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  • calcium  (6)
  • Springer  (6)
  • 2005-2009
  • 2000-2004
  • 1985-1989  (6)
  • 1980-1984
  • 1975-1979
  • 1965-1969
  • 1988  (6)
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  • 2005-2009
  • 2000-2004
  • 1985-1989  (6)
  • 1980-1984
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  • 1
    Digitale Medien
    Digitale Medien
    Ca2+-activated K+ channels in the apical membrane ofNecturus choroid plexus (1988)
    Springer
    The journal of membrane biology 105 (1988), S. 207-219 
    Details
    ISSN: 1432-1424
    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
    URL: http://dx.doi.org/10.1007/BF01870998
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Ca2+-activated K+ currents inNecturus choroid plexus (1988)
    Springer
    The journal of membrane biology 105 (1988), S. 221-231 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01870999
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Digitale Medien
    Digitale Medien
    Evidence implicating protein kinase C in exocytosis from electropermeabilized bovine chromaffin cells (1988)
    Springer
    The journal of membrane biology 104 (1988), S. 21-34 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01871899
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    Defective regulation of apical membrane chloride transport and exocytosis in cystic fibrosis (1988)
    Springer
    Bioscience reports 8 (1988), S. 27-33 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF01128969
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Digitale Medien
    Digitale Medien
    Management of forest nursery soils dominated by calcium salts (1988)
    Springer
    New forests 2 (1988), S. 173-193 
    Details
    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
    URL: http://dx.doi.org/10.1007/BF00029987
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
    Digitale Medien
    Digitale Medien
    Properties of mitochondria from Penicillium cyclopium and their response to calcium and other divalent cations (1988)
    Springer
    Antonie van Leeuwenhoek 54 (1988), S. 221-228 
    Details
    ISSN: 1572-9699
    Schlagwort(e): calcium ; cation ; conidiation ; mitochondria ; respiration
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Biologie
    Notizen: Abstract The respiratory properties of isolated mitochondria from P. cyclopium were studied with particular attention to their response to calcium ions. The results obtained indicate concentration dependent stimulation of NADH oxidation by calcium ions. Similar effects could also be obtained with other divalent cations.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF00443580
    Standort Signatur Erwartet Verfügbarkeit
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