title: 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-/HCO3-, 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 techinique was utilize to determine the rates of H+ extrusion under different experimental conditions. The conditions were either the withdrawal of the ions intervening the mentioned exchanges (Cl- or Na+), or the addition of drugs with well-known effects on Na+ up-take and transport (antidiuretic hormone and amiloride). In the frog skin, H+ excretion was detected in solutions containing either Cl- or SO4-2-, 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 that H+ excretion could not be detected whan Cl- was present in the outer medium, but became apparent if an impermant anion, SO4-2-, was used. This observation is compatible with the existence of an exchange mechanism of the type Cl-/HCO3-. 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+, suggesting that a 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.
mesh_terms: D000584:Amiloride / Q000494:pharmacology*; D000818:Animals; D001693:Biological Transport, Active; D002023:Bufo bufo; D002712:Chlorides / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D008274:Magnesium / Q000494:pharmacology; D011719:Pyrazines / Q000494:pharmacology*; D011898:Ranidae; D012867:Skin / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism / Q000494:pharmacology; D013045:Species Specificity; D013431:Sulfates / Q000494:pharmacology; D013997:Time Factors; D014667:Vasopressins / Q000494:pharmacology*
chemical_list: D002712:Chlorides; D011719:Pyrazines; D013431:Sulfates; D014667:Vasopressins; D000584:Amiloride; D012964:Sodium; D008274:Magnesium