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Acid secretion through the Rana esculenta skin: involvement of an anion‐exchange mechanism at the basolateral membrane.

Kinetic and electrophysiological studies were carried out to characterize the efflux of HCO3‐ (or OH‐) across the basolateral membrane of the proton‐secreting cells of the frog skin epithelium bathed with dilute saline mucosal solutions. In control conditions, the acidification of the mucosal solution (JnH+) was correlated directly with serosal alkalinization. Cl‐ substitution in the serosal Ringer (by gluconate or methylsulphate ions) induced an inhibition of proton excretion (70% inhibition). Measurements of the basolateral membrane potential with conventional micro‐electrodes and of cell Cl‐ activity (aCli) and proton activity with double‐barrelled ion‐sensitive micro‐electrodes recorded a basolateral membrane depolarization of 5.1 +/‐ 0.7 mV (n = 12), a decrease in aCli from 14.5 +/‐ 1.6 mequiv l‐1 to 1.8 +/‐ 0.3 mequiv l‐1 (n = 12), and a cell pH increase from 7.18 +/‐ 0.04 to 7.32 +/‐ 0.06 (n = 12) after serosal Cl‐ replacement. 4,4'‐diisothiocyanostilbene‐2‐2'‐disulphonic acid (DIDS) (10(‐4) M) and meclofenamate (5 X 10(‐5) M) inhibit JHn+ by 34% and 53% respectively whereas bumetanide did not block JHn+. Depolarization of the basolateral membrane (2 mM‐Ba2+ addition to the serosal solution) did not block proton excretion. We show that cell Cl‐ activity is maintained at a higher level than that predicted by the equilibrium potential, by a mechanism located at the basolateral membrane of the epithelium since the apical solution was Cl(‐)‐free. This mechanism is not sensitive to potential changes at the basolateral membrane in the range tested. An electroneutral Cl(‐)‐HCO3‐ exchange mechanism is the simplest hypothesis which can account for our results.