and cellular signal transduction by altering the calcium transport system.
    Materialart: Digitale Medien
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  • 29
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular neurobiology 20 (2000), S. 131-147 
    ISSN: 1573-6830
    Schlagwort(e): blood–brain barrier ; inflammation ; permeability ; electrical resistance ; calcium ; tight junction ; signal transduction ; receptor
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract 1. Unlike some interfaces between the blood and the nervous system (e.g., nerve perineurium), the brain endothelium forming the blood–brain barrier can be modulated by a range of inflammatory mediators. The mechanisms underlying this modulation are reviewed, and the implications for therapy of the brain discussed. 2. Methods for measuring blood–brain barrier permeability in situ include the use of radiolabeled tracers in parenchymal vessels and measurements of transendothelial resistance and rate of loss of fluorescent dye in single pial microvessels. In vitro studies on culture models provide details of the signal transduction mechanisms involved. 3. Routes for penetration of polar solutes across the brain endothelium include the paracellular tight junctional pathway (usually very tight) and vesicular mechanisms. Inflammatory mediators have been reported to influence both pathways, but the clearest evidence is for modulation of tight junctions. 4. In addition to the brain endothelium, cell types involved in inflammatory reactions include several closely associated cells including pericytes, astrocytes, smooth muscle, microglia, mast cells, and neurons. In situ it is often difficult to identify the site of action of a vasoactive agent. In vitro models of brain endothelium are experimentally simpler but may also lack important features generated in situ by cell:cell interaction (e.g. induction, signaling). 5. Many inflammatory agents increase both endothelial permeability and vessel diameter, together contributing to significant leak across the blood–brain barrier and cerebral edema. This review concentrates on changes in endothelial permeability by focusing on studies in which changes in vessel diameter are minimized. 6. Bradykinin (Bk)2 increases blood–brain barrier permeability by acting on B2 receptors. The downstream events reported include elevation of [Ca2+]i, activation of phospholipase A2, release of arachidonic acid, and production of free radicals, with evidence that IL-1β potentiates the actions of Bk in ischemia. 7. Serotonin (5HT) has been reported to increase blood–brain barrier permeability in some but not all studies. Where barrier opening was seen, there was evidence for activation of 5-HT2 receptors and a calcium-dependent permeability increase. 8. Histamine is one of the few central nervous system neurotransmitters found to cause consistent blood–brain barrier opening. The earlier literature was unclear, but studies of pial vessels and cultured endothelium reveal increased permeability mediated by H2 receptors and elevation of [Ca2+]i and an H1 receptor-mediated reduction in permeability coupled to an elevation of cAMP. 9. Brain endothelial cells express nucleotide receptors for ATP, UTP, and ADP, with activation causing increased blood–brain barrier permeability. The effects are mediated predominantly via a P2U (P2Y2) G-protein-coupled receptor causing an elevation of [Ca2+]i; a P2Y1 receptor acting via inhibition of adenyl cyclase has been reported in some in vitro preparations. 10. Arachidonic acid is elevated in some neural pathologies and causes gross opening of the blood–brain barrier to large molecules including proteins. There is evidence that arachidonic acid acts via generation of free radicals in the course of its metabolism by cyclooxygenase and lipoxygenase pathways. 11. The mechanisms described reveal a range of interrelated pathways by which influences from the brain side or the blood side can modulate blood–brain barrier permeability. Knowledge of the mechanisms is already being exploited for deliberate opening of the blood–brain barrier for drug delivery to the brain, and the pathways capable of reducing permeability hold promise for therapeutic treatment of inflammation and cerebral edema.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 30
    Digitale Medien
    Digitale Medien
    Springer
    Journal of bioenergetics and biomembranes 32 (2000), S. 27-33 
    ISSN: 1573-6881
    Schlagwort(e): Heart ; excitation-contraction coupling ; calcium ; mitochondrial permeability transition pore
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Physik
    Notizen: Abstract Mitochondria have been implicated in intracellular Ca2+ signaling in many cell types. Theinner mitochondrial membrane contains Ca2+-transporting proteins, which catalyze Ca2+ uptakeand extrusion. Intramitochondrial (matrix) Ca2+, in turn, regulates the activity of Krebs cycledehydrogenases and, ultimately, the rate of ATP synthesis. In the myocardium, controversyremains whether the fast cytosolic Ca2+ transients underlying excitation-contraction couplingin beating cells are rapidly transmitted into the matrix compartment or slowly integratedby the mitochondrial Ca2+ transporters. This mini-review critically summarizes the recentexperimental work in this field.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 31
    ISSN: 1573-6881
    Schlagwort(e): Mitochondria ; octylguanidine ; octylamine ; carboxyatractyloside ; permeability transition ; kidney mitochondria ; nonspecific pore ; calcium ; mitochondrial calcium ; mitochondrial membrane
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Physik
    Notizen: Abstract Mitochondrial permeability transition occurs through a Ca2+-dependent opening of atransmembrane pore, whose identity has been attributed to that of the adenine nucleotide translocase(ANT). In this work, we induced permeability transition by adding 0.5 μM carboxyatractyloside.The process was evaluated analyzing Ca2+ efflux, a drop in transmembrane electric gradient,and swelling. We found that the amphiphyllic cations octylguanidine and octylamine, at theconcentration of 100 μM, inhibited, almost completely, nonspecific membrane permeability.Hexylguanidine, hexylamine, as well as guanidine chloride and hydroxylamine failed to doso. The inhibition was reversed after the addition of 40 mM Li+, Na+ K+,Rb+, or Cs+; K+ wasthe most effective. We propose that the positive charge of the amines interact with negativecharges of membrane proteins, more likely the ADP/ATP carrier, while the alkyl chain penetratesinto the hydrophobic milieu of the inner membrane, fixing the reagent.
