CALCIUM-CHANNEL BLOCKADE ENHANCES NITRIC-OXIDE SYNTHASE EXPRESSION BYCULTURED ENDOTHELIAL-CELLS

In a recent study, we found marked increases in nitric oxide (NO) prod uction and endothelial and inducible NO synthase (eNOS and iNOS) expre ssions with calcium channel blockade in rats with chronic renal failur e. This study was undertaken to determine whether enhanced NO producti on with calcium channel blockade is a direct effect of this therapy or a consequence of the associated hemodynamic and humoral changes. We t ested 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 ma sses in proliferating and quiescent rat aortic endothelial cells in cu lture. 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 mod ify the stimulatory action of 10% fetal calf serum on DNA synthesis (t hymidine incorporation) and cell proliferation. Ca2+-independent NOS a ctivity and iNOS protein expression were negligible and unaffected by calcium channel blockade. NOx production and NOS expression were great er in proliferating cells than in quiescent cells. Thus, calcium chann el blockade upregulates endothelial NO production in vitro, confirming our previous in vivo study. This observation indicates that the reduc tions in cytosolic [Ca2+] and vasodilation with calcium channel blocka de are not only due to inhibition of Ca2+ entry but also to an NO-cCMP -mediated mechanism.