Abstract
Estrogens modify contraction of vascular smooth muscle and cardiomyocytes, but suggestions that they confer protective effects on the cardiovascular system remain controversial. The negative inotropic effects of estrogens are a consequence of L-type Ca2+ channel inhibition, but the underlying mechanisms remain elusive. We tested the hypothesis that membrane-associated estrogen receptors (ER)-alpha and -beta are involved. We measured the effect of estrogens on Ca2+ current (ICaL) in isolated ventricular cardiomyocytes of wild-type (WT), ERalpha knockout (ERalphaKO), and ERbetaKO mice using the whole cell patch-clamp technique at 37 degrees C. No differences in current densities or inactivation profiles of ICaL were found under control conditions in WT, ERalphaKO, and ERbetaKO cardiomyocytes, suggesting that absence of either ER has no effect on functional properties of ICaL. In all groups, application of raloxifene (2 microM) or 17alpha- or 17beta-estradiol (50 microM) reduced ICaL (P < 0.001). Raloxifene decreased ICaL by 44 +/- 9% (mean +/- SE) in WT (n = 5), 34 +/- 5% in ERalphaKO (n = 5), and 30 +/- 5% in ERbetaKO mice (n = 8). 17alpha-Estradiol reduced ICaL by 41 +/- 10% in WT (n = 4), 34 +/- 12% in ERalphaKO (n = 7), and 38 +/- 8% in ERbetaKO mice (n = 7). 17beta-Estradiol inhibited ICaL by 31 +/- 4% in WT (n = 4), 28 +/- 6% in ERalphaKO (n = 3), and 42 +/- 3% in ERbetaKO mice (n = 5). Decreases in cell shortening occurred in parallel with these findings. Our results suggest that inhibition of ICaL and the decrease in contraction by estrogens do not depend on ERalpha or ERbeta.