Protective roles of adenosine A1, A2A, and A3 receptors in skeletal muscle ischemia and reperfusion injury

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 A(3) receptor-selective agonist 2-chloro-N-6-(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 A(3) receptor antagonist 3-ethyl-5-benzyl-2-methyl-6phenyl- 4-phenylethynyl-1,4-(+/-)-dihydropyridine-3,5-dicarboxylate (MRS-1191; 0.05 mg/kg). The adenosine A(1) receptor agonist 2-chloro-N6-cyclopentyladenosine (CCPA; 0.05 mg/kg) also exerted a cytoprotective effect, which was selectively blocked by the A1 antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.2 mg/kg). The adenosine A(2A) receptor agonist 2-p-(2-carboxyethyl) phenethylamino5' -N-ethylcarboxamidoadenosine (CGS-21680; 0.07 mg/kg)-induced decrease in skeletal muscle injury was selectively blocked by the A2A antagonist 2-(2-furanyl)-7-[ 3-(4-methoxyphenyl) propyl]-7Hpyrazolo[ 4,3-e] [1,2,4] triazolo[ 1,5-C] pyrimidin-5-amine (SCH-442416; 0.017 mg/kg). The protection induced by the A(3) receptor was abrogated in phospholipase C-beta 2/beta 3 null mice, but the protection mediated by the A(1) or A(2A) receptor remained unaffected in these animals. The adenosine A(3) receptor is a novel cytoprotective receptor that signals selectively via phospholipase C-beta and represents a new target for ameliorating skeletal muscle injury.