    Materialart: Digitale Medien
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  • 32
    ISSN: 1573-5036
    Schlagwort(e): ammonium nitrate ; calcium ; Harvard Forest ; magnesium ; nitrate leaching ; polyamines
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Polyamines (putrescine, spermidine, and spermine) are low molecular weight, open-chained, organic polycations which are found in all organisms and have been linked with stress responses in plants. The objectives of our study were to investigate the effects of chronic N additions to pine and hardwood stands at Harvard Forest, Petersham, MA on foliar polyamine and inorganic ion contents as well as soil and soil solution chemistry. Four treatment plots were established within each stand in 1988: control, low N (50 kg N ha-1 yr-1 as NH4NO3), low N + sulfur (74 kg S ha-1 yr-1 as Na2SO4), and high N (150 kg N ha-1 yr-1 as NH4NO3). All samples were analyzed for inorganic elements; foliage samples were also analyzed for polyamines and total N. In the pine stand putrescine and total N levels in the foliage were significantly higher for all N treatments as compared to the control plot. Total N content was positively correlated with polyamines in the needles (P ≤ 0.05). Both putrescine and N contents were also negatively correlated with most exchangeable cations and total elements in organic soil horizons and positively correlated with Ca and Mg in the soil solution (P ≤ 0.05). In the hardwood stand, putrescine and total N levels in the foliage were significantly higher for the high N treatment only as compared to the control plot. Here also, total foliar N content was positively correlated with polyamines (P ≤ 0.05). Unlike the case with the pine stand, in the hardwood stand foliar polyamines and N were significantly and negatively correlated with foliar total Ca, Mg, and Mn (P ≤ 0.05). Additional significant (P ≤ 0.05) relationships in hardwoods included: negative correlations between foliar polyamines and N content to exchangeable K and P and total P in the organic soil horizon; and positive correlations between foliar polyamines and N content to Mg in soil solution. With few exceptions, low N + S treatment had effects similar to the ones observed with low N alone for both stands. The changes observed in the pine stand for polyamine metabolism, N uptake, and element leaching from the soil into the soil solution in all treatment plots provide additional evidence that the pine stand is more nitrogen saturated than the hardwood stand. These results also indicate that the long-term addition of N to these stands has species specific and/or site specific effects that may in part be explained by the different land use histories of the two stands.
    Materialart: Digitale Medien
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  • 33
    ISSN: 1573-9058
    Schlagwort(e): calcium ; calcium-dependent protein kinase ; PEPC-protein kinase
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract PEP carboxylase (PEPC) in leaves of C4 plants is activated by phosphorylation of enzyme by a PEPC-protein kinase (PEPC-PK). We reevaluated the pattern of PEPC phosphorylation in leaf extracts of Amaranthus hypochondriacus. It was dependent on Ca2+, the optimum concentration of which for stimulation was 10 mM. The extent of stimulation was inhibited by 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA), a Ca2+ chelator. The inhibition by BAPTA was relieved by the addition of Ca2+ but not by the addition of Mg2+. The stimulation by Ca2+ of PEPC phosphorylation was marginally enhanced by calmodulin (CaM), but not by diacylglycerol (DAG). Phosphorylation was strongly restricted by Ca2+ or Ca2+-CaM-dependent protein kinase inhibitors. Thus phosphorylation of PEPC is Ca2+-dependent in leaves of A. hypochondriacus and a calcium-dependent protein kinase (CDPK) may modulate PEPC-PK and subsequently the phosphorylation status of PEPC.
    Materialart: Digitale Medien
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  • 34
    ISSN: 1573-8221
    Schlagwort(e): cerebellar granular cells ; sodium ; calcium ; mitochondria
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Experiments with rhodamine-123 showed that incubation of cultured cerebellar granular cells in a medium with NaCl isosmotically replaced with sucrose reduced mitochondrial membrane potential. Elimination of Ca2+ or addition of CoCl2, noncompetitive (MK-801) and competitive (APH) N-methyl-D-aspartate receptor antagonists abolished deenergizing effects of low-sodium solutions.
    Materialart: Digitale Medien
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  • 35
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of experimental biology and medicine 129 (2000), S. 36-38 
    ISSN: 1573-8221
    Schlagwort(e): GM1 ganglioside ; glutamate ; calcium ; cerebral cortex synaptosomes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Glutamate significantly increased intracellular calcium concentration, enhanced45Ca2+ entry, and activated Na+/Ca2+ exchanger in synaptosomes from rat cerebral cortex. Preincubation with GM1 ganglioside reduced the glutamate-induced increase in intracellular calcium and45Ca2+ entry. Gangliosides and glutamate stimulated Na+/Ca2+ exchanger showing additive effects.
    Materialart: Digitale Medien
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  • 36
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of experimental biology and medicine 129 (2000), S. 259-260 
    ISSN: 1573-8221
    Schlagwort(e): calcium ; stress ; benzodiazepines ; Fura-2AM
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract The effects of 5 benzodiazepines on basal and K+-induced Ca2+ concentration in synaptoneurosomes from intact and stressed C57B1/6 and BALB/c mice were studiedin vitro. Membrane depolarization induced by low KCl concentrations produced different effects on Ca2+ accumulation by synaptoneurosomes from two mouse strains. Benzodiazepines appliedin vitro exerted no effects on Ca2+ influx. In synaptoneurosomes from both C57B1/6 and BALB/c mice exposed to emotional stress diazepam in a dose of 5 mg/kg reduced the basal and K+-induced Ca2+ accumulation.
    Materialart: Digitale Medien
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  • 37
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of experimental biology and medicine 129 (2000), S. 158-160 
    ISSN: 1573-8221
    Schlagwort(e): doxorubicin ; brain mitochondria ; calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract Calcium capacity of rat brain mitochondria oxidizing succinate and NAD-dependent substrates was reduced after incubation with doxorubicin as a result of decreased energy production due to inhibition of SDH and transamination processes.
    Materialart: Digitale Medien
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  • 38
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 45 (1989), S. 175-177 
    ISSN: 1420-9071
    Schlagwort(e): Dystrophin ; calcium ; skeletal muscle ; muscular dystrophy
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: 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.
    Materialart: Digitale Medien
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  • 39
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 45 (1989), S. 305-306 
    ISSN: 1420-9071
    Schlagwort(e): Baboon ; 133xenon ; cerebral blood flow ; cerebrovascular resistance ; autoregulation ; nimodipine ; calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: 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.
