Abstract 3623: Selective Inhibition of Connexin 43 Hemichannels by GAP26 Confers Cardioprotection Against Ischemia-Reperfusion Injury: In vivo Study
Introduction: Connexins are the basic units in the composition of gap junction channels but also of unapposed hemichannels (Hc). Hc exert functions different from those achieved by gap junction channels, mainly by providing path between cytosol and extracellular space allowing movement of ions and other small molecules. In cardiac myocytes, connexin 43 Hc (Cx43Hc) are believed to be close during physiological conditions but open under ischemic stress.
Hypothesis: Here, we hypothesized that administration of Gap26, a synthetic structural-mimetic peptide deriving from Cx43 extracellular loop and selectively blocking Cx43Hc with little or no effect on gap junction channels, confers resistance to rat heart in vivo against ischemia injury and reduces the resulting infarct size.
Methods: Rat hearts were subjected to 40 min local ischemia by ligation of the left anterior descendent (LAD) coronary followed by 3 days of reperfusion. Gap26 peptide was administered as a bolus intravenous injection 10 min before LAD ligation (group 1) or 10 min before reperfusion (group 2). On day 3 post-ischemia, rats were sacrificed and infarct size was assessed on histological sections using triphenyltetrazolium method. As negative control, inactive scrambled Gap26 (sGap26) peptide was tested.
Results: Myocardial infarct size in groups 1 and 2 was reduced by 72.9±2.9 % (n=8, P<0.05) and 52.4±6.6 % (n=4, P<0.05), respectively, compared to hearts from untreated rats. In addition, the zone of perfused myocardium in hearts of both group 1 and group 2 was significantly increased by 28.0±4.1 % (n=8, P<0.05) and 11.2±2.6% (n=4, P<0.05), respectively. No significant changes were observed in the size of the zone at risk in group 1, decrease of 2.7±4.9% (n=8), or group 2, increase of 7.7±3.4% (n=4), in comparison with hearts of untreated rats. Values obtained from negative control groups, treated with inactive sGap26, did not statistically differ from those of untreated rats.
Conclusion: We demonstrate, for the first time, that specific block of Cx43Hc confers resistance to rat heart in vivo against ischemia/reperfusion injury. Results show that Gap26 exerts differential protective effects against ischemia/reperfusion injury when administered before or after the initiation of ischemia.