Impairment of Na+ transport across frog skin by Tl+: Effects on turnover, area density and saturation kinetics of apical Na+ channels

1986 ◽  
Vol 407 (2) ◽  
pp. 145-152 ◽  
Author(s):  
W. Zeiske ◽  
W. Van Driessche
Keyword(s):  
Frog Skin ◽  
Na Channels ◽  
Na Transport ◽  
Area Density ◽  
Saturation Kinetics ◽  
Kinetics Of

scholarly journals Blocker-related changes of channel density. Analysis of a three-state model for apical Na channels of frog skin.

1990 ◽  
Vol 95 (4) ◽  
pp. 647-678 ◽  
Author(s):  
S I Helman ◽  
L M Baxendale
Keyword(s):  
Frog Skin ◽  
Noise Analysis ◽  
Kinetic Scheme ◽  
State Model ◽  
Na Channel ◽  
Na Channels ◽  
Na Transport ◽  
Open Probability ◽  
Wide Range ◽  
Three State Model

Blocker-induced noise analysis of apical membrane Na channels of epithelia of frog skin was carried out with the electroneutral blocker (CDPC, 6-chloro-3,5-diamino-pyrazine-2-carboxamide) that permitted determination of the changes of single-channel Na currents and channel densities with minimal inhibition of the macroscopic rates of Na transport (Baxendale, L. M., and S. I. Helman. 1986. Biophys. J. 49:160a). Experiments were designed to resolve changes of channel densities due to mass law action (and hence the kinetic scheme of blocker interaction with the Na channel) and to autoregulation of Na channel densities that occur as a consequence of inhibition of Na transport. Mass law action changes of channel densities conformed to a kinetic scheme of closed, open, and blocked states where blocker interacts predominantly if not solely with open channels. Such behavior was best observed in "pulse" protocol experiments that minimized the time of exposure to blocker and thus minimized the contribution of much longer time constant autoregulatory influences on channel densities. Analysis of data derived from pulse, staircase, and other experimental protocols using both CDPC and amiloride as noise-inducing blockers and interpreted within the context of a three-state model revealed that Na channel open probability in the absence of blocker averaged near 0.5 with a wide range among tissues between 0.1 and 0.9.

Basis for apparent saturation kinetics of Na+ influx in freshwater hyperregulators

1988 ◽  
Vol 254 (6) ◽  
pp. R984-R988
Author(s):  
L. B. Kirschner
Keyword(s):  
Transport System ◽  
Open Circuit ◽  
Na Transport ◽  
Proton Efflux ◽  
Electrical Neutrality ◽  
Saturation Kinetics ◽  
Kinetics Of ◽  
Stimulation Of ◽  
Cl Permeability

Uptake of Na+ by intact frogs has been reported to show saturation kinetics at low external concentrations (less than 2 mM); yet other evidence shows that the transport system is far from saturated in this concentration range. The saturation behavior was reproduced here in isolated frog skins that were then used as appropriate models for investigating the paradox. When the skin was bathed by 2 mM Na+ outside and open circuited, influx (JNain) was near maximum. If, under these conditions, the skin was short circuited, JNain increased threefold. Alternatively, if Cl- permeability was increased in the open-circuited skin, JNain doubled. Both perturbations uncouple JNain from the efflux of a cation (nominally H+), which normally maintains electrical neutrality under open-circuit conditions. This suggests that the apparent saturation of JNain is caused by limiting efflux of the counterion. In confirmation of this prediction, stimulation of proton efflux markedly increased JNain. Thus the apparent Michaelis-Menten kinetics observed in frogs, and probably in other freshwater animals as well, do not represent saturation of an element in Na+ transport, either the amiloride-sensitive apical channel or the basolateral Na+-K+-ATPase.

Dependence of intracellular Na+ concentration on apical and basolateral membrane Na+ influx in frog skin

1985 ◽  
Vol 249 (5) ◽  
pp. F662-F671
Author(s):  
J. S. Stoddard ◽  
S. I. Helman
Keyword(s):  
Epithelial Cells ◽  
Frog Skin ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Na Transport ◽  
Maximal Inhibition ◽  
Basolateral Membranes ◽  
Isotopic Method ◽  
Rate Of Increase ◽  
Kinetics Of