    Materialart: Digitale Medien
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  • 40
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 45 (1989), S. 377-378 
    ISSN: 1420-9071
    Schlagwort(e): Chromatoid body ; spermatids ; calcium ; microtubules ; morphology ; pyroantimonate ; rat
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 41
    Digitale Medien
    Digitale Medien
    Springer
    Mycopathologia 108 (1989), S. 47-54 
    ISSN: 1573-0832
    Schlagwort(e): Candida albicans ; dimorphism ; yeast-mycelium transition ; calcium ; calmodulin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: Abstract A yeast-mycelium (Y-M) transition of Candida albicans (3153A) was induced by 1.5 mM CaCl2 · 2H2O in defined liquid medium, pH 7, at 25 °C. Germ tube formation was detected after approximately 8 h and peaks of maximum germination occurred at approximately 20 h in all experimental treatments. Non-toxic concentrations of the calmodulin inhibitor R24571 almost completely suppressed germ tube formation whereas trifluoperazine (TFP) and the Ca2+ ionophore A23187 were only about half as effective. Further Ca2+ addition failed to reverse the inhibitory effect of R24571 and induced only about 10% of the cells inhibited by TFP or A23187 to germinate.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 42
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 103-108 
    ISSN: 1573-4919
    Schlagwort(e): heart ; relaxation ; calcium ; sodium-calcium exchange
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Transsarcolemmal calcium movements are closely related to force generation in the heart. It is important to understand the transport pathways that control these movements of calcium across the sarcolemmal membrane. In the normal, beating heart, sodium-calcium exchange appears to be an important mechanism for the extrusion of calcium from the cell. The kinetics of this exchange are dependent upon the characteristics of the cell action potential. Calcium efflux via sodium-calcium exchange may be sufficient to balance calcium entry through calcium channels during the action potential.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 43
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 97-102 
    ISSN: 1573-4919
    Schlagwort(e): calcium ; sodium ; fura-2
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Membrane currents and changes in intracellular calcium ion concentration ([Ca2+]i) have been recorded that can be attributed to the operation of an electrogenic, voltage-dependent sodium-calcium (Na-Ca) exchanger in mammalian heart cells. Single guinea-pig ventricular myocytes under voltage clamp were perfused internally with the fluorescent Ca2+-indicator, fura-2, and changes in [Ca2+]i and membrane current that resulted from Na-Ca exchange were isolated through the use of various organic channel blockers (verapamil, TTX), impermeant ions (Cs+, Ni2+), and inhibitors of sarcoplasmic reticulum (ryanodine). The I-V relation of Na-Ca exchange was obtained from the Ni2+-sensitive current elicited by ramp repolarization from +90 mV to −80 mV. Ramps were sufficiently rapid that little change in [Ca2+]i occured during the ramp. The (constant) [Ca2+]i during the ramp was varied over the range 100 nM to 1000 nM by varying the amplitude and duration of a pre-pulse to the ramp. The reversal potential of the Ni2+-sensitive ramp current varied linearly with 1n([Ca2+])i. The I-V relations at different [Ca2+]i over the range −60 mV to +140 mV were in reasonable accord with the predictions of a simple, simultaneous scheme of Na-Ca exchange, on the basis that only [Ca2+]i had changed. The relationship between [Ca2+]i and current at a constant membrane voltage was also in accord with this scheme. We suggest that Ca2+-fluxes through the exchanger during the cardiac action potential can be understood quantitatively by considering the binding of Ca2+ to the exchanger during the [Ca2+]i-transient and the effects of membrane voltage on the exchanger.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 44
    ISSN: 1573-4919
    Schlagwort(e): calcium ; heart ; sarcoplasmic reticulum ; excitation-contraction coupling
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract Recent studies correlating the calcium current with, respectively, the clamp-imposed voltage and the calcium current in intact isolated mammalian cardiac myocytes are reviewed. The major findings are the following: [1] With the exception of one group, all investigators agree that a calcium transient is never observed in the absence of a calcium current. In addition, there is a good correlation between voltage dependence of the calcium current and that of the calcium transient, although this correlation may vary among the cardiac tissues from different animal species. [2] Repolarization clamp pulses from highly positive potentials produce a ‘tail current’ which is associated with a ‘tail calcium transient’. [3] The calcium transient is inhibited when the calcium current is blocked by calcium deprivation or substitution, or by the addition of calcium current antagonists, despite the fact that sarcoplasmic reticulum still contains calcium that can be released by caffeine (with inhibition of this release by ryanodine). These three findings are strongly in favor of a calcium-induced release of calcium and against the hypothesis of charge-movement-coupled release of calcium from the sarcoplasmic reticulum. [4] The only finding that would be more in favor of the latter hypothesis (although till reconciliable with the former) is that repolarization occurring before the rapid rise of calcium transient is complete curtails the calcium transient. Thus, the possibility that charge movement might somehow regulate calcium-induced release of calcium cannot be excluded.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 45
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 169-173 
    ISSN: 1573-4919
    Schlagwort(e): pH ; calcium ; heart muscle
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The contractile response to acidosis is the final product of a number of different changes in the excitation-contraction coupling pathway: (i) Cai increases and subsequently decreases during acidosis; (ii) the action potential becomes longer; (iii) the sensitivity of the contractile proteins to Ca2+ decreases. The increase of Cai and the lengthening of the action potential may help to maintain contractile function, although this advantage may be offset if spontaneous Ca2− release from the s.r. occurs, secondary to the increase of Cai. The recovery of force shown in figure 1 occurs at a time when the calcium transient is decreasing, and therefore represents an increasing sensitivity of the contractile proteins to Cai, probably due to a recovery of intracellular pH(6), although it is also possible that a disappearance of spontaneous Ca2+ releases from the s.r. may be contributing [2].
