Estradiol induces the calcium-dependent translocation of endothelial nitric oxide synthase

Although estrogen is known to stimulate nitric oxide synthesis in vascular endothelium, the molecular mechanisms responsible for this effect remain to be elucidated. Using quantitative immunofluorescence imaging approaches, we have investigated the effect of estradiol on the subcellular targeting of endothelial nitric oxide synthase (eNOS) in bovine aortic endothelial cells. In unstimulated endothelial cells, eNOS is predominantly localized at the cell membrane. Within 5 min after the addition of estradiol, most of the eNOS translocates from the membrane to intracellular sites close to the nucleus. On more prolonged exposure to estradiol, most of the eNOS returns to the membrane. This effect of estradiol is evident at a concentration of 1 pM, and a maximal estradiol effect is seen at a concentration of 1 nM. Neither progesterone nor testosterone has any effect on eNOS distribution. After estradiol addition, a transient rise in intracellular Ca2+ concentration precedes eNOS translocation. Both the Ca2+-mobilizing and eNOS-translocating effects of estradiol are completely blocked by the estrogen receptor antagonist ICI 182,780, and the intracellular Ca2+ chelator 1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) prevents estradiol-induced eNOS translocation. Use of the nitric oxide-specific dye diaminofluorescein shows that estradiol treatment increases nitric oxide generation by endothelial cells; this response is blocked by ICI 182,780 and by the eNOS inhibitor Nomega-nitro-L-arginine. These results show that estradiol induces subcellular translocation of eNOS by a rapid, Ca2+-dependent, receptor-mediated mechanism, and they suggest a nongenomic role for estrogen in the modulation of NO-dependent vascular tone.