The action of ethacrynic acid on sodium efflux from single toad oocytes.

1. Ethacrynic acid (10(-3)M) at pH 7.4 caused approximately 83% inhibition of Na efflux from single dissected toad oocytes.2. Less inhibition was found at concentrations below 10(-3)M but higher concentrations did not cause greater inhibition.3. At an external pH of 7.0 the onset of inhibition was more rapid than at pH 7.4.4. Ouabain (10(-3)M) produced only 30% inhibition of the Na efflux, and the subsequent application of ethacrynic acid largely inhibited the remaining efflux.5. Application of ouabain, after ethacrynic acid had produced some 80% inhibition, caused only a further 9% drop in efflux.6. In uninhibited cells, Na efflux was found to be greater at pH 8.0, and less at pH 7.0 than at 7.4.