Influence of extracellular Cl concentration on Cl transport across isolated skin ofRana Pipiens

Biber, Thomas U. L.; Walker, Thomas C.; Mullen, Terry L.

doi:10.1007/bf01869355

Cited by 19 publications

(3 citation statements)

References 25 publications

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“…In some experiments, on the other hand, it was observed that in obviously "good" impalements the amilorideinduced level of fR o did not exceed 0.92. This could result from conductance of the apical plasma membrane to ions other than sodium, e.g., potassium or chloride [2]. To what extent lateral intercellular space resistance affects the accuracy of our estimates of fRo is presently unknown.…”

Section: Methodsmentioning

confidence: 99%

Relationship of transepithelial electrical potential to membrane potentials and conductance ratios in frog skin

Nagel

Essig

1982

J. Membrain Biol.

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Previous studies in anuran epithelia have shown that, after clamping the transepithelial voltage in symmetrical sequences for 4-6 min there is near-constancy of the rate of active Na transport and the associated oxidative metabolism, with a near-linear potential dependence of both. Here we have investigated in frog skin the cellular electrophysiolgical events associated with voltage clamping (Vt = inside-outside potential). Increase and decrease of Vt produced converse effects, related directly to the magnitude of Vt. Hyperpolarization resulted in prompt decrease in inward transepithelial current It and increase in fractional outer membrane resistance fRo (as evaluated from small transient voltage perturbations) and in outer membrane potential Vo. Overshoot of Vo was followed by relaxation to a quasi-steady state in minutes. Changes in fRo were progressive, with half times of some 1-5 sec. Changes in transepithelial slope conductance gt were more variable, usually preventing precise evaluation of the outer and inner cell membrane conductances go and gi. Nevertheless, it was shown that go is related inversely to Vt and Vo. Presuming insensitivity of gi to Vt, the dependence of Go on Vo in the steady state much exceeds that predicted by the constant field equation. Apparent inconsistencies with earlier results of others may be attributable to differences in protocol and the complex dependence of go on Vo and/or cellular-current. In contrast to previous findings in tight epithelia at open circuit, differences in Vt were associated with substantial differences in fRo and inner membrane potential Vi. Hyperpolarization of Vt over ranges commonly employed in studies of active transport ad metabolism appears to increase significantly the electrochemical work per Na ion transported.

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Section: Methodsmentioning

confidence: 99%

Relationship of transepithelial electrical potential to membrane potentials and conductance ratios in frog skin

Nagel

Essig

1982

J. Membrain Biol.

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“…15 , where the apical H + -pumps and Cl − /HCO 3 − exchangers in series with basolateral Cl − channels carry one negative charge across the cell for every Cl − moved from the outside to the inside solution. We ( Dürr and Larsen, 1985 ) and others ( Biber et al, 1980 ), however, have also published studies where the active Cl − flux did not generate a transepithelial current. It appears, therefore, that under some conditions a majority of MR-cells expressing Cl − /HCO 3 − exchangers in the apical membrane does not express proton pumps in this membrane but, rather, in the basolateral membrane.…”

