Estrogen increases Ca²⁺ efflux from female porcine coronary arterial smooth muscle

Acute estrogen administration relaxes vascular smooth muscle by decreasing intracellular Ca²⁺ concentration ([Ca²⁺](i)). In the present study, we examined the hypothesis that this reduction in [Ca²⁺](i) is mediated in part by enhanced Ca²⁺ efflux. Coronary artery smooth muscle cells were isolated from gonad-intact, sexually mature female pigs. The [Ca²⁺](i) response to endothelin-1 was measured using fluo 3 and confocal microscopy. 17β-Estradiol (E₂β), but not 17α-estradiol or triamcinolone acetonide, caused a concentration-dependent (IC₅₀ = 10 nM) decrease in the [Ca²⁺](i) response to endothelin-1. This decrease was blocked by the specific estrogen receptor antagonist ICI-182780. Under conditions in which Ca²⁺ influx and sarcoplasmic reticulum Ca²⁺ reuptake were blocked, E₂β still decreased [Ca²⁺](i). The response was blocked by extracellular lanthanum. These data indicate that E₂β decreases [Ca²⁺](i) in coronary artery smooth muscle by affecting Ca²⁺ efflux via a receptor-mediated mechanism.