The effect of diuretics on Na+-K+-ATPase and c-AMP levels in toad bladder epithelial cells

Na+-K+-ATPase was inhibited by 1 times 10-4M ethacrynic acid and mercuderamide, and by 1 times 10-3M hydrochlorothiazide and furosemide. A modification of Gilman's (1970) protein displacement assay has been used to measure c-AMP levels in toad bladder epithelial cells. Vasopressin (50 mU/ml) caused c-AMP levels to rise from 4.27 to 9.27 pmol/mg protein. Ethacrynic acid had no effect on cellular c-AMP levels after 10 min exposure to the drug, but at 90 min caused a reduction of both basal and vasopressin stimulated levels. Furosemide caused an apparent rise in c-AMP levels, dilution ratio measurements indicated interference by this drug in the assay procedure, mecuderamide also caused substantial interference with the c-AMP assay. Hydrochlorothiazide had no effect on basal or hormone stimulated levels of c-AMP. It was concluded that the inhibition of sodium transport produced by ethacrynic acid in toad bladder is probably due to inhibition of adenylate cyclase, an effect not shared by other dieuretics.