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Calcium channel blockade enhances nitric oxide synthase expression by cultured endothelial cells
1Division of Nephrology, Department of Medicine, University of California at Irvine, Irvine, CA, USA.
Abstract:
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-cGMP mediated mechanism.
Insights
Calcium channel blockers like felodipine directly increase nitric oxide (NO) production in endothelial cells. This enhanced NO generation contributes to vasodilation, independent of hemodynamic changes.
Area of Science:
- Cardiovascular Pharmacology
- Endothelial Biology
- Renal Physiology
Background:
- Calcium channel blockade (CCB) in chronic renal failure (CRF) is associated with increased nitric oxide (NO) and NO synthase (NOS) expression.
- The direct effect of CCB on NO production versus indirect hemodynamic effects remains unclear.
Purpose of the Study:
- To investigate if CCB directly enhances NO production in endothelial cells.
- To determine the impact of CCB on NO generation, NOS activity, and NOS protein expression in vitro.
Main Methods:
- Cultured rat aortic endothelial cells (proliferating and quiescent) were treated with felodipine (a CCB) at varying concentrations.
- Nitrate and nitrite (NOx) generation, Ca2+-dependent and -independent NOS activity, and eNOS and iNOS protein masses were measured.
Main Results:
- Felodipine significantly increased NOx generation, Ca2+-dependent NOS activity, and eNOS protein mass in both cell types.
- No significant changes were observed in Ca2+-independent NOS activity or iNOS expression.
- NOx production and NOS expression were higher in proliferating cells compared to quiescent cells.
Conclusions:
- Calcium channel blockade directly upregulates endothelial nitric oxide production in vitro.
- This effect is mediated by increased eNOS activity and expression, contributing to vasodilation via an NO-cGMP pathway.