An isotopic method was developed to measure the intracellular Na+ content of the transepithelial Na+ transport pool of frog skin. Isolated epithelia (no corium) were labeled with 24Na either asymmetrically, from apical (Aa) or basolateral (Ab) solutions, or symmetrically (Aab). Transport pool Na+ could be identified from the kinetics of washout of 24Na carried out in the presence of 1 mM ouabain, 100 microM amiloride, and 1 mM furosemide that served to trap cold Na+ and 24Na within the transport pool. In control epithelia, Aab averaged 64.1 neq/cm2 (13.9 mM), and maximal inhibition of apical membrane Na+ entry with 100 microM amiloride caused Aab to decrease to 24.3 neq/cm2 (5.3 mM). Ouabain caused Aab to increase markedly to 303 neq/cm2 in 30 min, whereas amiloride inhibition of apical membrane Na+ entry reduced markedly the rate of increase of Aab caused by ouabain (7.3 neq X cm-2 X min-1 in control and 1.7 neq X cm-2 X min-1 in the presence of amiloride). These data, in part, confirmed the existence of an important basolateral membrane permeability to Na+ that was measured in separate studies of the bidirectional 24Na fluxes at the basolateral membranes of the cells. Both sets of data were supportive of the idea that a significant Na+ recycling exists at the basolateral membranes of the cells that contributes to the Na+ load on the pump and Na+ recycling participates in the regulation of the Na+ concentration of the Na+ transport pool of these epithelial cells.

Saturation kinetics of sodium efflux across isolated frog skin

1976 ◽  
Vol 231 (4) ◽  
pp. 995-1001 ◽  
Author(s):  
TU Biber ◽  
TL Mullen
Keyword(s):  
Active Transport ◽  
Frog Skin ◽  
Apical Cell ◽  
Transport Pathway ◽  
Sodium Efflux ◽  
Saturation Kinetics ◽  
Transcellular Pathway ◽  
Na Efflux ◽  
Edge Damage ◽  
Kinetics Of

Measurement of Na efflux across the frog skin epithelium from the serosal side to the outside (JNa 3 leads to 1) in a new chamber specifically designed to avoid edge damage shows that JNa 3 leads to 1 exhibits saturation kinetics with a maximal efflux (Jmax) of 31.8 nmol/cm2 per h and an apparent KNa of 4.0 mM. In contrast, JNa 3 leads to 1 measured in conventional chambers and efflux determinations in the new chamber of substances that pass the epithelium via extracellular pathways (polyethylene glycol 900, sucrose, mannitol) exhibit a linear relationship between the efflux of the substance in question and its concentration in the bath. In addition, changes in external Na concentration do not cause substantial changes in JNa 3 leads to 1. The saturation remains but both Jmax and KNa increase after application of ouabain. Amiloride, as well as dinitrophenol, eliminates the saturation and JNa 3 leads to 1 becomes a linear function of Na concentration. The separate effects of ouabain and amiloride suggest that these two inhibitors which are known to affect two distinctly different steps in the active transport pathway act also on two separate steps of JNa 3 leads to 1: the passage across the inward- (serosal) and outward-facing (apical) cell membranes of the epithelial cells, respectively. The action of dinitrophenol indicates the involvement of metabolism in JNa 3 leads to 1 probably at the latter of the two steps. The results suggest strongly that JNa 3 leads to 1 proceeds not via a paracellular but via a transcellular pathway that interacts with the active transport pathway.

Effects of ouabain and furosemide on basolateral membrane Na efflux of frog skin

1983 ◽  
Vol 245 (3) ◽  
pp. F312-F321
Author(s):  
T. C. Cox ◽  
S. I. Helman
Keyword(s):  
Frog Skin ◽  
Basolateral Membrane ◽  
Ringer Solution ◽  
Na Transport ◽  
Consistent Effect ◽  
Unstirred Layers ◽  
Substantial Inhibition ◽  
Na Efflux ◽  
Kinetics Of ◽  
Single Exponential

The kinetics of Na tracer fluxes were reinvestigated in isolated epithelia of frog skin in which the unstirred layers of the corium were removed. The rate of appearance of 22Na in the basolateral solution (JNa13) conformed to a single exponential for tracer buildup with a mean t1/2 of 1.9 min. The Na transport pool labeled isotopically from the apical solution was about 40 neq/cm2 for epithelia bathed in either a chloride or sulfate Ringer solution. Basolateral-to-apical solution unidirectional Na flux (JNa31) was low, averaging 0.7 microA/cm2 and remained low for 40 min of ouabain treatment of the epithelia. In agreement with electrophysiological data, ouabain at 10(-4) M caused an acute inhibition (less than 1 min) of the Na efflux at the basolateral membrane (JNa23), falling to 40.6 and 26.7% of control for epithelia bathed in Cl and SO4 Ringer, respectively. Although furosemide exerted little or no consistent effect on the Na flux of control epithelia, this drug in ouabain-poisoned epithelia caused a substantial inhibition of a neutral, chloride-dependent, ouabain-insensitive Na efflux. It is suggested that ouabain "induces" a neutral mechanism of Na transport at the basolateral membrane of the cells that is chloride dependent and furosemide sensitive.

