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Basolateral membrane potential and conductance in frog skin exposed to high serosal potassium

The Journal of Membrane Biology, ISSN: 0022-2631, Vol: 90, Issue: 1, Page: 89-96
1986
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In studies of apical membrane current-voltage relationships, in order to avoid laborious intracellular microelectrode techniques, tight epithelia are commonly exposed to high serosal K concentrations. This approach depends on the assumptions that high serosal K reduces the basolateral membrane resistance and potential to insignificantly low levels, so that transepithelial values can be attributed to the apical membrane. We have here examined the validity of these assumptions in frog skins (Rana pipiens pipiens). The skins were equilibrated in NaCl Ringer's solutions, with transepithelial voltage V clamped (except for brief perturbations ΔV) at zero. The skins were impaled from the outer surface with 1.5 m KCl-filled microelectrodes (R>30 MΩ). The transepithelial (short-circuit) current l and conductance g=-ΔI/ΔV, the outer membrane voltage V (apical reference) and voltage-divider ratio (F=ΔV/ΔV), and the microelectrode resistance R were recorded continuously. Intermittent brief apical exposure to 20 μm amiloride permitted estimation of cellular (c) and paracellular (p) currents and conductances. The basolateral (inner) membrane conductance was estimated by two independent means: either from values of g and F before and after amiloride or as the ratio of changes (-ΔI/ΔV) induced by amiloride. On serosal substitution of Na by K, within about 10 min, I declined and g increased markedly, mainly as a consequence of increase in g. The basolateral membrane voltage (V(=-V) was depolarized from 75±4 to 2±1 mV [mean±sem (n=6)], and was partially repolarized following amiloride to 5±2 mV. The basolateral conductance increased in high serosal K, as estimated by both methods. Essentially complete depolarization of the basolateral membrane and increase in its conductance in response to high [K] were obtained also when the main serosal anion was SO or NO instead of Cl. On clamping V over the range 0 to +125 mV in KSO-depolarized skins, the quasi-steady-state VV relationship was linear, with a mean slope of 0.88±0.03. The above results demonstrate that, in a variety of conditions, exposure to high serosal K results in essentially complete depolarization of the basolateral membrane and a large increase in its conductance. © 1986 Springer-Verlag New York Inc.

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