AJP - Cell Physiology, Vol 261, Issue 4 C650-C657, Copyright © 1991 by American Physiological Society
Effect of mucosal halides on Ca(2+)-blockable currents through the skin of Rana ridibunda
F. Lacaz-Vieira and W. Van Driessche
Departamento de Fisiologia e Biofisica, Universidade de Sao Paulo, Brazil.
The present study deals with the interaction of mucosal anions with apical
Ca(2+)-blockable cation channels of the skin of Rana ridibunda. The
intracellular potential was depolarized by exposing the basolateral
membranes to K2SO4 Ringer solution. The apical bathing medium consisted of
nominal Ca(2+)-free K+ or Na+ solutions with SO4(2-), Cl-, Br-, or I- as
the major anion. The effects of mucosal anion substitutions were studied by
analyzing 1) the fluctuation in K+ current across the apical membrane
driven by imposed transepithelial clamping potentials and 2) alterations of
the transepithelial current (It) and conductance (Gt) as well as the
Lorentzian parameters in response to anion substitution in the mucosal
bathing solution. It and current noise spectra were recorded at different
transepithelial potentials (Vt). A Lorentzian component was present in the
power density spectrum when Vt was clamped at mucosa-positive voltages.
Such noise components were never observed with mucosa-negative potentials.
These findings suggest a rectifying behavior of the transepithelial cation
currents. The Lorentzian noise component and the inward-oriented cation
currents were depressed by the addition of micromolar concentrations of
Ca2+ to the apical solutions as well as by replacing mucosal K+ or Na+ by
N-methyl-D-glucamine. The Ca(2+)-blockable current and Lorentzian noise
plateau (So) were gradually increased by raising Vt. Both parameters, as
well as the corner frequency (fc), depended strongly on the major anion
species in the apical solution; replacing mucosal SO4(2-) by one of the
halides tested reduced fc and elevated So, It, and Gt considerably.
