[Effect of N-ethylmaleimide on the active transport of sodium and its permeability in the skin of Rana esculenta].

N-ethyl maleimide (10(-3)M in the external fluid) strongly increases the permeability of urea and phenylalanine. However, the ratio phi 0 urea / phi 0 phenylalanine (a measure of membrane integrity) is not reduced. NEM 10(-4)M elicits a small increase of urea permeability. NEM (10(-3)M or 10(-4)M in the external fluid) stimulates Na active transport across the frog skin. Most probably the activation of Na pump is due to an increase of Na cellular pool, caused by the permeability increase elicited by NEM.