K ATP opener-induced delayed cardioprotection: involvement of sarcolemmal and mitochondrial K ATP channels, free radicals and MEK1/2

Abstract

Previous studies have demonstrated the importance of the sarcolemmal and/or the mitochondrial KATP channel (sKATP and mKATP, respectively) in mediating delayed cardioprotection induced by opioids, bradykinin, adenosine or the KATP-channel opener (KCO), diazoxide. However, the ability of other KCOs, such as the putative sKCO P-1075 or the putative mKCO BMS-191095, to induce delayed cardioprotection has not been tested. In this study, rats were randomly divided and treated with P-1075 (1 μg/kg), BMS-191095 (BMS, 1 mg/kg), diazoxide (3.5 mg/kg) or vehicle. Selective blockers were also administered 5 min prior to KCO or vehicle. These included the sKATP antagonist (HMR-1098 (HMR, 6 mg/kg)), the mKATP antagonist (5-hydroxydecanoic acid (5-HD, 10 mg/kg)), the oxygen radical scavenger (N-2-mecaptopropionyl-glycine (2-MPG, 20 mg/kg)) or the MEK1/2 inhibitor (PD-98059 (PD, 1 mg/kg)). Twenty-four hours later, rats were subjected to 30-min ischemia and 2-h reperfusion, followed by infarct size assessment. P-1075, BMS or diazoxide treatment produced similar reductions in infarct size as compared to vehicle (37.2 ± 2.3%*, 40.7 ± 1.5%*, 35.6 ± 3.6%* vs. 59.8 ± 1.8%, P < 0.05, respectively). HMR administration before P-1075 and diazoxide abolished delayed cardioprotection, but not BMS-induced infarct size reduction (56.1 ± 1.1%, 54.9 ± 3.3%, 41.0 ± 1.7%*, respectively). Administration of 5-HD, 2-MPG or PD prior to the three KATP openers abolished delayed cardioprotection. These data imply BMS-191095 has a selective mitochondrial site of action, perhaps the mKATP channel, whereas diazoxide and P-1075 affect both the sKATP and mKATP channels. All three KCO also require an initial oxygen-derived free radical (OFR) burst and MEK1/2 activation to trigger delayed cardioprotection.