Role of activation of ectosolic 5'-nucleotidase in the cardioprotection mediated by opening of K+ channels

We tested the hypothesis that the opening of ATP-sensitive K+ channels contributes to activation of ectosolic 5'-nucleotidase and the infarct size-limiting effect of ischemic preconditioning. In open-chest dogs, the left anterior descending coronary artery was occluded four times for 5 min each, separated by a 5-min period of reperfusion (ischemic preconditioning, n = 8). After this procedure, the coronary artery was occluded for 90 min, followed by 6 h of reperfusion. Infarct size was smaller in this group than in the group (control, n = 8) with a 45-min interval instead of the ischemic preconditioning procedure (40.1 +/- 3.9 vs. 6.4 +/- 1.9%). Glibenclamide blunted the infarct size-limiting effect of ischemic preconditioning (infarct size, 37.3 +/- 5.8%; n = 7), and transient exposures to cromakalim and nicorandil mimicked it [infarct size, 10.1 +/- 3.1 (n = 7) and 11.1 +/- 2.7% (n = 8), respectively]. Ectosolic and cytosolic 5'-nucleotidase activity increased in the ischemic preconditioning group compared with that in the control group; this pre conditioning-induced increase in 5'-nucleotidase activity was blunted by glibenclamide (n = 5) and mimicked by cromakalim (n = 5) and nicorandil (n = 5). The infarct size-limiting effect due to cromakalim and nicorandil was blunted by alpha,beta-methyleneadenosine 5'-diphosphate, an inhibitor of ectosolic 5'-nucleotidase [infarct size, 37.7 +/- 5.6 (n = 9) and 36.8 +/- 4.8% (n = 7), respectively] and 8-sulfophenyltheophylline (infarct size with cromakalim, 44.7 +/- 4.6%; n = 7). We conclude that activation of ectosolic 5'-nucleotidase due to the openers of ATP-sensitive K+ channels contributes to the infarct size-limiting effect of ischemic preconditioning.