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 46
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 127-133 
    ISSN: 1573-4919
    Schlagwort(e): mitochondria ; sarcoplasmic reticulum ; calcium ; myocytes ; caffeine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The possible contribution of mitochondrial Ca2+ accumulation and release to contractile phenomena has been investigated. Two intracellular fractions of Ca2+ sequestration can be identified in cardiac myocytes, one ascribed to mitochondria. Two modes of Ca2+ transport exist within the mitochondrial fraction, one dependent upon mitochondrial respiration and the other upon extramitochondrial [Na+]. Experiments with trabeculae show that under appropriate conditions, the rate of relaxation and the amount of tension developed is dependent on these two modes of Ca2+ transport. A model is presented quantifying the contribution of the mitochondria to relaxation.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 47
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 89 (1989), S. 109-113 
    ISSN: 1573-4919
    Schlagwort(e): heart muscle ; calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The role of Ca2+ in the initiation and maintenance of contraction has been extensively studies. Many of these studies have focused on how Ca2+ influx and efflux affect cytoplasmic Ca2+ (Cai) and, therefore, contraction in cardiac muscle. However, it has recently become apparent that Cai itself may play a major role in the control of Ca2+ influx and efflux from cardiac muscle. Here we review current ideas on the mechanisms underlying Ca2+ homeostasis in cardiac muscle, with specific attention to how Cai may control Ca2+ influx, both under normal and pathological conditions.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 48
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 90 (1989), S. 155-164 
    ISSN: 1573-4919
    Schlagwort(e): polyvanadate ; mitochondria ; calcium ; pyruvate dehydrogenase ; receptors
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Summary Mitochondria isolated from the livers of rats administered with sodium meta-, ortho-, or polyvanadate, but not vanadyl sulphate, exhibited enhanced Ca2+ — stimulated respiration and uptake of calcium. These effects were shown also by mitochondria isolated from livers perfused with polyvanadate. The concentration of acid-soluble calcium decreased significantly in the mitochondrial fraction on vanadate treatment, while that in the cytosol showed a corresponding increase. Phenoxybenzamine, an antagonist to a-adrenergic receptors, effectively inhibited vanadate-induced Ca2+ mobilization, but surgical sympathectomy was without effect. This is the first demonstration of vanadate mimicking α-adrenergic agonists in vivo.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 49
    Digitale Medien
    Digitale Medien
    Springer
    Bioscience reports 9 (1989), S. 99-109 
    ISSN: 1573-4935
    Schlagwort(e): mast cells ; exocytosis ; G-protein ; GE ; calcium ; ATP
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract ATP is not required for exocytosis from permeabilised mast cells, and therefore there is no direct role for protein phosphorylation in the late stages of the activation pathway. We have measured the timecourse of exocytosis from permeabilised cells triggered to release hexosaminidase following addition of Ca2+ to cells equilibrated for 2 min with GTP-γ-S. If ATP is included at the time of permeabilisation, then exocytosis commences after a delay, the duration of which depends on the square root of the product [Ca2+][GTP-γ-S], and which may extend to beyond 3 min. When ATP is excluded then the maximal rate of exocytosis is established within 3 secs of completing the effector combination. These results suggest that the achievement of a new steady-state, induced by Ca2+ and GTP-γ-S, and required for exocytosis is inhibited by ATP. From this we conclude that dephosphorylation of an unknown regulator protein may comprise a step in the exocytotic pathway.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 50
    Digitale Medien
    Digitale Medien
    Springer
    Bioscience reports 9 (1989), S. 243-252 
    ISSN: 1573-4935
    Schlagwort(e): secretion ; exocytosis ; chromaffin cell ; calcium ; bradykinin ; angiotensin II, muscarinic
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Bradykinin, angiotensin II and a mascarnic agonist, acetyl-B-methacholine (methacholine) were all found to elict catecholamine release from cultured bovine adrenal chromaffin cells. Bradykinin was the most potent of these secretagogues and methacholine the weakest, with angiotenin II intermediate in efficacy. All three secretagogues were much less effective than nicotinic stimulation. The three secretagogues all produced a rise in cytoplasmic free calcium concentration ([Ca2+]i), measured with the fluorescent indicator fura2, which was partially independent of external calcium. In the case of bradykinin the full rise in ([Ca2+]i) may involve a component of calcium entry in addition to release of calcium from an internal store. Secretion was also found to be partially independent of external calcium. The different efficacies of the three secretagogues in elicting secretion were correlated with the rise in ([Ca2+]i) produced. The differeing efficacies of the three secretagogues may be due to the extent of release of calcium from an intracellular store which itself is less effective in eliciting secretion than a rise in [Ca2+]i following calcium entry due to nicotine. Bradykinin also stimulates calcium entry, and this may increase the efficacy of the initial rise in [Ca2+]i. Treatment with pertussis toxin resulted in an enhancement of secretion in response to all of the secretagogues.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 51
    Digitale Medien
    Digitale Medien
    Springer
    The journal of membrane biology 107 (1989), S. 179-188 
    ISSN: 1432-1424
    Schlagwort(e): stretch-activated channel ; calcium ; oocyte ; development ; patch clamp ; tunicate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 52
    ISSN: 1432-1424
    Schlagwort(e): calcium ; calmodulin ; absorption ; ileum ; brush-border vesicle ; phosphorylation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 53
    Digitale Medien
    Digitale Medien
    Springer
    The journal of membrane biology 110 (1989), S. 49-55 
    ISSN: 1432-1424
    Schlagwort(e): loop of Henle ; potassium secretion ; channels ; acid/base balance ; thick ascending limb ; calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 54
    Digitale Medien
    Digitale Medien
    Springer
