Effects of Ischemia on Cardiomyocyte Connexin-43 Distribution and Phosphorylation Studied in in vivo and in vitro Models

  • Stéphane Tanguy
  • Madhumathy Jeyaraman
  • Bradley W. Doble
  • Zhisheng Jiang
  • Robert R. Fandrich
  • Elissavet Kardami
Part of the Progress in Experimental Cardiology book series (PREC, volume 10)

Summary

The gap junction protein connexin-43 (Cx43) exists mainly in the phosphory-lated state in the normal heart. We have investigated short-term effects of ischemia on cardiac Cx43 phosphorylation and distribution, in four models: global ischemia of the ex vivo perfused heart, left ventricular ischemia induced by irreversible coronary ligation in vivo, simulated ischemia on isolated adult myocyte pellets, and neonatal cardiomyocytes incubated in a hypoxia chamber. Antibody AB. 13-800 that recognizes specifically the 41kDa nonphospho-rylated form of cardiac Cx43 labeled intercalated discs (ICDs) in myocytes from perfused rat hearts subjected to 30min global ischemia; also in myocytes at the infarct border 6 hours post-infarction. Ischemia induced a sharp increase in the 41 kDa Cx43 from perfused hearts, isolated adult myocyte pellets and neonatal myocyte cultures subjected to hypoxia. The protein phosphatase type 1/2A inhibitors okadaic acid and calyculin A, tested in the in vitro models, decreased ischemia-induced Cx43 dephosphorylation. The 41 kDa Cx43 was present in both Triton-soluble as well as Triton-insoluble (enriched in ICDs) cardiac membrane fractions, assessed by western blotting. We conclude that ischemia causes dephosphorylation of car-diomyocyte Cx43 in vivo as well as in vitro, and that this phenomenon occurs irrespectively of stage (neonatal or adult) or presence of cell contact. Cx43 dephosphorylation occurs at ICDs, is mediated at least in part by PPl/2-type phosphatases, and would be expected to affect GJ function and contribute to ischemia-induced conductance and contractile changes.

Key words

Ischemia models gap junctions phosphorylation 

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Copyright information

© Springer Science+Business Media Dordrecht 2004

Authors and Affiliations

  • Stéphane Tanguy
    • 1
  • Madhumathy Jeyaraman
    • 1
  • Bradley W. Doble
    • 1
  • Zhisheng Jiang
    • 1
  • Robert R. Fandrich
    • 1
  • Elissavet Kardami
    • 1
  1. 1.Institute of Cardiovascular Sciences, Departments of Human Anatomy and Cell Sciences and PhysiologyUniversity of ManitobaWinnipegCanada

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