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 necrosis 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 [14C]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 1-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.
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Cardiology Section, Department of Medicine, Veterans Administration Medical Center, Baylor College of Medicine, Houston, Texas 77030, USA.
Dorn
G W
GW
Mann
D L
DL
D000818:Animals; D002415:Cats; D002478:Cells, Cultured; D009200:Myocardial Contraction; D009206:Myocardium / Q000378:metabolism*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D013110:Sphingosine / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D014409:Tumor Necrosis Factor-alpha; D013108:Sphingomyelin Phosphodiesterase; D013110:Sphingosine