Sphingosine mediates the immediate negative inotropic effects of tumor necrosis factor-alpha in the adult mammalian cardiac myocyte

To determine whether activation of the neutral sphingomyelinase pathway was responsible for the immediate (<30 min) negative inotropic effects of tumor necro sis factor-alpha (TNF-alpha), we examined sphingosine levels in diluent and TNF-alpha-stimulated cardiac myocytes. TNF-alpha stimulation of adult feline cardiac myocytes provoked a rapid (<15 min) increase in the hydrolysis of [C-14]sphingomyelin in cell-free extracts, as well as an increase in ceramide mass, consistent with cytokine-induced activation of the neutral sphingomyelinase pathway, High performance liquid chromatographic analysis of lipid extracts from TNF-alpha-stimulated cardiac myocytes showed that TNF-alpha stimulation produced a rapid (<30 min) increase in free sphingosine levels, Moreover, exogenous D-sphingosine mimicked the effects of TNF-alpha on intracellular calcium homeostasis, as well as the negative inotropic effects of TNF-alpha in isolated contracting myocytes; time course studies showed that exogenous D-sphingosine produced abnormalities in cell shortening that were maximal at 5 min, Finally, blocking sphingosine production using an inhibitor of ceramidase, n-oleoylethanolamine, completely abrogated the negative inotropic effects of TNF-alpha in isolated contracting cardiac myocytes, Additional studies employing biologically active ceramide analogs and sphingosine l-phosphate suggested that neither the immediate precursor of sphingosine nor the immediate metabolite of sphingosine, respectively, were likely to be responsible for the immediate negative inotropic effects of TNF-alpha. Thus, these studies suggest that sphingosine mediates the immediate negative inotropic effects of TNF-alpha in isolated cardiac myocytes.