Na+-K+-ATPase inhibitors and renin release: relationship to calcium.

The inhibition of renin secretion and the vasoconstrictive action of cardiac glycosides may be attributed to increases in cytosolic calcium as a result of inhibition of Na+-K+-ATPase. These studies examined in the dog in vivo the role of calcium on the renal actions of ouabain as assessed from the modifying effects of calcium channel blockers. Since vanadate, another Na+-K+-ATPase, inhibitor, enhances in vitro the binding of ouabain to Na+-K+-ATPase, we examined the capacity of vanadate to modify the renal effects of ouabain in vivo. Infusion of ouabain (1 microgram X kg-1 X min-1) into the renal artery decreased RBF, GFR, and renin secretion, and produced diuresis and natriuresis. When ouabain was infused in dogs receiving the calcium channel blocker verapamil (100 microgram/min), it failed to suppress renin secretion or cause renal vasoconstriction. In addition, verapamil produced diuresis and natriuresis, which were greatly enhanced by ouabain (e.g., verapamil FENa 12.0 +/- 1.1----34.2 +/- 5.1%). The data strongly suggest that calcium entry into cells is a major mediator of the renin inhibitory effect and of the renal vasoconstriction induced by cardiac glycosides. The natriuresis observed during the calcium channel blocker infusion suggests that this drug may have a direct tubular effect on sodium reabsorption. Superimposition of vanadate (0.5 mumol/min) on ouabain infusion led to massive natriuresis (FENa, 5 +/- 1----35 +/- 4%), renal vasodilation (RBF 90 +/- 12----170 +/- 15 ml/min), and an increase in renin secretion (delta, 100%).(ABSTRACT TRUNCATED AT 250 WORDS)