Selective activation of adenosine A3 receptors with N6-(3-chlorobenzyl)-5'-N-methylcarboxamidoadenosine (CB-MECA) provides cardioprotection via KATP channel activation.
OBJECTIVE
The aim of this study was to characterize the adenosine A3 receptor agonist, N6-(3-chlorobenzyl)-5'-N-methylcarboxamidoadenosine (CB-MECA), evaluate its ability to reduce myocardial ischemia/reperfusion injury and determine the role of KATP-channel activation in A3 receptor-mediated cardioprotection.


METHODS
Binding affinities and adenylate cyclase inhibition were examined in CHO cells expressing rabbit recombinant adenosine A1 or A3 receptors. Infarct size (normalized for area-at-risk; % IA/AAR) was measured in buffer-perfused rabbit hearts exposed to 30-min regional ischemia and 120 min of reperfusion.


RESULTS
CB-MECA was 100-fold selective for A3 vs. A1 receptors (A3 Ki: 1 nM; A1 Ki: 105 nM). Five-min perfusion with CB-MECA before ischemia/reperfusion elicited a concentration-dependent reduction in infarct size (EC50: 0.3 nM). The CB-MECA-dependent cardioprotection (control: 58 +/- 2; CB-MECA: 21 +/- 3% IA/AAR) was unchanged by an A1-selective concentration of the antagonist, BWA1433, but was completely prevented (P < 0.05) by a nonselective (A1/A3) concentration (55 +/- 6% IA/AAR). The KATP channel inhibitors, glibenclamide and 5-HD, had no effect on control infarct size, yet significantly (P < 0.05) blunted the CB-MECA-dependent cardioprotection (glibenclamide: 49 +/- 6; 5-HD: 58 +/- 4% IA/AAR).


CONCLUSIONS
CB-MECA is a novel 100-fold A3 receptor-selective agonist which should prove useful for elucidating A3-dependent mechanisms in the rabbit heart. Selective stimulation of adenosine A3 receptors with CB-MECA reduces myocardial ischemia/reperfusion injury via a mechanism which involves activation of KATP channels.
Tracey
W R
WR
Department of Cardiovascular and Metabolic Diseases, Pfizer Inc., Groton, CT 06340, USA. w_ross_tracey@groton.pfizer.com
Magee
W
W
Masamune
H
H
Oleynek
J J
JJ
Hill
R J
RJ
D000241:Adenosine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology; D001667:Binding, Competitive; D016466:CHO Cells; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D000242:Cyclic AMP / Q000378:metabolism; D003652:Decanoic Acids / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005905:Glyburide / Q000494:pharmacology; D006880:Hydroxy Acids / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D015428:Myocardial Reperfusion Injury / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control*; D009206:Myocardium / Q000378:metabolism / Q000473:pathology; D010477:Perfusion; D015221:Potassium Channels / Q000187:drug effects* / Q000378:metabolism; D011817:Rabbits; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D014970:Xanthines / Q000494:pharmacology
D000889:Anti-Arrhythmia Agents; C116825:CB MECA; D003652:Decanoic Acids; D006880:Hydroxy Acids; D007004:Hypoglycemic Agents; D015221:Potassium Channels; D043684:Receptor, Adenosine A3; D018047:Receptors, Purinergic P1; D014970:Xanthines; D005576:Colforsin; C052853:5-hydroxydecanoic acid; C053414:BW A1433U; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D000241:Adenosine; D005905:Glyburide