The excretion of hydrogen ion by the isolated amphibian skin: Effects of antidiuretic hormone and amiloride

Abstract

H + extrusion by the isolated skins of two amphibia, Rana ridibunda and Bufo bufo was studied in order to test for the presence of exchange mechanisms of the type Na +/H + and Cl −/HCO 3 −, which have been described in several epithelial structures. The preparations were mounted in chambers of the Ussing type, so that the short-circuit current could be used as a function of Na + transport and the pH-stat technique was utilized to determine the rates of H + extrusion under different experimental conditions. These conditions were either the withdrawal of the ions intervening in the mentioned exchanges (Cl - or Na +, or the addition of drugs with well-known effects on Na + uptake and transport (antidiuretic hormone and amiloride). In the frog skin, H + excretion was detected in solutions containing either Cl − or SO 4 2−, with identical rates. Again, Na + substitution by Mg 2+ had no effect on H + excretion rates, neither did the suppression of Na + influx by amiloride or its stimulation by antidiuretic hormone. These experiments were repeated with similar results in gland-free preparations of the epidermis of frog skin separated from the corion by the action of collagenase. Experiments in toad skin showed that H + excretion could not be detected when Cl − was present in the outer medium, but became apparent if an impermeant anion, SO 4 2−, was used. This observation is compatible with the existence of an exchange mechanism of the type Cl −/HCO 3 −. Secondly, in these preparations H + extrusion increased after stimulation with antidiuretic hormone and decreased when amiloride was used or when Na + was substituted by Mg 2+, suggesting that at least a fraction of the total H + efflux is linked to Na + influx. In the isolated frog skin this mechanism does not seem to be operative.