AHEART Mar. 45/3

Prakash, Y. S., A. A. Togaibayeva, M. S. Kannan, V. M. Miller, L. A. Fitzpatrick, and G. C. Sieck. Estrogen increases Ca21 efflux from female porcine coronary arterial smooth muscle. Am. J. Physiol. 276 (Heart Circ. Physiol. 45): H926–H934, 1999.—Acute estrogen administration relaxes vascular smooth muscle by decreasing intracellular Ca21 concentration ([Ca]i). In the present study, we examined the hypothesis that this reduction in [Ca]i is mediated in part by enhanced Ca21 efflux. Coronary artery smooth muscle cells were isolated from gonad-intact, sexually mature female pigs. The [Ca]i response to endothelin-1 was measured using fluo 3 and confocal microscopy. 17b-Estradiol (E2b), but not 17aestradiol or triamcinolone acetonide, caused a concentrationdependent (IC50 5 10 nM) decrease in the [Ca]i response to endothelin-1. This decrease was blocked by the specific estrogen receptor antagonist ICI-182780. Under conditions in which Ca21 influx and sarcoplasmic reticulum Ca21 reuptake were blocked, E2b still decreased [Ca]i. The response was blocked by extracellular lanthanum. These data indicate that E2b decreases [Ca]i in coronary artery smooth muscle by affecting Ca21 efflux via a receptor-mediated mechanism.