Down-regulation of Connexin43 in Early Myocardial Ischemia and Protective Effect by Ischemic Preconditioning in Rat Hearts In Vivo
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- Hatanaka Kazuhito
- Department of Forensic Medicine, Graduate School of Medicine, University of Tokyo
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- Kawata Hiroyuki
- The First Department of Internal Medicine, Nara Medical University
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- Toyofuku Toshihiko
- Departments of Internal Medicine and Therapeutics, and Pathophysiology, Osaka University Graduate School of Medicine
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- Yoshida Ken-ichi
- Department of Forensic Medicine, Graduate School of Medicine, University of Tokyo
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Abstract
Connexin 43 (Cx43), a primary component of gap junctions, contributes to intercellular electrochemical communication. Cx43 undergoes dephosphorylation in early ischemia. We examined whether Cx43 is degraded in association with dephosphorylation during early myocardial ischemia and whether ischemic preconditioning (IP) affects the degradation after rat coronary artery occlusion. Male Sprague-Dawley rats underwent coronary artery occlusion for 1, 2, or 3 hours, or for 1 hour following treatment either with a calcineurin inhibitor (cyclosporine A), proteasome inhibitor (PSI), or lysosomal inhibitor (E64c), or following IP alone or after protein kinase C (PKC) inhibitor (chelerythrine) pretreatment. The IP was afforded by three cycles of 3 minute ischemia and 5 minute reperfusion. A large portion of the phosphorylated Cx43 (pCx43) in the membrane fraction was dephosphorylated, while a small portion was degraded at 1 hour of ischemia. The effects of the inhibitors were dephosphorylation and degradation by calcineurin and proteasome/lysosome, respectively. IP suppressed the decrease in pCx43 and increase in dCx43, while only the former was inhibited by the PKC inhibitor chelerythrine. The Cx43 mRNA level was reduced at 3 hours, but not at 1 hour of ischemia, irrespective of IP. We believe that Cx43 is dephosphorylated and degraded in early ischemia, whereas Cx43 transcription was suppressed at a later phase of ischemia. <br>
Journal
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- Japanese Heart Journal
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Japanese Heart Journal 45 (6), 1007-1019, 2004
International Heart Journal Association