Activation of ecto-5'-nucleotidase by protein kinase C and its role in ischaemic tolerance in the canine heart

1 Ischaemic preconditioning (IF) protects the myocardium against irreversible ischaemic injury by activating protein kinase C (PKC). The mechanism by which PKC protects the myocardium is unknown. We have shown that PKC increases the activity of ecto-5'-nucleotidase (ecto-5'-N) and thereby the production of adenosine in cardiomyocytes which may protect the myocardium against ischaemia-reperfusion injury in vivo. 2 The objective of this study was to elucidate the possible role of PKC-induced activation of ecto-5'-N in the cardioprotection associated with IF in the canine heart. 3 IP increased the activities of both ecto-5'-N and PKC, and minimized ischaemic damage (infarct size: 7.5+/-1.8 vs. 42.3+/-2.8%, P<0.01 vs. the control group). Treatment with the PKC activator (4 beta-phorbol 12-myristate-13-acetate) also reduced infarct size (13.5+/-2.9%, P<0.01 vs. the control group). 8-Sulfophenyltheophylline (an antagonist of adenosine receptors) or alpha,beta-methyleneadenosine 5'-diphosphate (an inhibitor of ecto-5'-N) eliminated the cardioprotective effect of the PKC activator (infarct size: 36.6+/-3.9 and 34.7+/-4.2%, respectively), suggesting that PMA limits infarct size by increasing the activity of ecto-5'-N and the adenosine level. 4 The PMA-induced cardioprotection was blunted by GF109203X (an inhibitor of PKC, infarct size: 36.2+/-3.1%), but not by pretreatment with dexamethasone (infarct size, 14.2+/-2.6%). 5 We conclude that the PMA- and IP-induced cardioprotection is attributable to phosphorylation and activation of ecto-5'-N.