In vitro exposure of cultured cardiac and non-cardiac cells to aldosterone (aldo) in high concentrations has been reported to upregulate the Na+-K+ pump. We examined the effect of in vivo aldosterone on the Na+-K+ pump. Rabbits received aldo for 7 days via osmotic minipumps to induce a modest increase in plasma aldosterone levels. Na+-K+ pump current (Ip) was measured in isolated ventricular myocytes. Mean Ip of myocytes from aldotreated rabbits was significantly (P<0.001) lower than mean Ip of myocytes from vehicle-control rabbits when the Na+ concentration in pipette solutions was near-physiological intracellular levels (10 mM). In contrast, aldo treatment did not alter pump activity when near-saturating levels of Na+ (80 mM) were used. To examine if the aldosterone-induced decrease in Ip was mediated by the classical mineralocorticoid receptor rabbits were treated with both aldo and spironolactone. Spironolactone treatment completely eliminated the aldosterone-induced pump inhibition. We conclude that the effect of modest elevations of aldosterone levels in vivo on the cardiac sarcolemmal Na+-K+ pump is the opposite of reported in vitro effects.
|Publication status||Published - 20 Mar 1998|