EFFECTS OF DIPHENYLHYDANTOIN ON ACTIVE SODIUM TRANSPORT IN FROG SKIN

¹ Department of Pharmacology, University of Utah College of Medicine, Salt Lake City, Utah

Sodium transport in frog skin, measured by means of the short-circuit current and by means of radioactive sodium measurements, was stimulated by the addition of various doses of diphenylhydantoin (DPH) to the outside bathing solution. An effect of DPH on permeability sites at the outer cell membrane of frog skin was distinguished from a direct effect on the sodium pump by the following determinations: analysis of the relationship between short-circuit current and epithelial exchangeable sodium and a comparison of DPH with vasopressin, an agent shown to increase active sodium transport by increasing the permeability of the outer cell membrane to sodium ions. Analysis of the short-circuit current-epithelial exchangeable sodium relationship revealed that DPH, like vasopressin, increased membrane permeability to sodium ions. DPH was effective in stimulating active sodium transport in the presence of maximal effect of vasopressin and vasopressin was effective in the presence of a maximal effect of DPH. These results indicate that DPH and vasopressin do not compete with each other but act independently at different sites which appear to be located at the same barrier to sodium movement in the skin.