The Sigma-1 Receptor Ligands Chlorpromazine and Trifluoperazine Inhibit Na+ Transport in Frog Skin Epithelium

BIOPHYSICS ◽  
2020 ◽  
Vol 65 (5) ◽  
pp. 784-787
Author(s):  
A. V. Melnitskaya ◽  
Z. I. Krutetskaya ◽  
V. G. Antonov ◽  
N. I. Krutetskaya
Keyword(s):  
Frog Skin ◽  
Receptor Ligands ◽  
Na Transport ◽  
Sigma 1 Receptor ◽  
Skin Epithelium ◽  
Frog Skin Epithelium ◽  
Sigma 1

pHi determines rate of sodium transport in frog skin: results of a new method to determine pHi

1994 ◽  
Vol 266 (3) ◽  
pp. F367-F374 ◽  
Author(s):  
R. Rick
Keyword(s):  
Frog Skin ◽  
Nuclear Potential ◽  
Na Channel ◽  
Cytoplasmic Ph ◽  
Na Transport ◽  
Principal Cells ◽  
Weak Organic Acid ◽  
Transepithelial Na Transport ◽  
Cell Layers ◽  
Important Regulator

The pH of the isolated frog skin epithelium was determined on a cellular and subcellular level based on the distribution of a weak organic acid, 4-bromobenzoic acid. The indicator is detectable by X-ray microanalysis due to the presence of an element label. The results show that the pH of principal cells, but not the Na concentration, is closely correlated with the rate of transepithelial Na transport. Acidification leads to an inhibition of Na transport, regardless of whether the change was spontaneous or experimentally induced. Under the conditions of this study, the pH of principal cells was not well regulated. At a bath pH of 7.0, large pH differences between the cell layers were detectable. In mitochondria-rich cells, the pH was a function of the intracellular Cl concentration but not the Na transport rate. The cytoplasmic pH consistently exceeded the nuclear pH. The nuclear-cytoplasmic pH differential in principal cells amounted to 0.3 pH units, which is equivalent to a nuclear potential of -17 mV. The results support the view that the intracellular pH (pHi) is an important regulator of transepithelial Na transport. Regulation is primarily achieved at the level of the apical Na channel, making the Na influx the rate-limiting step in Na reabsorption.

Mechanisms and sequelae of increased alveolar fluid clearance in hyperoxic rats

1997 ◽  
Vol 272 (3) ◽  
pp. L407-L412 ◽  
Author(s):  
G. Yue ◽  
S. Matalon
Keyword(s):  
Alveolar Epithelial Cells ◽  
Na Channels ◽  
Alveolar Fluid Clearance ◽  
Na Transport ◽  
Alveolar Epithelial ◽  
Lung Fluid ◽  
Isotonic Fluid ◽  
Epithelial Na Channels ◽  
Alveolar Edema

We instilled 4 ml isotonic fluid containing trace amounts of fluorescently labeled dextran (molecular mass 150 kDa) in the lungs of rats exposed to either 85% O(2) for 7 days or to 85% O(2) for 7 days and 100% O(2) for 3 days. We withdrew the fluid every hour for a 3-h period and calculated alveolar fluid clearance (AFC) from changes in dextran concentration. Postinstillation (3 h), AFC values in the control and the two hyperoxic groups were 51 +/- 1, 63 +/- 2, and 62 +/- 3 (SE), respectively (%instilled volume; n > or = 5; P < 0.05). Addition of either 1 mM amiloride or N-ethyl-N-isopropyl amiloride (EIPA) in the instillate decreased the AFC values in all groups 3 h later to approximately 30% of instilled volume. Instillation of phenamil, an irreversible blocker of epithelial Na+ channels into the lungs of rats exposed to 85% O(2) for 7 days and 100% O(2) for 2 days, resulted in a significant increase of their extravascular lung fluid volumes 24 h later. These results demonstrate the existence of EIPA-inhibitable Na+ channels in alveolar epithelial cells in vivo and indicate that an increase in Na+ transport plays an important role in limiting the amount of alveolar edema in O(2)-damaged lungs.

Coupling of volume and Na+ transport in frog skin epithelium

1989 ◽  
Vol 66 (1-2) ◽  
pp. 183-190 ◽  
Author(s):  
Cherng-Shing R. Tang ◽  
Kim Peterson-Yantorno ◽  
Mortimer M. Civan
Keyword(s):  
Frog Skin ◽  
Na Transport ◽  
Skin Epithelium ◽  
Frog Skin Epithelium
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