    The journal of membrane biology 110 (1989), S. 19-28 
    ISSN: 1432-1424
    Schlagwort(e): colon ; ion transport ; ion channel ; cyclic nucleotides ; calcium ; potassium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 55
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of experimental biology and medicine 108 (1989), S. 1634-1636 
    ISSN: 1573-8221
    Schlagwort(e): c-src locus ; calcium ; Na+, K+-cotransport
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 56
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular neurobiology 9 (1989), S. 141-178 
    ISSN: 1573-6830
    Schlagwort(e): 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
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 57
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 115 (1989), S. 53-58 
    ISSN: 1573-5036
    Schlagwort(e): ammonia volatilization ; calcium ; magnesium ; manure
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 58
    ISSN: 1573-5036
    Schlagwort(e): aluminium ; calcium ; manganese ; needles ; soil solution ; spruce ; toxicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 59
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 119 (1989), S. 186-190 
    ISSN: 1573-5036
    Schlagwort(e): ammonium ; calcium ; forest soil ; ion exchange resin ; magnesium ; manganese ; nitrate ; phosphorus ; soil analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
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  • 60
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 119 (1989), S. 181-185 
    ISSN: 1573-5036
    Schlagwort(e): aluminium toxicity ; calcium ; honeylocust ; root biomass ; root branching ; soil acidification
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
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  • 61
    Digitale Medien
    Digitale Medien
    Springer
    Bioscience reports 9 (1989), S. 497-502 
    ISSN: 1573-4935
    Schlagwort(e): calcium ; phosphatidate ; DPH ; phase fluorometry ; distributional analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Calcium interaction with phospholipid membranes containing phosphatidic acid is studied by multifrequency phase fluorometry, using DPH as fluorescent molecule. DPH decay is analysed by a continuous distribution of lifetimes. The results suggest an increase of membrane heterogeneity at low calcium concentrations, without changes in the polarity of the environment surrounding the probe.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 62
    Digitale Medien
    Digitale Medien
    Springer
    Journal of pharmacokinetics and pharmacodynamics 17 (1989), S. 631-644 
    ISSN: 1573-8744
    Schlagwort(e): calcium ; absorption ; efficiency ; dosing ; regimens
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract The absorption of calcium involves a saturable (active) and a nonsaturable (passive) component. The work of several investigators indicates that an inverse relationship exists between calcium intake and absorption efficiency. Human calcium absorption data from the literature were analyzed using a model which included both an active and a passive absorption component. Simulations were provided to illustrate the suitability of this model, and another previously reported model, to fit the data and to estimate the absorption efficiency of calcium when using different dosing regimens. Comparisons of the values predicted in this study with some literature values are provided and some assumptions and potential limitations associated with the use of this method are discussed. The division of the daily dose into equal increments taken at equally spaced intervals over the course of the day is recommended as a useful procedure for increasing the absorption efficiency and efficacy of calcium.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 63
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 113 (1989), S. 3-11 
    ISSN: 1573-5036
    Schlagwort(e): calcium ; chlorine ; ion selectivity ; injury ; Picea ; potassium ; retranslocation ; sodium ; uptake
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
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  • 64
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 176-177 (1989), S. 323-329 
    ISSN: 1573-5117
    Schlagwort(e): strontium ; calcium ; coprecipitation ; Lake Constance
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The contents of Sr and Ca were measured weekly in Lake Constance in 1986. Epilimnetic concentrations of Ca changed between 1.30 × 10-3 mol l-1 (during homothermy) and 0.9 × 10 -3 mol l-1 (during thermal stratification). The seasonal fluctuations of Ca were correlated with those of Sr (between 4.61 and 5.36 μmol l-1). The epilimnion was permanently oversaturated with respect to calcite but not with respect to SrCO3. Analysis of the settling process by use of sedimentation traps revealed two short episodes of very high authigenic settling fluxes of CaCO3, triggered by phytoplankton diatoms. Seasonal changes of the Ca contents (between 4.1 and 30.7 percent of the dry weight) and of the Sr concentrations (from 12 to 75 × 10-3 percent) in the settling material were closely correlated. This suggests a coprecipitation mechanism with a nearly constant stoichiometry of (atoms Sr/atoms Ca) × 1000 of 0.84. Coprecipitation of Sr or Ca with organic matter was insignificant. In the hypolimnion some Sr and Ca were released from the settling material. These results strongly suggest that the cycle of Sr in Lake Constance is driven predominantly by coprecipitation with calcite. The principal chemical mechanisms leading to coprecipitation are discussed.
    Materialart: Digitale Medien
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  • 65
    ISSN: 1573-5117
    Schlagwort(e): reservoir ; phytoplanktonic particulate phosphorus ; regulation ; calcium ; magnesium ; multiple regression analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract At the heads of two river reservoirs, the Ishitegawa Dam and the Nomura Dam Reservoirs in Japan, the concentrations of phytoplanktonic particulate phosphorus (PP) were compared with those of dissolved calcium (Ca) and magnesium (Mg), using multiple regression analyses on the data taken from samples which registered more than 6.0 µg l−1 in chlorophyll a concentration. Of the 27 monthly samples, 16 from the Ishitegawa Reservoir and 17 from the Nomura Reservoir were used. A significant regression line, logPP = k 1F + k 2, was obtained, where k 1 (〉 0) and k 2 were constants and F (named the Ca-Mg index) consisted of log(Ca/Mg) − 0.5 log(ca + Mg) in mol concentration in Ca and Mg, in common with the two reservoirs (r 2 = 0.730 & 0.913).
