Differential effects of progesterone and 17β-estradiol on the Ca²⁺ entry induced by thapsigargin and endothelin-1 in in situ endothelial cells

The effects of progesterone and 17β-estradiol on Ca²⁺ signaling in in situ endothelial cells were investigated using front-surface fluorometry of fura-2-loaded strips of porcine aortic valve. Progesterone inhibited the thapsigargin-induced sustained [Ca²⁺](i) elevation (IC₅₀ = 33.9 μM, n = 4), while 17β-estradiol added a transient [Ca²⁺](i) elevation. Progesterone and 17β-estradiol had no significant effect on the thapsigargin-induced [Ca²⁺](i) elevations in the absence of extracellular Ca²⁺. A Mn²⁺-induced decline of fluorescent intensity at 360 nm excitation was accelerated by thapsigargin. This acceleration was completely reversed by progesterone, but not by 17β-estradiol. Progesterone inhibited, and 17β-estradiol enhanced the endothelin-1 (ET-1)-induced [Ca²⁺](i) elevation, while both had no effect on the ET-1-induced Ca²⁺ release observed in the absence of extracellular Ca²⁺ or in the pertussis toxin-treated strips. Progesterone and 17β-estradiol thus had different effects on Ca²⁺ signaling, especially on Ca²⁺ influx, in endothelial cells. (C) 2000 Elsevier Science B.V.