Chronotropic effects of cytokines and the nitric oxide synthase inhibitor, L-NMMA, on cardiac myocytes.

We and others have proposed that cytokine-stimulated nitric oxide (NO) production is responsible for reversible myocardial depression in sepsis, trauma and ischemia. An effect of NO on cardiac sarcolemmal L-type calcium channels has also recently been proposed. The spontaneous beating rate of neonatal cardiac myocytes is regulated by the sarcolemmal L-type calcium channel. Accordingly, we sought to determine if cytokine-stimulated NO production could also regulate beating rates of neonatal cardiac myocytes. Treatment of neonatal rat cardiac myocytes with TNF, IL-1, IL-6, 10(-5)M NMA, or 10(-3)M NMA significantly enhanced spontaneous beating rates compared to untreated myocytes in serum-free media for 48 hours (p < or = .01; n = 12 for each). Only IL-1 treatment resulted in significant nitrite levels vs. control over 48 hours (4.2 +/- 0.7 vs. 0.3 +/- 0.2 nmoles/1.25 x 10(-5) cells, respectively) (n = 12). Nitrite production by IL-1 was inhibited by 10(-3)M NMA but not 10(-5)M NMA (0.3 +/- 0.2 vs. 4.1 +/- 0.6 nmoles; p < .01; n = 12). The addition of 10(-5)M NMA to TNF, IL-1, and IL-6 did not alter the effect of the cytokines on the spontaneous beating rates of the cardiac cells (p < or = .01; n = 12 for each). These results strongly suggest that cytokines and NMA affect cardiac myocyte spontaneous beating rates through mechanisms independent of NO.