Prevention of Ischemic Preconditioning Only by Combined Inhibition of Protein Kinase C and Protein Tyrosine Kinase in Pigs

In rabbits, inhibition of either protein kinase C or protein tyrosine kinase abolishes the infarct size reduction achieved by ischemic preconditioning. In pigs, however, inhibition of protein kinase C does not attenuate ischemic preconditioning. The present study tested whether inhibition of protein tyrosine kinase alone or in combination with inhibition of protein kinase C interferes with ischemic preconditioning in pigs. In 29 enflurane-anesthetized pigs, the LAD was cannulated and perfused from an extracorporeal circuit. Protein tyrosine kinase and protein kinase C were inhibited by continuous intracoronary infusion of genistein (5×10−6mol/l) and staurosporine (10−7mol/l), respectively. Subendocardial blood flow (ENDO) was measured with microspheres. Infarct size was analysed by TTC staining (% of LV area at risk) following 90 min low-flow ischemia and 120 min reperfusion. In the presence of genistein, 90 min ischemia at an ENDO of 0.06±0.01 (± ) ml/min/g resulted in an infarct size of 16.7±4.2% (n=8). With genistein, ischemic preconditioning by 10 min ischemia and 15 min reperfusion still reduced infarct size to 6.5±2.7% (ENDO: 0.05±0.01 ml/min/g,n=7,P<0.05). In the presence of both genistein and staurosporine, infarct size following 90 min ischemia was 14.1±3.6% (ENDO: 0.06±0.01 ml/min/g,n=7). With genistein and staurosporine, ischemic preconditioning no longer reduced infarct size significantly (11.5±3.1%, ENDO: 0.06±0.01 ml/min/g,n=7). The effective attenuation of ischemic preconditioning only by simultaneous inhibition of both, protein kinase C and protein tyrosine kinase, suggests a complex signal cascade involving both protein kinases.