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.