ACUTE AND EARLY EFFECTS OF ALDOSTERONE ON NA-K-ATPASE ACTIVITY IN MADIN-DARBY CANINE KIDNEY EPITHELIAL-CELLS

The time course and mechanism of early effects of aldosterone on renal Na-K-adenosinetriphosphatase (Na-K-ATPase) activity and number of uni ts were studied in MDCK cells. Aldosterone induced a time- and dose-de pendent stimulation of Na-K-ATPase activity. The stimulatory effect of aldosterone on activity and number of pump units increased progressiv ely and was inhibited by spironolactone. In presence of cycloheximide, the stimulatory effect of aldosterone on activity and number of catal ytic sites persisted to the same extent until 30 min and decreased by 20% after 60 min. In these cells, dimethylamiloride addition during pr eincubation abolished the aldosterone-induced stimulation in Na-K-ATPa se activity up to 60 min. In contrast, furosemide addition did not alt er the effect of aldosterone on Na-K-ATPase activity. The present stud y demonstrates an early effect of aldosterone on Na-K-ATPase activity that can be separated into the following two successive periods: 1) in crease in pump number due to insertion of presynthetized units seconda ry to Na entry through an amiloride-sensitive apical pathway; and 2) a n increase in pump number by de novo protein synthesis.