Protective roles of adenosine A1, A2A, and A3receptors in skeletal muscle ischemia and reperfusion injury

Abstract

Although adenosine exerts cardio-and vasculoprotective effects, the roles and signaling mechanisms of different adenosine receptors in mediating skeletal muscle protection are not well understood. We used a mouse hindlimb ischemia-reperfusion model to delineate the function of three adenosine receptor subtypes. Adenosine A3receptor-selective agonist 2-chloro- N6-(3-iodobenzyl)adenosine-5′- N-methyluronamide (Cl-IBMECA; 0.07 mg/kg ip) reduced skeletal muscle injury with a significant decrease in both Evans blue dye staining (5.4 ± 2.6%, n = 8 mice vs. vehicle-treated 28 ± 6%, n = 7 mice, P < 0.05) and serum creatine kinase level (1,840 ± 910 U/l, n = 13 vs. vehicle-treated 12,600 ± 3,300 U/l, n = 14, P < 0.05), an effect that was selectively blocked by an A3receptor antagonist 3-ethyl-5-benzyl-2-methyl-6-phenyl-4-phenylethynyl-1,4-(±)-dihydropyridine-3,5-dicarboxylate (MRS-1191; 0.05 mg/kg). The adenosine A1receptor agonist 2-chloro- N6-cyclopentyladenosine (CCPA; 0.05 mg/kg) also exerted a cytoprotective effect, which was selectively blocked by the A1antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.2 mg/kg). The adenosine A2Areceptor agonist 2- p-(2-carboxyethyl)phenethylamino-5′- N-ethylcarboxamidoadenosine (CGS-21680; 0.07 mg/kg)-induced decrease in skeletal muscle injury was selectively blocked by the A2Aantagonist 2-(2-furanyl)-7-[3-(4-methoxyphenyl)propyl]-7H-pyrazolo[4,3-e] [1,2,4]triazolo[1,5-C]pyrimidin-5-amine (SCH-442416; 0.017 mg/kg). The protection induced by the A3receptor was abrogated in phospholipase C-β2/β3 null mice, but the protection mediated by the A1or A2Areceptor remained unaffected in these animals. The adenosine A3receptor is a novel cytoprotective receptor that signals selectively via phospholipase C-β and represents a new target for ameliorating skeletal muscle injury.