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  • 1
    Electronic Resource
    Electronic Resource
    Na + transport and flux ratio through apical Na + channels in toad bladder (1982)
    [s.l.] : Nature Publishing Group
    Nature 297 (1982), S. 688-689 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Urinary bladders from toads (Bufo marinus) were mounted in Lucite chambers and short-circuited as described previously12. The serosal surface was bathed in KCl-sucrose medium to depolarize the basolateral membranes. In these conditions, the resistance and potential difference across the basolateral ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/297688a0
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  • 2
    Electronic Resource
    Electronic Resource
    CONTROL OF APICAL SODIUM PERMEABILITY IN THE TOAD URINARY BLADDER BY ALDOSTERONE (1981)
    Oxford, UK : Blackwell Publishing Ltd
    Annals of the New York Academy of Sciences 372 (1981), S. 0 
    Details
    ISSN: 1749-6632
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1749-6632.1981.tb15453.x
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  • 3
    Electronic Resource
    Electronic Resource
    Current-voltage analysis of apical sodium transport in toad urinary bladder: Effects of inhibitors of transport and metabolism (1980)
    Springer
    The journal of membrane biology 57 (1980), S. 59-71 
    Details
    ISSN: 1432-1424
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The basal-lateral surface of the epithelium of the urinary bladder of the toad (Bufo marinus) was depolarized by exposure of the serosal surface to 85mm KCL and 50mm sucrose. The extent of depolarization appeared to be virtually complete, as evaluated by the invariance in the transepithelial electrical potential difference and conductance on addition of nystatin (a monovalent cation ionophore) to the serosal medium. The Na-specific current (I Na) was defined as the current sensitive to the removal of Na from the mucosal medium or inhibitable by addition of amiloride to this medium. In the presence of the high K-sucrose serosal medium, rapid, serial, stepwise clamping of the transepithelial voltage (V) yielded a curvilinear dependence ofI Na onV; which is taken to represent theI–V curve of the apical Na channels. The constant field equation (Goldman, D.E. 1943;J. Gen. Physiol. 27:37) fits theI–V data points closely, allowing estimates to be made of the permeability to Na of the apical membrane (P Na) and of the intracellular Na activity (Na c ). Exposure of the apical surface to amiloride (5×10−7 m) decreasedP Na in proportion to the decrease inI Na (i.e., ∼70%) but decreased Na c only 25%. In contrast, an equivalent lent reduction inI Na elicited by exposure of the basallateral surface to ouabain was accompanied by only a 20% decrease inP Na and a sixfold increase in Na c . The effects of amiloride onP Na and ouabain on Na c are consistent with the primary pharmacological actions of these drugs. In addition,P Na appears to be under metabolic control, in that 2-deoxyglucose, a specific inhibitor of glycolysis, decreasedI Na andP Na proportionately, and lowered Na c marginally, effects indistinguishable from those obtained with amiloride.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868986
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  • 4
    Electronic Resource
    Electronic Resource
    The role of sodium-channel density in the natriferic response of the toad urinary bladder to an antidiuretic hormone (1982)
    Springer
    The journal of membrane biology 64 (1982), S. 77-89 
    Details
    ISSN: 1432-1424
    Keywords: transepithelial Na transport ; apical Na perme-ability ; Na-channel density ; oxytocin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Urinary bladders ofBufo marinus were depolarized, by raising the serosal K concentration, to facilitate voltage-clamping of the apical membrane. Passive Na transport across the apical membrane was then studied with near-instantaneous current-voltage curves obtained before and after eliciting a natriferic response with oxytocin. Fitting with the constant-field equation showed that the natriferic effect is accounted for by an increase in the apical Na permeability. It is accompanied by a small increase in cellular Na activity. Furthermore, fluctuation analysis of the amiloride-induced shot-noise component of the short-circuit current indicated that the permeability increase is not due to increased Na translocation through those Na channels which were already conducting prior to hormonal stimulation. Rather, the natriferic effects is found to be based on an increase in the population of transporting channels. It appears that, in response to the hormone, Na channels are rapidly “recruited” from a pool of electrically silent channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870770
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  • 5
    Electronic Resource
    Electronic Resource
    Ion selectivity of the apical membrane Na channel in the toad urinary bladder (1982)
    Springer
    The journal of membrane biology 67 (1982), S. 91-98 
    Details
    ISSN: 1432-1424
    Keywords: epithelial Na transport ; toad urinary bladder ; apical membrane ; ion selectivity ; Na channels
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The ion selectivity of the apical membrane Na channel in the toad urinary bladder was investigated. The electrical potential difference and resistance across the basal-lateral membrane were reduced using high concentrations of KCl in the serosal bathing medium, and gradients for various ions were imposed across the apical membrane by altering the composition of the mucosal bathing medium. Ion fluxes through the channel were measured as the transepithelial current inhibited by amiloride, a specific blocker of the channel's Na conductance. The selectivity sequence for alkali metal cations was H〉Li〉Na≫K. K, permeability was barely detectable; the selectivity for Na over K was about 1000:1. Ammonium, hydroxyl ammonium and hydrazinium ions were, like K, virtually impermeant. The results suggest that the size of the unhydrated ion is an important factor in determining permeability in this channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868651
