Cardiac preconditioning with 4-h, 17°C ischemia reduces [Ca2+]i load and damage in part via KATP channel opening

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Abstract
Brief ischemia before normothermic ischemia protects hearts against reperfusion injury (ischemic preconditioning, IPC), but it is unclear whether it protects against long-term moderate hypothermic ischemia. We explored in isolated guinea pig hearts1) the influence of two 2-min periods of normothermic ischemia before 4 h, 17°C hypothermic ischemia on cardiac cytosolic [Ca2+], mechanical and metabolic function, and infarct size, and 2) the potential role of KATP channels in eliciting cardioprotection. We found that IPC before 4 h moderate hypothermia improved myocardial perfusion, contractility, and relaxation during normothermic reperfusion. Protection was associated with markedly reduced diastolic [Ca2+] loading throughout both hypothermic storage and reperfusion. Global infarct size was markedly reduced from 36 ± 2 (SE)% to 15 ± 1% with IPC. Bracketing ischemic pulses with 200 μM 5-hydroxydecanoic acid or 10 μM glibenclamide increased infarct size to 28 ± 3% and 26 ± 4%, respectively. These results suggest that brief ischemia before long-term hypothermic storage adds to the cardioprotective effects of hypothermia and that this is associated with decreased cytosolic [Ca2+] loading and enhanced ATP-sensitive K channel opening.