The role of differential activation of p38-mitogen-activated protein kinase in preconditioned ventricular myocytes

Activation of protein kinase C (PKC) and more recently mitogen-activated pr otein kinases (MAPKs) have been associated with the cardioprotective effect of ischemic preconditioning. We examined the interplay between these kinas es in a characterized model of ischemic preconditioning in cultured rat neo natal ventricular cardiocytes where ectopic expression of active PKC-delta results in protection. Two members of the MAPK family, p38 and p42/44, were activated transiently during preconditioning by brief simulated ischemia/r eoxygenation. Overexpression of active PKC-delta, rather than augmenting, c ompletely abolished this activation. We therefore determined whether a simi lar process occurred during lethal prolonged simulated ischemia. In contras t to ischemia, brief, lethal-simulated ischemia activated only p38 (2.8+/-0 .45 vs, basal, P<0.01), which was attenuated by expression of active PKC-<d elta> or by preconditioning (0.48+/-0.1 vs. ischemia, P<0.01). To determine whether reduced p38 activation was the cause or an effect of protection, w e used SB203580, a p38 inhibitor. SB203580 reduced ischemic injury (CK rele ase 38.0+/-3.1%, LDH release 77.3+/-4.0%, and MTT bioreduction 127.1+/-4.8% of control, n=20, P<0.05). To determine whether p38 activation was isoform selective, myocytes were infected with adenoviruses encoding wild-type p38 alpha or p38 beta. Transfected p38 alpha and beta show differential activa tion (P<0.001) during sustained simulated ischemia, with p38<alpha> remaini ng activated (1.48+/-0.36 vs, basal) but p38 beta deactivated (0.36+/-0.1 v s, basal, P<0.01). Prior preconditioning prevented the activation of p38<al pha> (0.65+/-0.11 vs. ischemia, P<0.05). Moreover, cells expressing a domin ant negative p38<alpha>, which prevented ischemic p38 activation, were resi stant to lethal. simulated ischemia (CK release 82.9+/-3.9% and MTT bioredu ction 130.2+/-6.5% of control, n=8, P<0.05). Thus, inhibition of p38<alpha> activation during ischemia reduces injury and may contribute to preconditi oning-induced cardioprotection in this model.