Abstract
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 17β-estradiol (E 2) caused a decrease of I sc,probe in a dose-dependent manner (10 nM–10 μM) within seconds. Tamoxifen, a competitive inhibitor of the intracellular estrogen receptor, did not change the inhibitory effect of E 2. Activation of I Ks channels by 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid in the presence and absence of E 2 was used to test the mechanism of action. The results were consistent with a direct inhibitory effect of E 2 on the I Ks channels. By contrast, progesterone caused a transient increase of I sc,probe. These results suggest that E 2 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.
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