Effects of standard diuretics and ortho-vanadate on sodium transport across isolated frog skin.

Frog (Rana temporaria) skins were studied in an Ussing type lucite chamber adapted to diminish tissue edge damage. The transepithelial electrical potential difference, short circuit current and direct current (DC) resistance of skins mounted in this chamber were 56, 20 and 24% higher, respectively, than those of skins mounted in a conventional chamber. Amiloride, triamterene, ouabain and ortho-vanadate inhibited short circuit current and net mucosal to serosal flux of 22Na. Amiloride and triamterene had rapid onsets of action and were effective only when administered to the mucosal (pond) side of the skin. Ouabain and ortho-vanadate had slower onsets of action and were effective only when administered to the serosal side of the skin. Steady state of effects of these drugs was not reached within the three-hour period of the experiments. The inhibitory effect of ortho-vanadate was blocked by adding a disulfonic stilbene derivative (DIDS) to the serosal side of the skin. Serosal prostaglandin E2 stimulated the short-circuit current and decreased the DC resistance. Thiazides, acetazolamide and loop diuretics had no effects on Na+ transport by frog skin. Thus, frog skin seems to be a useful model only in studies of the mode of action and the structure-activity relationship of diuretic which act by inhibiting sodium entry or Na+-K+-ATPase activity.