[Effect of N-ethylmaleimide, introduced in to the serous fluid, on the active transport of sodium through the skin of Rana esculenta].

An SH reactive agent, N-ethylmaleimide (NEM), if introduced in the serosal bath (10(-4) M), stimulates the short circuit current (SCC) across the frog skin. This effect is due to an increase of Na active transport, because is inhibited by ouabain (10(-4) M). A stimulatory action on Cl- or HCO3- secretion can be ruled out because the rise in SCC occurs also in the absence of Cl- or HCO3-. It is known that NEM inhibits the ADH action by forming covalent bounds with SH groups of ADH membrane receptors (1). Thus it is possible that this binding should mimic the ADH action on SCC. In order to test this hypothesis, we studied the effect of serosal NEM on SCC both in the absence and in the presence of I midazol (20 mM), an activator of the cyclic AMP phosphodiesterase. Imidazol treatment decreases the effect of NEM on SCC. Thus we conclude that NEM serosal treatment is able to mimic some ADH effects, by using the same ways of the ormone action.