Estrogen stimulates NOS‐1 in coronary smooth muscle via PI3 kinase‐Akt signaling cascade

Sex steroids exert profound and controversial effects on cardiovascular function. For example, estrogens have been reported to either ameliorate or exacerbate coronary heart disease. Although estrogen dilates coronary arteries from a variety of species, the molecular basis for this acute, non‐genomic effect is unclear. Moreover, we know very little of how estrogen affects human coronary artery smooth muscle cells (HCASMC). We have combined molecular and cellular functional studies with protein analysis to now identify novel targets of estrogen action in HCASMC: Type 1 (neuronal) NOS and phosphatidyl inositol (PI) 3 kinase – Akt. Fluorescence studies demonstrated that 17beta‐estradiol (E2) increased NO production in HCASMC, and single‐channel patch‐clamp experiments revealed that stimulation of nNOS leads to increased activity of calcium‐activated potassium (BKCa) channels in these cells. Furthermore, over‐expression of nNOS protein in HCASMC greatly enhanced BKCa channel activity. Immunoblot studies demonstrated that E2 enhances Akt phorphorylation in HCASMC, and that 50nM wortmannin, a selective PI3 kinase inhibitor, attenuated E2‐stimulated channel activity, NO production, and Akt phosphorylation. These studies implicate the PI3 kinase/Akt signaling axis as an estrogen transduction component in HCASMC. We conclude, therefore, that estrogen opens BKCa channels in HCASMC by stimulating nNOS via a transduction sequence involving PI3 kinase and Akt. These findings now provide a molecular mechanism that can explain the clinical observation that estrogen enhances coronary blood flow in patients with diseased or damaged coronary arteries.