Abstract 5424: Selective Inhibition of Connexin 43 Hemichannels by Gap26 Confers Cardioprotection Against Myocardial Ischemia Injury
Connexins are the basic units in the composition of gap junction channels (GJC) but also of the unapposed hemichannels (Hc). Hc exert functions different from those achieved by GJC, mainly by providing a path between the cytosol and the extracellular space allowing movement of ions and other small molecules. In cardiac myocardium, opening of connexin 43 Hc (Cx43Hc) under ischemic stress contributes to irreversible tissue injury and cell death. Here, we hypothesized that Gap26, a synthetic structural-mimetic peptide deriving from Cx43 extracellular loop and selectively blocking Cx43Hc with little or no effect on GJC, confers resistance to isolated rat heart against ischemia injury and reduces the resulting infarct size. Langendorff isolated rat hearts were subjected to 40 min ischemia by left anterior descendent (LAD) coronary occlusion, followed by 180 min of reperfusion. Gap26 peptide (0.5 μg/ml) was introduced through the perfusion solution at 10 min before LAD occlusion (group 1) or 10 min before reperfusion (group 2). Infarct size was assessed on histological sections using Evans blue and triphenyltetrazolium chloride method and compared with control group where hearts were subjected to the same protocol but using Gap26-free solutions. As negative control, a scrambled sequence of the Gap26 peptide was also tested. Myocardial infarct size in groups 1 and 2 was considerably reduced by 60.1 ± 3.5 %, n = 9, P<0.05 and 65.0 ± 2.6 %, n = 7, P<0.05, respectively, compared to hearts from the control group. In addition, the zone of perfused myocardium in hearts of both group 1 and group 2 was significantly increased by 14.4 ± 8.1 %, n = 9, P<0.05 and 19.5 ± 5.4%, n = 7, P<0.05, respectively. No significant changes were observed in the size of the risk zone of group 1, increase of 1.5 ± 16.1%, n = 7, or group 2, decrease of 3.9 ± 10.2%, n = 9, in comparison with control hearts. Values obtained from group 1 and group 2 were not statistically different when compared to each other. We demonstrate, for the first time, that specific block of Cx43Hc in isolated rat heart confers resistance against ischemia/reperfusion injury. Our results show that Gap26 exerts protective effects against coronary occlusion-induced ischemia injury, whether administered before or after the initiation of ischemia.