Calcium channel blockade enhances nitric oxide synthase expression by cultured endothelial cells

In a recent study, we found marked increases in nitric oxide (NO) production and endothelial and inducible NO synthase (eNOS and iNOS) expressions with calcium channel blockade in rats with chronic renal failure. This study was undertaken to determine whether enhanced NO production with calcium channel blockade is a direct effect of this therapy or a consequence of the associated hemodynamic and humoral changes. We tested the effects of a calcium channel blocker, felodipine (10(-5), 10(-6), and 10(-7) mol/L), on nitrate and nitrite (NOx) generation, Ca2+-dependent and -independent NOS activity, and eNOS and iNOS protein masses in proliferating and quiescent rat aortic endothelial cells in culture. Compared with vehicle alone, felodipine significantly increased NOx generation, Ca2+-dependent NOS activity, and eNOS protein mass in proliferating and quiescent endothelial cells. Felodipine did not modify the stimulatory action of 10% fetal calf serum on DNA synthesis (thymidine incorporation) and cell proliferation. Ca2+-independent NOS activity and iNOS protein expression were negligible and unaffected by calcium channel blockade. NOx production and NOS expression were greater in proliferating cells than in quiescent cells. Thus, calcium channel blockade upregulates endothelial NO production in vitro, confirming our previous in vivo study. This observation indicates that the reductions in cytosolic [Ca2+] and vasodilation with calcium channel blockade are not only due to inhibition of Ca2+ entry but also to an NO-cCMP-mediated mechanism.