Submitted on October 22, 2007
Accepted on April 21, 2008
Genomic deletion of estrogen receptors ER
and 
does not alter estrogen-mediated inhibition of Ca2+ influx and contraction in murine cardiomyocytes
Nina D Ullrich, Andree Krust, Peter Collins, and Kenneth T MacLeod1*
1 National Heart & Lung Institute, Imperial College, London, United Kingdom
* To whom correspondence should be addressed. E-mail: k.t.macleod{at}imperial.ac.uk.
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) 
and 
are involved. We measured the effect of estrogens on Ca2+ current (ICaL) in isolated ventricular cardiomyocytes of wild-type (WT), ER knock-out (KO) and ERKO mice using the whole-cell patch clamp technique at 37°C. No differences in current densities or inactivation profiles of ICaL were found under control conditions in WT, ERKO and ERKO cardiomyocytes suggesting that absence of either ER has no effect on functional properties of ICaL. In all groups, application of raloxifene (2µM), 17- or 17-estradiol (50µM) reduced ICaL (P<0.001). Raloxifene decreased ICaL by 44±9% (mean±SEM) in WT (n=5), 34±5% in ERKO (n=5) and 30±5% in ERKO (n=8). 17-estradiol reduced ICaL by 41±10% (WT, n=4), 34±12% (ERKO, n=7) and 38±8% (ERKO, n=7). 17-estradiol inhibited ICaL by 31±4% (WT, n=4), 28±6% (ERKO, n=3) and 42±3% (ERKO, 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 ER or .
