Effect of 17 β-estradiol on the intracellular calcium concentration and eNOS protein expression in human endothelial cells
Many reports indicate nitric oxide (NO) production plays an important role in mediating the effects of estrogen on the vasculature. Here, we report the modulatory effects of 17 ?-estradiol (E2) on intracellular calcium concentration ([Ca2+]i), a cofactor in the activity of endothelial NO synthase (eNOS), and eNOS expression in human endothelial cells (EA.hy926). [Ca2+]i in Fura 2 loaded cells was measured using spectrofluorometry. In the presence of extracellular Ca2+, inhibition of the endoplasmic reticulum (ER) Ca2+-ATPase with thapsigargin (TG) caused a bi-phasic increase in [Ca2+]i in the cells. However, the extent of TG-induced initial [Ca2+]i increase was significantly higher in E2 treated cells than its control counterpart. A subsequent increase in extracellular Ca2+ concentration led to a robust increase in [Ca2+]i, which was completely blocked by the non-specific calcium channel blocker Ni2+. Elevation of [Ca2+]i in response to added calcium was significantly higher in E2 treated cells relative to controls. Removal of extracellular Ca2+ changed the [Ca2+]i signal to a single [Ca2+]i transient, indicating that Ca2+ release from ER contributes to the initial [Ca2+]i peak, while the maintained plateau is due to Ca2+ entry. Using Western blotting, we demonstrated that eNOS expression in E2 treated cells was significantly higher than in controls. This action of E2 was abrogated by estrogen receptor antagonist ICI 182,780. These results suggest E2-regulated Ca2+ homeostasis may play a role in the enhancement of eNOS in endothelial cells (Supported by NHLBI).
Effect of 17 β-estradiol on the intracellular calcium concentration and eNOS protein expression in human endothelial cells.
FASEB Journal, 20(4),