EFFECTS OF AMINOPERIMIDINE ON ELECTROLYTE TRANSPORT ACROSS AMPHIBIAN SKIN

The effect of aminoperimidine (AP)on transepithelial Na+ transport and Cl- conductance (G(Cl)) of isolated amphibian skin (Bufo viridis and Rana esculenta) was analyzed using transepithelial and intracellular e lectrophysiological techniques. AP, applied at concentrations between 30 and 100 mu M from the mucosal side, stimulated Na+ transport rapidl y and reversibly by more than 30% of the control value due to an incre ase in apical membrane Na+ permeability. Influence of AP on basolatera l membrane conductance and effective driving force for Na+ were neglig ible. Voltage-activated G(Cl) of toad skin, but not the resting, deact ivated conductance, as well as spontaneously high G(Cl) in frog skin w as rapidly inhibited by AP in a concentration-dependent manner. The ha lf-maximal inhibitory concentration of 20 mu M is the highest hithero reported inhibitory power for G(Cl) in amphibian skin. The effect of A P on G(Cl) was slowly and incompletely reversible even after brief exp osure to the agent. Serosal application of AP had similar, albeit dela yed effects on both Nai and Cl- transport. AP did not interfere with t he Cl- pathway after it was opened by 100-300 mu M CPT-cAMP, a membran e-permeable, nonhydrolyzed analogue of cAMP. Inhibition of the voltage -activated G(Cl) by AP was attenuated or missing when AP was applied d uring voltage perturbation to serosa-positive potentials. Since AP is positively charged at physiological pH, it suggests that the affected site is located inside the Cl- pathway at a certain distance from the external surface. AP affects then the Na+ and Cl- transport pathways i ndependent of each other. The nature of chemical interference with AP, which is responsible for the influence on the transport of Na+ and Cl -, remains to be elucidated.