In Swine Myocardium, the Infarct Size Reduction Induced by U-89232 is Glibenclamide Sensitive: Evidence That U-89232 is a Cardioselective Opener of ATP-Sensitive Potassium Channels

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Abstract
We determined whether U-89232, a derivative of the ATP-sensitive potassium (KATP) channel opener cromakalim, is cardioselective and whether its action on the myocardium is still sensitive to glibenclamide. Experiments were performed in open-chest pigs subjected to a 60-min occlusion of the left anterior descending coronary artery (LADCA) and to 2 h of reperfusion. Four groups of animals were studied (n = 6 each). Animals received either U-89232, 3 mg/kg i.v. over a 15-min period (U), or glibenclamide, a selective KATP channel blocker, 1 mg/kg i.v. over a 15-min period (GLI) before the LADCA occlusion. In the GLI + U group, first glibenclamide (1 mg/kg/15 min) and then U-89232 (3 mg/kg/15 min) were infused before the 60 min of ischemia. Saline-treated animals served as controls (CON). Hemodynamic parameters were continuously monitored. Regional contractile wall function was quantified with ultrasonic crystals aligned to measure wall thickening. At the end of the protocol, infarct size (IS, as percentage of risk region) was determined by incubating the myocardium with p-nitrobluetetrazolium. With comparable myocardium at risk, infusion of U-89232 before 60 min of LADCA occlusion significantly reduced infarct size (IS, 18.5 +/- 3.7%; p < 0.001 vs. 63.2 +/- 3.3% for the controls), whereas glibenclamide had no effect on infarct size (IS, 69.5 +/- 4.4%). The administration of glibenclamide before U-89232 infusion blocked the infarct size-reducing effect of U-89232 [IS, 61.2 +/- 9.1 (NS) vs. controls and p < 0.001 vs. U]. Infusion of U-89232 had no effect on hemodynamic parameters or on regional wall function. At least in a pig model, U-89232 appears to be a cardioselective KATP channel opener, because in the absence of hemodynamic alterations, it exhibits a profound cardioprotective effect, which is fully reversible by blocking KATP channels.