Porcine ventricular endocardial cells in culture express the inducible form of nitric oxide synthase.

1. We have investigated whether porcine endocardial cells in culture express the inducible, Ca(2+)-independent form of nitric oxide (NO) synthase. 2. NO synthase activity in cytosolic extracts of endocardial cells was measured by estimation of the rate of formation of L-[14C]-citrulline from L-[14C]-arginine. 3. Treatment of the cells in culture with lipopolysaccharide or cytokines induced a Ca(2+)-independent NO synthase activity in the cell cytosol. The combination of tumour necrosis factor (TNF alpha, 10 ng ml-1) and interleukin-1 beta (IL-1 beta, 10 ng ml-1) induced the greatest enzyme activity. 4. The increased Ca(2+)-independent NO synthase activity following exposure to cytokines was paralleled by an increase in guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels in the endocardial cell cytosol. 5. Simultaneous addition of dexamethasone (0.01-1 microM) or cycloheximide (0.03-3 microM) inhibited in a concentration-dependent manner TNF alpha- and IL-1 beta-induced expression of Ca(2+)-independent NO synthase activity. Neither dexamethasone (1 microM) nor cycloheximide (3 microM) had any effect on the activity of the constitutive NO synthase. 6. The possible pathophysiological consequences of endocardial expression of the inducible NO synthase are discussed.