Genomic and nongenomic stimulatory effect of aldosterone on H+-ATPase in proximal S3 segments

Abstract

The genomic and nongenomic effects of aldosterone on the intracellular pH recovery rate (pHirr) via H+-ATPase and on cytosolic free calcium concentration ([Ca2+]i) were investigated in isolated proximal S3 segments of rats during superfusion with an Na+-free solution, by using the fluorescent probes BCECF-AM and FLUO-4-AM, respectively. The pHirr, after cellular acidification with a NH4Cl pulse, was 0.064 ± 0.003 pH units/min ( n = 17/74) and was abolished with concanamycin. Aldosterone (10−12, 10−10, 10−8, or 10−6M with 1-h or 15- or 2-min preincubation) increased the pHirr. The baseline [Ca2+]iwas 103 ± 2 nM ( n = 58). After 1 min of aldosterone preincubation, there was a transient and dose-dependent increase in [Ca2+]iand after 6-min preincubation there was a new increase in [Ca2+]ithat persisted after 1 h. Spironolactone [mineralocorticoid (MR) antagonist], actinomycin D, or cycloheximide did not affect the effects of aldosterone (15- or 2-min preincubation) on pHirr and on [Ca2+]ibut inhibited the effects of aldosterone (1-h preincubation) on these parameters. RU 486 [glucocorticoid (GR) antagonist] and dimethyl-BAPTA (Ca2+chelator) prevented the effect of aldosterone on both parameters. The data indicate a genomic (1 h, via MR) and a nongenomic action (15 or 2 min, probably via GR) on the H+-ATPase and on [Ca2+]i. The results are compatible with stimulation of the H+-ATPase by increases in [Ca2+]i(at 10−12-10−6M aldosterone) and inhibition of the H+-ATPase by decreases in [Ca2+]i(at 10−12or 10−6M aldosterone plus RU 486).