Genomic and nongenomic dose-dependent biphasic effect of aldosterone on Na+/H+exchanger in proximal S3 segment: role of cytosolic calcium

Abstract

The effects of aldosterone on the intracellular pH recovery rate (pHirr) via Na+/H+exchanger and on the [Ca2+]iwere investigated in isolated rat S3 segment. Aldosterone [10−12, 10−10, or 10−8M with 1-h, 15- or 2-min preincubation (pi)] caused a dose-dependent increase in the pHirr, but aldosterone (10−6M with 1-h, 15- or 2-min pi) decreased it (these effects were prevented by HOE694 but not by S3226). After 1 min of aldosterone pi, there was a transient and dose-dependent increase of the [Ca2+]iand after 6-min pi there was a new increase of [Ca2+]ithat persisted after 1 h. Spironolactone, actinomycin D, or cycloheximide did not affect the effects of aldosterone (15- or 2-min pi) but inhibited the effects of aldosterone (1-h pi) on pHirr and on [Ca2+]i. RU 486 prevented the stimulatory effect of aldosterone (10−12M, 15- or 2-min pi) on both parameters and maintained the inhibitory effect of aldosterone (10−6M, 15- or 2-min pi) on the pHirr but reversed its stimulatory effect on the [Ca2+]ito an inhibitory effect. The data indicate a genomic (1 h, via MR) and a nongenomic action (15 or 2 min, probably via GR) on [Ca2+]iand on the basolateral NHE1 and are compatible with stimulation of the NHE1 by increases in [Ca2+]iin the lower range (at 10−12M aldosterone) and inhibition by increases at high levels (at 10−6M aldosterone) or decreases in [Ca2+]i(at 10−6M aldosterone plus RU 486).