    Materialart: Digitale Medien
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  • 66
    Digitale Medien
    Digitale Medien
    Springer
    Fish physiology and biochemistry 7 (1989), S. 323-329 
    ISSN: 1573-5168
    Schlagwort(e): renin release ; aglomerular teleost ; toadfish ; isoproterenol ; cyclic AMP ; cyclic GMP ; calcium ; calcium channel ; K+ depolarization ; baroreceptor ; calcium channel antagonist
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 67
    Digitale Medien
    Digitale Medien
    Springer
    Fish physiology and biochemistry 7 (1989), S. 367-374 
    ISSN: 1573-5168
    Schlagwort(e): teleocalcin ; calcium ; corpuscles of Stannius ; gill function ; prolactin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 68
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 116 (1989), S. 111-114 
    ISSN: 1573-5036
    Schlagwort(e): calcium ; moisture ; peanut ; pod zone ; reproductive growth
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
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  • 69
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 117 (1989), S. 67-74 
    ISSN: 1573-5036
    Schlagwort(e): bacterial adsorption ; calcium ; magnesium ; Medicago sativa ; pH ; Rhizobium meliloti ; root surface
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 70
    Digitale Medien
    Digitale Medien
    Springer
    Antonie van Leeuwenhoek 56 (1989), S. 191-199 
    ISSN: 1572-9699
    Schlagwort(e): calcium ; conidiation ; nucleotides ; nucleotide charges ; Penicillium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
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  • 71
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 113 (1989), S. 229-235 
    ISSN: 1573-5036
    Schlagwort(e): aluminium ; calcium ; foliar analysis ; magnesium ; nitrogen ; nutritional disturbance ; Pinus sylvestris L. ; potassium ; soil analysis
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 72
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 120 (1989), S. 203-211 
    ISSN: 1573-5036
    Schlagwort(e): calcium ; chlorine ; climate ; injury ; Picea ; rating ; sodium ; soil
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 73
    ISSN: 1573-904X
    Schlagwort(e): pancreatic lipase ; lipase ; lipolysis ; triglycerides ; kinetics ; mechanism ; calcium ; bile salts ; lecithin ; emulsions
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie
    Notizen: Abstract Lecithin-stabilized triglyceride emulsions are subject to hydrolysis by pancreatic lipase. The time profiles of these reactions are characterized by a lag-phase and a zero-order phase. Lag phases are more pronounced with long-chain triglycerides. Ca2+ is effective in reducing the lag-phase and activating lipase. Kinetic analysis of the reactions suggests that, like previous findings by others, taurodeoxycholate (TDC) micellar solutions combine with the lipase–colipase complex to form another catalytically active enzyme form. This enzyme form exhibits reduced activity in the absence of Ca2+. In the presence of Ca2+ the mixed micelle–lipase complex becomes more active and opens a new pathway for lipolysis. It is suggested that this enzyme form can bind more easily to interfaces with different physicochemical properties. Under these conditions, Ca2+ activates the lipolysis of short-, medium-, and long-chain triglycerides by a similar mechanism. Maximum activities were measured in the presence of approximately 6 mM TDC and 30 mM Ca2+. The experimental conditions approximate the physiological conditions in the gastrointestinal tract since all of the factors studied here have been reported to be necessary for in vivo lipolysis and/or absorption of triglycerides. A mechanistic model for lipolysis in the presence of Ca2+ and the bile salt TDC is proposed which accounts for most of the experimental observations in a quantitative manner.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 74
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of experimental biology and medicine 107 (1989), S. 574-577 
    ISSN: 1573-8221
    Schlagwort(e): epidermocytes ; calcium ; multiplication ; autoradiographic investigation
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 75
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of experimental biology and medicine 107 (1989), S. 3-6 
    ISSN: 1573-8221
    Schlagwort(e): hypoxia ; coronary spasm ; calcium ; sarcoplasmic reticulum ; inositol-1,4,5-triphosphate
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 76
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 44 (1988), S. 101-104 
    ISSN: 1420-9071
    Schlagwort(e): Platelets ; calcium ; phospholipase A2 ; G-proteins ; arachidonic acid
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 77
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 44 (1988), S. 657-666 
    ISSN: 1420-9071
    Schlagwort(e): 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
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: 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.
    Materialart: Digitale Medien
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  • 78
    ISSN: 1573-0867
    Schlagwort(e): Potassium ; magnesium ; calcium ; aluminium ; exchange coefficient ; equilibrium activity ratio ; organic matter ; bonding strength
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract The influence of Ca(OH)2 on K and Mg exchange equilibria in three New Zealand soils was studied. Calcium hydroxide was mixed with each soil to raise the pH to about 6 or 7. For each Ca(OH)2 treatment, K and Mg exchange isotherms were determined, from which the equilibrium activity ratios were derived. Exchange coefficients and solution activity ratios were calculated according to the Gapon convention. The addition of Ca(OH)2 produced varying effects in the Gapon exchange coefficient for both K and Mg. The magnitude and direction of change in the exchange coefficient were related to the cation initially dominating the exchange sites, rate of Ca(OH)2 addition, soil colloids contributing to the CEC and specific interactions of Ca with these soil colloids. Addition of Ca(OH)2 reduced the equilibrium activity ratio of all soils. Changes in the bonding strength of K and Mg with increasing CEC were suggested as a possible mechanism for this decrease.
    Materialart: Digitale Medien
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  • 79
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular life sciences 44 (1988), S. 936-944 
    ISSN: 1420-9071
    Schlagwort(e): Contractile system ; fetus ; premature myocardium ; calcium ; sarcoplasmic reticulum ; contractile protein ; sarcolemma
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Notizen: 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.
    Materialart: Digitale Medien
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  • 80
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 82 (1988), S. 67-73 
    ISSN: 1573-4919
    Schlagwort(e): neurotransmitter control ; secretion ; exocrine ; salivary gland ; calcium ; ATP-dependent calcium transport
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Summary Salivary gland fluid secretion following neurotransmitter stimulation is Ca2+-dependent. We have studied the control of cellular Ca2+ following secretory stimuli in rat parotid gland acinar cells. After muscarinic-cholinergic receptor activation, cytosolic Ca2+ is elevated 4–5 fold, due to both intracellular Ca2+ pool mobilization and extracellular Ca2+ entry. Fluid movement ensues due to the Ca2+-activated enhancement of membrane permeability to K+ and Cl−. Basal cytosolic Ca2+ levels are tightly controlled at ∼150–200 nM through the action of high affinity and high capacity ATP-dependent Ca2+ transporters in the basolateral and endoplasmic reticulum membranes. Activity of these Ca2+ transporters can be modulated to facilitate rapid responsiveness and a sustained fluid secretory response necessary for alimentary function.
    Materialart: Digitale Medien
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  • 81
    Digitale Medien
    Digitale Medien
    Springer
    Molecular and cellular biochemistry 84 (1988), S. 97-103 
    ISSN: 1573-4919
    Schlagwort(e): neutrophils ; A23187 ; lasalocid ; calcium ; superoxide ; chemotactic peptide
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Summary Effects of Ca2+ ionophores, A23187 and lasalocid, on superoxide anion generation by chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine methyl ester, in rabbit peritoneal exudate neutrophils were studied. The ionophores by themselves did not activate superoxide anion generation in these neutrophils. When preincubated with the cells for 2 min, both the ionophores inhibited superoxide generation induced by chemotactic peptide. The inhibition was present even in the absence of extracellular Ca2+ and the inhibition was better then. Lasalocid produces a dose-dependent chlortetracycline fluorescence decrease response in neutrophils loaded with chlortetracycline. This response is independent of extracellular Ca2+ concentration and is related to release of Ca2+ from intracellular storage sites. The dose-range at which lasalocid gives this response is same as the dose-range at which it causes inhibition of superoxide response. It may be concluded that the inhibition of superoxide generation by these ionophores is correlated to intracellular Ca2+ modulation.
