Increased myocardial oxygen consumption by TNF-α is mediated by a sphingosine signaling pathway

The present study investigated the effect of tumor necrosis factor (TNF)-alpha on myocardial energy metabolism as estimated by myocardial oxygen consumption (M (V) over dot O-2). M (V) over dot O-2 of electrically stimulated isolated trabeculae of right ventricular Wistar rat myocardium was analyzed using a Clark-type oxygen probe. After the initial data collection in the absence of TNF-alpha, measurements were repeated after TNF-alpha stimulation. In separate experiments, pretreatment with the nitric oxide (NO) synthase inhibitor N-G-nitro-L-arginine methyl ester (L-NAME) or the ceramidase inhibitor n-oleoylethanolamine (NOE) was done to investigate NO/sphingosine- related effects. TNF-alpha impaired myocardial economy at increasing stimulation frequencies without altering baseline M (V) over dot O-2. Incubation with TNF-alpha in the presence of L-NAME further impaired myocardial economy. NOE preincubation abrogated the TNF-alpha effect on myocardial economy. Moreover, the negative inotropic effect of TNF-alpha was observed in NOE-pretreated but not L-NAME-pretreated muscle fibers. Exogenous sphingosine mimicked the TNF-alpha effect on mechanics and energetics. We conclude that TNF-alpha impairs the economy of chemomechanical energy transduction primarily through a sphingosine-mediated pathway.