Genomic deletion of estrogen receptors ERα and ERβ does not alter estrogen-mediated inhibition of Ca2+influx and contraction in murine cardiomyocytes

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)-α and -β are involved. We measured the effect of estrogens on Ca²⁺current ( I_CaL) in isolated ventricular cardiomyocytes of wild-type (WT), ERα knockout (ERαKO), and ERβKO mice using the whole cell patch-clamp technique at 37°C. No differences in current densities or inactivation profiles of I_CaLwere found under control conditions in WT, ERαKO, and ERβKO cardiomyocytes, suggesting that absence of either ER has no effect on functional properties of I_CaL. In all groups, application of raloxifene (2 μM) or 17α- or 17β-estradiol (50 μM) reduced I_CaL( P < 0.001). Raloxifene decreased I_CaLby 44 ± 9% (mean ± SE) in WT ( n = 5), 34 ± 5% in ERαKO ( n = 5), and 30 ± 5% in ERβKO mice ( n = 8). 17α-Estradiol reduced I_CaLby 41 ± 10% in WT ( n = 4), 34 ± 12% in ERαKO ( n = 7), and 38 ± 8% in ERβKO mice ( n = 7). 17β-Estradiol inhibited I_CaLby 31 ± 4% in WT ( n = 4), 28 ± 6% in ERαKO ( n = 3), and 42 ± 3% in ERβKO mice ( n = 5). Decreases in cell shortening occurred in parallel with these findings. Our results suggest that inhibition of I_CaLand the decrease in contraction by estrogens do not depend on ERα or ERβ.