A monthly cycle during third trimester pregnancy in the serum concentrations of progesterone and aldosterone and the urinary excretion rate of potassium

Estrogen acutely inhibits ion transport by isolated stria vascularis

We investigated the nongenomic effects of female sex steroid hormones on the short circuit current (I(sc,probe)) across gerbil stria vascularis using the voltage-sensitive vibrating probe. The strial marginal cell epithelial layer produces I(sc,probe) by secreting K+ via I(Ks) channels in the apical membrane. Application of 17beta-estradiol (E2) caused a decrease of I(sc,probe) in a dose-dependent manner (10 nM-10 microM) within seconds. Tamoxifen, a competitive inhibitor of the intracellular estrogen receptor, did not change the inhibitory effect of E2. Activation of I(Ks) channels by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid in the presence and absence of E2 was used to test the mechanism of action. The results were consistent with a direct inhibitory effect of E2 on the I(Ks) channels. By contrast, progesterone caused a transient increase of I(sc,probe). These results suggest that E2 decreases secretion of K+ by inhibition of I(Ks) channels via a nongenomic mechanism at concentrations near those occurring under some physiologic conditions while progesterone caused only transient effects on I(sc,probe).

Inhibition of minK protein induced K+ channels in Xenopus oocytes by estrogens

Previously it was shown that minK protein expression in uterus is regulated by estrogen. In the present study, we were interested in putative direct effects of estrogen on minK protein induced K+ currents (IminK) in Xenopus oocytes. Superfusion with 17-beta-estradiol (1 microM) resulted in an inhibition of minK-induced currents, but had no appreciable effects on the delayed rectifier and inward rectifier K+ channels Kv1.1 and Kir2.1, respectively. The inhibition of IminK by 17-beta-estradiol was concentration-dependent, with an IC50 of approximately 0.5 microM. In the presence of 17-beta-estradiol, the conductance-voltage relationship was shifted to more depolarized potentials. IminK inhibition occurred also in the presence of the estrogen-receptor antagonist tamoxifen, suggesting that a mechanism independent of estrogen receptors is involved. The synthetic estrogen diethylstilbestrol (DES) also inhibited IminK but with a lower affinity (IC50 of 4.5 microM), while cortisol and progesterone had only weak effects on IminK. In summary, the results indicate that estrogens directly inhibit IminK.

Electrophysiological effects of progesterone on hepatocytes

The addition of progesterone (1-100 mumol/l) to the extracellular fluid bathing rat hepatocytes led to a rapid and fully reversible depolarization of the cell membrane. The progesterone-induced depolarization was paralleled by a decrease of potassium selectivity and an increase of cell membrane resistance and was abolished in the presence of the potassium channel blocker barium. Accordingly, in whole cell recordings, progesterone led to a decrease of the cell membrane conductance. 17 alpha-Hydroxyprogesterone and beta-estradiol were less effective by a factor of 10, whereas cholesterol, corticosterone and hydrocortisone did not significantly alter the potential difference across the cell membrane. In conclusion, acute administration of progesterone depolarized rat hepatocytes by decreasing the potassium conductance of the cell membrane.

Progesterone inhibits K conductance in plasma membrane of cultured renal epitheloid MDCK cells

Progesterone causes natriuresis, an effect largely attributed to displacement of aldosterone from its receptor. The present study, however, demonstrates that progesterone (0.1, 1, and 10 mumol/1, respectively) also causes a rapid, fully reversible depolarization of Madin-Darby canine kidney (MDCK) cells (by 1.3 +/- 0.5, 4.1 +/- 0.7 and 12.3 +/- 1.5 mV, respectively). 17 alpha-Hydroxyprogesterone and dihydroxytestosterone are, by two orders of magnitude, less effective, whereas cholesterol, aldosterone, hydrocortisone, and estradiol (each up to 10 mumol/l) did not significantly alter the potential difference across the cell membrane. The effect of progesterone is blunted by antiprogestogen RU 486 (5 mumol/l). The progesterone-induced depolarization is paralleled by a decrease of potassium selectivity and an increase of cell membrane resistance and is abolished in the presence of the potassium channel blocker barium (10 mmol/l), as well as in the presence of 40 mmol/l potassium in the extracellular fluid. Neither removal of extracellular chloride or bicarbonate nor amiloride, ouabain, or pretreatment with pertussis toxin abolish the depolarizing effect of 5 mumol/l progesterone. In conclusion, acute administration of progesterone depolarizes MDCK cells by decreasing the potassium conductance of the cell membrane.