PHOSPHORYLATION OF TYROSINE-182 OF P38 MITOGEN-ACTIVATED PROTEIN-KINASE CORRELATES WITH THE PROTECTION OF PRECONDITIONING IN THE RABBIT HEART

p38 mitogen-activated protein kinase (MAPK) is known to be activated a fter exposure to endotoxin, osmotic and environmental stress, and, mos t recently, during ischemia/reperfusion. We investigated whether ische mic preconditioning also causes phosphorylation of the activation site s on p38 MAPK. Three groups of isolated rabbit hearts were studied, Co ntrol hearts experienced 30 min of ischemia only. The second group was preconditioned with 5 min of global ischemia and 10 min of reperfusio n. Group 3 was also ischemically preconditioned, but in the presence o f 100 mu M 8-(p-sulfophenyl)theophylline (SPT), Transmural left ventri cular biopsies were taken before and during the long ischemic period. Western blot analysis with either p38 MAPK or phospho-specific p38 MAP K (Tyr-182) antibodies showed a decreased phosphorylation during ische mia in non-preconditioned hearts, but phosphorylation was enhanced sev eral fold after 10 and 20 mill of ischemia in preconditioned hearts, F urthermore, when protection from ischemic preconditioning was blocked by SPT, increased phosphorylation of p38 MAPK during ischemia was not present, Therefore the phosphorylation of p38 MAPK at tyrosine 182, wh ich is required for the kinase's activation, occurred during ischemia only when protection from preconditioning was evident. In a second stu dy, changes in osmotic fragility were measured during simulated ischem ia in rabbit cardiomyocytes, Reduced fragility in ischemically precond itioned myocytes could be completely abolished by the specific p38 MAP K inhibitor SB-203580. In contrast, anisomycin, an activator of p38 MA PK and JUN kinase pathways, was found to be as protective as ischemic preconditioning, We conclude that p38 MAPK phosphorylation correlates with preconditioning's protection, and that its activation may be an i mportant step in the signal transduction cascade of ischemic precondit ioning. (C) 1997 Academic Press Limited.