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

Ischaemic preconditioning (IP) 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 . The objective of this study was to elucidate the possible role of PKC‐induced activation of ecto‐5′‐N in the cardioprotection associated with IP in the canine heart. 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 (4β‐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 α,β‐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. 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%). We conclude that the PMA‐ and IP‐induced cardioprotection is attributable to phosphorylation and activation of ecto‐5′‐N.British Journal of Pharmacology (1997) 120 , 273–281; doi: 10.1038/sj.bjp.0700890