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  • 6
    Electronic Resource
    Electronic Resource
    Single-channel recordings of apical membrane chloride conductance in A6 epithelial cells (1984)
    Springer
    The journal of membrane biology 80 (1984), S. 81-89 
    Details
    ISSN: 1432-1424
    Keywords: A6 cells ; chloride channels ; single-channel recording ; inactivation ; SITS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The apical membrane of epithelial cells from the A6 cell line grown on impermeable substrata was studied using the patch-clamp technique. We defined the apical membrane as that membrane in contact with the growth medium. In about 50% of the patches, channels with single-unit conductances of 360±45 pS in symmetrical 105mm NaCl solutions, and characteristic voltage-dependent inactivation were observed. Using excised membrane patches and varying the ionic composition of the bathing medium, we determined that the channels were anion selective, with a permeability ratio for Cl− over Na+ of about 9∶1, calculated from the reversal potential using the constantfield equation. The channel was most active at membrane potentials between ±20 mV and inactivated, usually within a few seconds, at higher potentials of either polarity. Reactivation from this inactivation was slow, sometimes requiring minutes. In addition to its fully open state, the channel could also enter a flickering state, which appeared to involve rapid transitions to one or more submaximal conductance levels. The channel was inhibited by the disulfonic stilbene SITS in a manner characteristic of reversible open-channel blockers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868692
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  • 7
    Electronic Resource
    Electronic Resource
    Voltage-dependent block by amiloride and other monovalent cations of apical Na channels in the toad urinary bladder (1984)
    Springer
    The journal of membrane biology 80 (1984), S. 153-165 
    Details
    ISSN: 1432-1424
    Keywords: toad urinary bladder ; epithelial Na channels ; amiloride ; voltage-dependent inhibition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Inhibition of the Na conductance of the apical membrane of the toad urinary bladder by amiloride, alkali cations and protons was voltage dependent. Bladders were bathed with a high K-sucrose serosal medium to reduce series basal-lateral resistance and potential difference. Transepithelial current-voltage relationships were measured over a voltage range of ±200 mV with a voltage ramp of frequency 0.5 to 1 Hz. Na channelI–V relationships were obtained by subtraction of currents measured in the presence of maximal doses of amiloride (10 to 20 μm). With submaximal doses of amiloride (0.05 to 0.5 μm), the degree of inhibition of the Na channel current (I Na) increased as the mucosal potential was made more positive. The data can be reasonably well explained by assuming that amiloride blocks Na transport by binding to a site which senses ∼12% of the transmembrane voltage difference.I Na was reduced in a qualitatively similar voltage-dependent manner by mucosal K, Rb, Cs and Tl (∼100mm) and by mucosal H (∼1mm). Block by these cations cannot be explained in terms of interactions with a single membrane-voltage-sensing site; a model in which there are two or more blocking sites in series provides a better description of the data. On the other hand, amiloride block was reduced competitively by mucosal Na and K, suggesting that occupation of the channel by one cation excludes occupancy by the others. ADH and ouabain also reduce the apparent affinity of amiloride for its blocking site. Thus, intracellular Na may also compete with amiloride for occupancy of the channel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01868771
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  • 8
    Electronic Resource
    Electronic Resource
    Aldosterone control of the density of sodium channels in the toad urinary bladder (1982)
    Springer
    The journal of membrane biology 64 (1982), S. 91-102 
    Details
    ISSN: 1432-1424
    Keywords: transepithelial Na transport ; apical Na permeability ; Na-channel density ; aldosterone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary Near-instantaneous current-voltage relationships and shot-noise analysis of amiloride-induced current fluctuations were used to estimate apical membrane permeability to Na (P Na), intraepithelial Na activity (Na c ), single-channel Na currents (i) and the number of open (conducting) apical Na channels (N0), in the urinary bladder of the toad (Bufo marinus). To facilitate voltageclamping of the apical membrane, the serosal plasma membranes were depolarized by substitution of a high KCl (85mm) sucrose (50mm) medium for the conventional Na-Ringer's solution on the serosal side. Aldosterone (5×10−7 m, serosal side only) elicited proportionate increases in the Na-specific current (I Na and inP Na, with no significant change in the dependence ofP Na on mucosal Na (Na o ).P Na and the control ofP Na by aldosterone were substrate-dependent: In substrate-depleted bladders, pretreatment with aldosterone markedly augmented the response to pyruvate (7.5×10−3 m) which evoked coordinate and equivalent increases inI Na andP Na. The aldosterone-dependent increase inP Na was a result of an equivalent increase in the area density of conducting apical Na channels. The computed single-channel current did not change. We propose that, following aldosterone-induced protein synthesis, there is a reversible metabolically-dependent recruitment of preexisting Na channels from a reservoir of electrically undetectable channels. The results do not exclude the possibility of a complementary induction of Na-channel synthesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870771
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