PRECONDITIONING CULTURED HUMAN PEDIATRIC MYOCYTES REQUIRES ADENOSINE AND PROTEIN-KINASE-C

We showed previously that 20 min of low-volume anoxia (''ischemia'') a nd 20 min of ''reperfusion'' preconditions quiescent pediatric myocyte cultures against damage resulting from 90 min of subsequent prolonged ischemia and 30 min of reperfusion. The purpose of this study was to assess the roles of adenosine and protein kinase C (PKC) in this preco nditioning model. Our results suggest that 1)preconditioned myocytes s ecrete a protective mediator(s) into the ''ischemic'' supernatant that is transferable to other cells, and adenosine is released into the su pernatant in quantities sufficient for adenosine-receptor activation; (2) preconditioning is inhibited by adenosine-receptor antagonism, and myocyte protection similar to preconditioning can be achieved with ex ogenously administered adenosine or adenosine-receptor stimulation; (3 ) briefischemic and adenosine-induced myocyte preconditioning is mimic ked by the phorbol ester 4 beta-phorbol 12-myristate 13-acetate (PKC a gonist) and inhibited by PKC antagonists; and (4) briefischemic and ad enosine-induced myocyte preconditioning both induce PKC translocation to myocyte membranes and increase the PKC phosphorylation rate. These data suggest that adenosine released from ischemic human pediatric myo cytes mediates preconditioning through activation of PKC.