    Materialart: Digitale Medien
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  • 82
    ISSN: 1573-4919
    Schlagwort(e): bladder ; muscarinic stimulation ; metabolism ; bethanecol ; calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie , Medizin
    Notizen: Abstract The calcium dependence of contraction and NADH flurorescence was investigated in rabbit bladder stimulated with bethanechol or KCl. The absence of calcium in the bathing solution induced a rightward shift in the dose response to bethanechol for both contraction and NADH flurorescence. The contractile response was shifted to a greater degree than the fluorescence response and the maximal response to bethanechol was reduced by 80% for contraction but only 20% for NADH fluorescence. This rightward shift was also induced by the benzothiazepine calcium antagonist diltiazem (200 μM) and again the contractile response was shifted significantly more than the fluorescence response. The combination of zero calcium and 200 μM diltiazem virtually abolished contractions but only inhibited the NADH fluorescence by 65% at maximally effective bethanechol concentrations. Unlike the effect of diltiazem on the response to bethanechol, diltiazem (200 μM) shifted both the contraction and fluorescence curves to the right equally in response to KCl stimulation. These results indicate that a metabolic response to muscarinic stimulation (decreased NADH) can occur in the absence of any observable contractile response. This metabolic response may be due to post receptor signal processing events. For KCl stimulation, the NADH response is probably secondary to and a result of the contractile response.
    Materialart: Digitale Medien
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  • 83
    Digitale Medien
    Digitale Medien
    Springer
    Bioscience reports 8 (1988), S. 579-583 
    ISSN: 1573-4935
    Schlagwort(e): calcium ; zinc ; membrane protection
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Certain cytotoxic agents damage cells by the induction of pores across their plasma membrane. Ca2+ and Zn2+ protect against such damage by promoting pore closure. Zn2+ may play a beneficial role in this regard in certain disease states.
    Materialart: Digitale Medien
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  • 84
    Digitale Medien
    Digitale Medien
    Springer
    Bioscience reports 8 (1988), S. 27-33 
    ISSN: 1573-4935
    Schlagwort(e): cystic fibrosis ; chloride transport ; exocytosis ; calcium ; calmodulin ; B-adrenergic ; cyclic AMP
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract A biochemical link is proposed between recent observations on defective regulation of Cl− transport in CF respiratory epithelial cells and studies showing altered biological activity of calmodulin in exocrine glands from CF patients. A consensus is emerging that defective β-adrenergic secretory responsiveness in CF cells is caused by a defect in a regulator protein at a site distal to cyclic AMP formation. Our results indicate that this protein might be a specific calmodulin acceptor protein which modifies the activity of calmodulin in epithelial cells. Alteration in Ca2+/calmodulin dependent regulation of Cl− transport and protein secretion could explain (i) alterations in Ca2+ homeostasis seen in CF, (ii) defective β-adrenergic responses of CF cells, and (iii) the observed inability of cyclic AMP (acting via its specific protein kinase, A-kinase) to open apical membrane Cl− channels in CF epithelial cells. Most of the physiological abnormalities of CF including elevated sweat electrolytes and hyperviscous mucus can be explained on this basis.
    Materialart: Digitale Medien
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  • 85
    Digitale Medien
    Digitale Medien
    Springer
    Bioscience reports 8 (1988), S. 335-343 
    ISSN: 1573-4935
    Schlagwort(e): calcium ; exocytosis ; sea urchin egg ; phosphoinositide ; diacylglycerol
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: Abstract Micromolar calcium ion concentrations stimulate exocytosis in a reconstituted system made by recombining in the plasma membrane and cortical secretory granules of the sea urchin egg. The isolated cortical granules are unaffected by calcium concentrations up to 1 mM, nor do granule aggregates undergo any mutual fusion at this concentration. Both isolated plasma membrane and cortical granules can be pretreated with 1 mM Ca before reconstitution without affecting the subsequent exocytosis of the reconstituted system in response to micromolar calcium concentrations. On reconstitution, aggregated cortical granules will fuse with one another in response to micromolar calcium provided that one of their number is in contact with the plasma membrane. If exocytosis involves the generation of lipid fusogens, then these results suggest that the calcium-stimulated production of a fusogen can occur only when contiguity exists between cortical granules and plasma membrane. They also suggest that a substance involved in exocytosis can diffuse and cause piggy-back fusion of secretory granules that are in contact with the plasma membrane. Our results are also consistent with a scheme in which calcium ions cause a reversible, allosteric activation of an exocytotic protein.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 86
    Digitale Medien
    Digitale Medien
    Springer
    The journal of membrane biology 105 (1988), S. 207-219 
    ISSN: 1432-1424
    Schlagwort(e): choroid plexus ; brush border membrane ; Ca2+-activated K+ channels ; calcium ; barium ; TEA ; intracellular pH ; cerebrospinal fluid secretion
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 87
    Digitale Medien
    Digitale Medien
    Springer
    The journal of membrane biology 105 (1988), S. 221-231 
    ISSN: 1432-1424
    Schlagwort(e): choroid plexus ; calcium-activated potassium currents ; cerebrospinal fluid secretion ; calcium ; delayed currents ; patch clamp
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 88
    Digitale Medien
    Digitale Medien
    Springer
    The journal of membrane biology 101 (1988), S. 199-207 
    ISSN: 1432-1424
    Schlagwort(e): exocytosis ; membrane fusion ; secretion ; calcium ; sea urchin egg ; cortical granule
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 89
    Digitale Medien
    Digitale Medien
    Springer
    The journal of membrane biology 101 (1988), S. 33-41 
    ISSN: 1432-1424
    Schlagwort(e): electric current ; protons ; Neurospora crassa ; pH gradient ; H+-ATPase ; calcium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 90
    Digitale Medien
    Digitale Medien
    Springer
    The journal of membrane biology 104 (1988), S. 21-34 
    ISSN: 1432-1424
    Schlagwort(e): exocytosis ; secretion ; calcium ; protein kinase C ; adrenal medulla ; catecholamine
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Chemie und Pharmazie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 91
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of experimental biology and medicine 106 (1988), S. 1699-1702 
    ISSN: 1573-8221
    Schlagwort(e): platelets ; aggregation ; refractoriness ; calcium ; ADP
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 92
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of experimental biology and medicine 105 (1988), S. 181-183 
    ISSN: 1573-8221
    Schlagwort(e): diabetes mellitus ; calcium ; anticalcitonin antibodies ; reaction of enzyme-labeled antibodies
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 93
    Digitale Medien
    Digitale Medien
    Springer
    Bulletin of experimental biology and medicine 105 (1988), S. 244-247 
    ISSN: 1573-8221
    Schlagwort(e): biorhythms ; calcium ; immunization ; helio-geophysical rhythms
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie , Medizin
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 94
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular neurobiology 8 (1988), S. 115-128 
    ISSN: 1573-6830
    Schlagwort(e): adrenal gland ; chromaffin cells ; phorbol ester ; digitonin ; secretion ; calcium ; trypsin
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 95
    Digitale Medien
    Digitale Medien
    Springer
    Cellular and molecular neurobiology 8 (1988), S. 129-138 
    ISSN: 1573-6830
    Schlagwort(e): GTP-binding proteins ; calcium ; exocytosis ; guanine nucleotides ; adrenocorticotropic hormone (ACTH) ; AtT-20 cells
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: 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).
