Postconditioning protects rabbit hearts through a protein kinase C-adenosine A2b receptor cascade.
OBJECTIVE
Ischemic postconditioning protects the reperfused heart from infarction, and this protection is dependent on the occupancy of adenosine receptors. We further explored the role of adenosine receptors in this salvage.


METHODS
In situ rabbit hearts underwent 30 min of regional ischemia and 3 h of reperfusion, and postconditioning was effected with four cycles of 30-s reperfusion/30-s coronary artery occlusion at the end of ischemia.


RESULTS
Postconditioning reduced infarct size from 40.2+/-3.4% of the risk zone in untreated hearts to 15.5+/-2.5%. Protection by postconditioning was blocked by either the non-selective adenosine receptor blocker 8-p-(sulfophenyl)theophylline or the A2b-selective antagonist MRS 1754, injected intravenously 5 min before reperfusion. The protein kinase C (PKC) antagonist chelerythrine also aborted postconditioning's salvage, indicating a PKC-dependent mechanism. Neither the A1-selective antagonist 8-cyclopentyl-1,3-dipropylxanthine nor the A2a-selective antagonist 8-(13-chlorostyryl)caffeine had an effect on protection. The non-selective but A2b-potent adenosine agonist 5'-(N-ethylcarboxamido)adenosine (NECA) infused from 5 min before to 1h after reperfusion mimicked postconditioning's effect on infarct size (17.2+/-2.7% infarction) and MRS 1754 blocked the NECA-induced cardioprotection, confirming that A2b activation was protective. The PKC activator phorbol 12-myristate 13-acetate delivered just before reperfusion also duplicated the protective effect of postconditioning (16.3+/-4.1% infarction), and co-administration of the PKC antagonist chelerythrine aborted PMA's protection, confirming that the protection was the result of PKC activation. NECA's protective effect was not affected by chelerythrine, but rather MRS 1754 blocked PMA's salutary effect (42.8+/-1.0% infarction), suggesting that the A2b receptor's effect is under control of PKC. Finally, wortmannin, a blocker of phosphatidylinositol 3-kinase, also abrogated protection by PMA.


CONCLUSIONS
Salvage of ischemic myocardium by postconditioning is dependent on activation of A2b receptors, which in turn depends on activation of PKC. It is still unclear why PKC activation is required to make the heart's adenosine become protective.
Department of Physiology, University of South Alabama, College of Medicine, Mobile, AL 36688, United States.
Sebastian
S
Philipp
Xi-Ming
XM
Yang
Lin
L
Cui
Amanda M
AM
Davis
James M
JM
Downey
Michael V
MV
Cohen
D000081:Acetamides / Q000494:pharmacology; D000241:Adenosine / Q000819:agonists / Q000378:metabolism; D058917:Adenosine A2 Receptor Antagonists; D019830:Adenosine-5'-(N-ethylcarboxamide) / Q000494:pharmacology; D000470:Alkaloids; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001011:Aorta; D053119:Benzophenanthridines; D003250:Constriction; D020536:Enzyme Activators / Q000494:pharmacology; D005260:Female; D008297:Male; D009203:Myocardial Infarction / Q000201:enzymology* / Q000473:pathology; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D009206:Myocardium / Q000201:enzymology* / Q000473:pathology; D010477:Perfusion; D010617:Phenanthridines / Q000494:pharmacology; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011687:Purines / Q000494:pharmacology; D011817:Rabbits; D043704:Receptor, Adenosine A2B / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D000077191:Wortmannin; D014970:Xanthines / Q000494:pharmacology
D000081:Acetamides; D058917:Adenosine A2 Receptor Antagonists; D000470:Alkaloids; D000730:Androstadienes; D053119:Benzophenanthridines; D020536:Enzyme Activators; C423842:N-(4-cyanophenyl)-2-(4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)-phenoxy)acetamide; D010617:Phenanthridines; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011687:Purines; D043704:Receptor, Adenosine A2B; D014970:Xanthines; D019830:Adenosine-5'-(N-ethylcarboxamide); C051360:1,3-dipropyl-8-cyclopentylxanthine; C016299:chelerythrine; D011493:Protein Kinase C; D000241:Adenosine; D013755:Tetradecanoylphorbol Acetate; D000077191:Wortmannin