Mechanical Strain Suppresses Inducible Nitric-oxide Synthase in Cardiac Myocytes

Abstract We investigated the effects of precisely controlled mechanical strain on nitric-oxide synthase activity in cultured neonatal rat cardiac myocytes. Incubation of cardiac myocytes for 24 h with 4 ng/ml interleukin-1β and 100 units/ml interferon-γ stimulated an increase in nitric oxide production, inducible nitric-oxide synthase (iNOS) mRNA, and iNOS protein. Mechanical strain suppressed nitric oxide production, iNOS mRNA, and iNOS protein stimulated by cytokines in an amplitude-dependent manner. Losartan (1 μm), an angiotensin II type 1 receptor antagonist, weakly inhibited the effect of strain, suggesting that paracrine angiotensin II is not the mediator of the strain effect. In addition, cycloheximide (10 μm), a protein synthesis inhibitor, inhibited the effect of strain by 46%. Transforming growth factor-β (1 ng/ml) suppressed iNOS mRNA expression, but anti-transforming growth factor-β antibody (30 μg/ml) did not block the effect of strain. In contrast, staurosporine (100 nm; a nonselective protein kinase inhibitor), calphostin C (1 μm; a selective protein kinase C inhibitor), and pretreatment with phorbol 12-myristate 13-acetate abolished the effect of strain. Genistein (100 μm), a tyrosine kinase inhibitor, partially inhibited the effect of strain. Thus, cyclic mechanical deformation suppresses cytokine-induced iNOS expression in cardiac myocytes, and this effect is mediated at least partially via activation of protein kinase C.