In vitro inhibition of rat kidney plasma membrane Na-K-ATPase activity by triamterene

In vitro experiments were performed to study the effect of 2,4,7-triamino-6-phenylpteridine (triamterene), a potassium sparing diuretic agent, upon the rat kidney plasma membrane Na-K-ATPase activity. Triamterene in the concentration range from 8X10(-13) mol/l to 8X10(-3) mol/l exerted a dose-dependent inhibitory effect of the rat kidney plasma membrane Na-K-Mg-ATPase and Na-K-ATPase activities--estimated IC50 values lay at about 8X10(-3) mol/l and 8X10(-7) mol/l, respectively. The diuretic did not influence the activity of Mg-ATPase, except at very high concentration. A Lineweaver-Burk analysis demonstrated that the inhibition of Na-K-ATPase by triamterene was non-competitive. The in vitro inhibitory effect, together with an in vivo effect observed before points to a possibility that the natriuresis caused by triamterene is due, at least partly, to a direct inhibition of active sodium transport across the kidney plasma membrane.