Objective. We investigated whether the aging-related decrease in gap junction expression affects myocardial response against ischemia-reperfusion injury of the rabbit myocardium. Methods. Henseleit solution via a Langendorff apparatus, and were divided into five groups as follows: 7 mature hearts served as mature controls (Group A), 7 mature hearts underwent ischemic preconditioning (IPC) consisting of two cycles of global ischemia for 5min followed by reperfusion for 5min (Group B), 7 aged

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... ts served as aged control (Group C), 7 aged hearts underwent IPC (Group D) and 7 mature hearts received 1mM of gap junction uncoupler heptanol for 5min (Group E). Then, all hearts were subjected to 1h of left anterior descending coronary artery occlusion followed by 1h of reperfusion. Left ventricular pressure, ischemic zone monophasic action potential and coronary flow were measured throughout the experiment and the infarct size (IS) was determined at the end of the experiment. Gap junction expression was aged hearts was less prominent than in mature ones. Conclusion. These data suggested that aged myocardium might be more tolerant of ischemic insult than that of mature heart, and that the mechanism might be related to the aging-related change of gap junction expression. Jpn. J.