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 96
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 106 (1988), S. 263-268 
    ISSN: 1573-5036
    Schlagwort(e): calcium ; lipid ; peanut(Arachis hypogaea) ; potassium ; starch
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 97
    ISSN: 1573-5036
    Schlagwort(e): calcium ; chlorophyll ; Cucumis melo L. ; magnesium ; plant growth ; potassium
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 98
    Digitale Medien
    Digitale Medien
    Springer
    Plant and soil 105 (1988), S. 25-32 
    ISSN: 1573-5036
    Schlagwort(e): calcium ; cultivars ; foliar injury ; Glycine max ; phosphate uptake ; sodium ; solution cultures ; soybean ; toxicity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: Abstract Many soybean [Glycine max (L.) Merr.] genotypes that are grown in solution cultures are highly sensitive to the combination of both salinity and inorganic phosphate (Pi) in the substrate. This effect has been observed on numerous occasions on plants grown in a saline medium that contained a substantial amount of Ca (i.e., CaCl2/NaCl=0.5 on a molar basis). Because Ca is important in regulating ion transport and membrane permeability, solution culture experiments were designed to examine the effects of various concentrations of Pi and ratios of CaCl2/NaCl (0 to 0.5 on a molar basis) at a constant osmotic potential (−0.34 MPa) on this adverse interaction. Four soybean cultivars (‘Lee’, ‘Lee 74’ ‘Clark’ and ‘Clark 63’) were tested. No adverse salinity x Pi interaction was found on Lee at any ratio and leaf P and Cl were maintained below 300 and 200 mmol kg−1 dry wt, respectively. Clark, Clark 63 and Lee 74 soybean plants, on the other hand, were severely injured by solution salinity (−0.34 MPa osmotic potential) when substrate Pi was ≥0.12 mM. Reduced substrate Ca did not intensify the salinity x Pi interaction. On the contrary, the onset of injury was hastened and more severe with increased CaCl2/NaCl ratios in isotonic solutions. Shoot and root growth rates decreased as injury increased. Leaf P concentrations from these cultivars grown in saline solutions with 0.12 mM Pi were excessive (〉600 mmol kg−1 dry wt) compared with concentrations commonly found in soybean leaf tissue yet they were independent of the severity of injury. Since leaf Cl increased wiht increased CaCl2/NaCl ratio, we suspect that the severity of foliar injury was related to the combined effects of excessive P and Cl within the tissue. Lee 74, the only injured cultivar examined that excluded Cl from its leaves, was less sensitive than either Clark cultivar and its injury was characteristically different. Other ion interactions were reported that may have played a role in injury susceptibility.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 99
    Digitale Medien
    Digitale Medien
    Springer
    Hydrobiologia 169 (1988), S. 23-30 
    ISSN: 1573-5117
    Schlagwort(e): deepwater rice ; water chemistry ; diel change ; oxygen ; anoxic ; calcium ; Eichhornia
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The chemistry of water in fields at two Bangladesh deepwater rice locations is compared. Although Manikganj lies in the Jamuna (-Brahmaputra) floodplain and Sonargaon in the old Meghna floodplain, their chemistries during the flood season are similar, apart from higher Mg % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGadiiEayaara% aaaa!3703!\[\bar x\]: 3.57 v.1.8 mg 1−1), Ca (% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGadiiEayaara% aaaa!3703!\[\bar x\]: 13.1 v.4.5 mg l−1 ), pH and total alkalinity at the former. Diel changes in oxygen and sometimes also pH were evident 10 cm below the surface in deepwater rice fields, but such changes were typically much greater in fallow fields. Measurements made between 1400 and 1600 h in a range of habitats showed a trend for high pH values to be associated with high O2 values. Water in Eichhornia beds had the lowest values, deepwater rice fields were intermediate and fallow fields and other open areas typically had the highest values. O2 concentrations in excess of 15 mg l−1 and pH values of about 10.0 sometimes occurred in fallow fields with dense masses of submerged plants and loosely associated algal flocs. There was an increasing tendency for the water to become anoxic towards the end of the season and water 10 cm above the bottom was almost or entirely anoxic in deepwater rice fields at both locations over the whole 24-h period of 4/5 October, at a time when the depth of the water was starting to drop. Nitrite increased and sulphate decreased at both locations towards the end of the season.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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  • 100
    Digitale Medien
    Digitale Medien
    Springer
    New forests 2 (1988), S. 173-193 
    ISSN: 1573-5095
    Schlagwort(e): salinity ; calcium ; seedling nutrition ; lime-induced chlorosis ; fertilization ; soil management
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Land- und Forstwirtschaft, Gartenbau, Fischereiwirtschaft, Hauswirtschaft
    Notizen: 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.
    Materialart: Digitale Medien
    Standort Signatur Erwartet Verfügbarkeit
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