Effect of estrogen on calcium and sodium transport by the nephron luminal membranes

Estrogens are widely used for contraception and osteoporosis prevention. The aim of the present study was to investigate the effect of 17 beta -estradiol on calcium (Ca2+) transport by the nephron luminal membranes, independently of any other Ca2+-regulating hormones. Proximal and distal tubules of rabbit kidneys were incubated with 17 beta -estradiol or the carrier for various periods of time. and the luminal membranes of these tubules were purified and vesiculated. Ca2+ uptake by membrane vesicles was measured using the Millipore filtration technique. Incubation of proximal tubules with the hormone did not influence Ca2+ uptake by the luminal membranes, In contrast, incubation of distal tubules with 10(-8) M 17 beta -estradiol for 30 min decreased the initial uptake of 0.5 mM Ca2+ from 0.34 +/- 0.04 (S.E.M.) to 0.17 +/- 0.04 pmol/mug per 5 s (P <0.05). In the presence of 100 mM Na+, 0-5 mM Ca2+, uptake was strongly diminished and the effect of 17 beta -estradiol disappeared (0.17 +/- 0.01 and 0.21 +/- 0.07 pmol/mug per 5 s in vesicles from the control and treated tubules). Direct incubation of the membranes with 17p-estradiol, however, failed to show any influence of the hormone on Ca2+ transport. The action of 17 beta -estradiol was dose-dependent, with a half-maximal effect at approximately 10(-9) M. Ca2+ uptake by the distal tubule membranes presents dual kinetics. 17 beta -Estradiol decreased the V-max value of the high-affinity component from 0.42 +/- 0.02 to 0.31 +/- 0.03 pmol/mug per 10 s (P <0.02). In contrast with the effect of the hormone on Ca2+ transport, estradiol increased Na+ uptake by both the proximal and distal tubule luminal membranes. In conclusion, incubation of proximal and distal tubules with estrogen decreases Ca2+ reabsorption by the high-affinity Ca2+ channels of the distal luminal membranes, and enhances Na+ transport by the membranes from proximal and distal nephrons.