PKC mediates LPS- and phorbol-induced cardiac cell nitric oxide synthase activity and hypocontractility

Lipopolysaccharide (LPS) treatment impairs cardiac myocyte contractility in a nitric oxide synthase (NOS)-dependent manner. The objective of this study was to assess whether protein kinase C (PKC) transduces the LPS signal into an enhanced NOS activity in rat cardiac myocytes. LPS (100 ng/ml) stimulated myocyte PKC activity, inducible NOS (iNOS) expression, and NOS activity in a time- and protein synthesis-dependent fashion. Directly activating PKC with beta-phorbol 12,13-dibutyrate (beta-PDB) also induced myocyte iNOS synthesis and NOS activity and reduced electrically stimulated contractility, while the inactive alpha-PDB was ineffectual. Contractility could be restored to beta-PDB-incubated cells by superfusion with the NOS inhibitor N omega-nitro-L-arginine methyl ester. PKC blockade with sphingosine, chelerythrine, or calphostin-C precluded LPS- and beta-PDB-induced increases in NOS activity and protected contractility. Depletion of PKC by 18 h of incubation with beta-PDB in the presence of chelerythrine also blocked acquisition of enhanced NOS activity and contractile dysfunction when the myocytes were subsequently exposed to LPS. These findings suggest that PKC is a significant intracellular mediator for the effects of LPS on cardiac cell NOS activity and contractile function.