Role of lipid rafts in ceramide and nitric oxide signaling in the ischemic and preconditioned hearts

Nitric oxide plays a crucial role in myocardial ischemia reperfusion injury as well as in myocardial adaptation to ischemic stress. To understand the dichotomy of nitric oxide behavior in the ischemic myocardium, isolated rat hearts were subjected to ischemia/reperfusion protocol. The tissue contents of sphingomyelin (SM), ceramide and sphingosine were determined by high performance thin layer chromatography (HPTLC). The myocardial plasma proteins were immunoprecipitated with caveolin-1 specific antibody. Ischemia/reperfusion resulted in the breakdown of SM with corresponding accumulation of ceramide and sphingosine. Immunoprecipitation with eNOS-specific antibody revealed the association of eNOS with caveolin-1 fraction of the heart. Ischemia/reperfusion caused a depression of contractile function and an increased apoptotic cell death and myocardial infarct size, which were reversed by preperfusing the hearts with desipramine, an sphingomyelinase inhibitor that also prevented ceramide accumulation and eNOS association with caveolin-1. The similar results were obtained when the hearts were adapted to ischemic stress by subjecting them to repeated reversible ischemia and reperfusion. The results indicate that ischemia/reperfusion causes an increase in eNOS, which is unavailable to the ischemic heart because of its binding with caveolin-1. Ceramide plays a crucial role in this process, because prevention of ceramide formation either by myocardial adaptation to ischemia or with desipramine results in the inhibition of eNOS association with caveolin-1 thereby reducing myocardial ischemic reperfusion injury.