Section: Discussionmentioning

confidence: 88%

Proton Pump Activity of Mitochondria-rich Cells

Jensen

Sørensen

Larsen

et al. 1997

The Journal of General Physiology

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We have hypothesized that a major role of the apical H+-pump in mitochondria-rich (MR) cells of amphibian skin is to energize active uptake of Cl− via an apical Cl−/HCO3 −-exchanger. The activity of the H+ pump was studied by monitoring mucosal [H+]-profiles with a pH-sensitive microelectrode. With gluconate as mucosal anion, pH adjacent to the cornified cell layer was 0.98 ± 0.07 (mean ± SEM) pH-units below that of the lightly buffered bulk solution (pH = 7.40). The average distance at which the pH-gradient is dissipated was 382 ± 18 μm, corresponding to an estimated “unstirred layer” thickness of 329 ± 29 μm. Mucosal acidification was dependent on serosal pCO2, and abolished after depression of cellular energy metabolism, confirming that mucosal acidification results from active transport of H+. The [H+] was practically similar adjacent to all cells and independent of whether the microelectrode tip was positioned near an MR-cell or a principal cell. To evaluate [H+]-profiles created by a multitude of MR-cells, a mathematical model is proposed which assumes that the H+ distribution is governed by steady diffusion from a number of point sources defining a set of particular solutions to Laplace's equation. Model calculations predicted that with a physiological density of MR cells, the [H+] profile would be governed by so many sources that their individual contributions could not be experimentally resolved. The flux equation was integrated to provide a general mathematical expression for an external standing [H+]–gradient in the unstirred layer. This case was treated as free diffusion of protons and proton-loaded buffer molecules carrying away the protons extruded by the pump into the unstirred layer; the expression derived was used for estimating stationary proton-fluxes. The external [H+]-gradient depended on the mucosal anion such as to indicate that base (HCO3 −) is excreted in exchange not only for Cl −, but also for Br− and I−, indicating that the active fluxes of these anions can be attributed to mitochondria-rich cells.

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“…Several studies suggest activation of the skin C1-conductance by external CI ions (Kirschner, 1970;Mandel & Curran, 1972;Alvarado, Dietz & Mullen, 1975;Bruus et al, 1976;Rodriguez-Boulan et al, 1978;Kristensen, 1978;Biber, Walker & Mullen, 1980;Ehrenfeld & Garcia-Romeu, 1980;Kirschner, 1983;Katz & Larsen, 1984;Harck & Larsen, 1985).…”

Section: Introductionmentioning

confidence: 99%

Roles of external and cellular Cl− ions on the activation of an apical electrodiffusional Cl− pathway in toad skin

Procópio

Lacaz-Vieira

1990

J. Membrain Biol.

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This study is concerned with the short-circuit current, Isc, responses of the Cl(-)-transporting cells of toad skin submitted to sudden changes of the external Cl- concentration, [Cl]o. Sudden changes of [Cl]o, carried out under apical membrane depolarization, allowed comparison of the roles of [Cl]o and [Cl]cell on the activation of the apical Cl- pathways. Equilibration of short-circuited skins symmetrically in K-Ringer's solutions of different Cl- concentrations permitted adjustment of [Cl]cell to different levels. For a given Cl- concentration (in the range of 11.7 to 117 mM) on both sides of a depolarized apical membrane, this structure exhibits a high Cl- permeability, P(Cl)apical. On the other hand, for the same range of [Cl]cell but with [Cl]o = 0, P(Cl)apical is reduced to negligible values. These observations indicate that when the apical membrane is depolarized P(Cl)apical is modulated by [Cl]o; in the absence of external Cl- ions, intracellular Cl- is not sufficient to activate P(Cl)apical. Computer simulation shows that the fast Cl- currents induced across the apical membrane by sudden shifts of [Cl]o from a control equilibrium value strictly follow the laws of electrodiffusion. For each experimental group, the computer-generated Isc versus [( Cl]cell - [Cl]o) curve which best fits the experimental data can only be obtained by a unique pair of P(Cl)apical and Rb (resistance of the basolateral membrane), thus allowing the calculation of these parameters. The electrodiffusional behavior of the net Cl- flux across the apical membrane supports the channel nature of the apical Cl- pathways in the Cl(-)-transporting cells. Cl- ions contribute significantly to the overall conductance of the basolateral membrane even in the presence of a high K concentration in the internal solution.

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Influence of extracellular Cl concentration on Cl transport across isolated skin ofRana Pipiens

Cited by 19 publications

References 25 publications

Relationship of transepithelial electrical potential to membrane potentials and conductance ratios in frog skin

Relationship of transepithelial electrical potential to membrane potentials and conductance ratios in frog skin

Proton Pump Activity of Mitochondria-rich Cells

Roles of external and cellular Cl− ions on the activation of an apical electrodiffusional Cl− pathway in toad skin

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