title: Ischemia-induced dephosphorylation of cardiomyocyte connexin-43 is reduced by okadaic acid and calyculin A but not fostriecin.
abstract: The gap junction protein connexin-43 (Cx43) exists mainly in the phosphorylated state in the normal heart, while ischemia induces dephosphorylation. Phosphatase(s) involved in cardiac Cx43 dephosphorylation have not as yet been identified. We examined the acute effects of ischemia on the dephosphorylation of the gap junction protein connexin-43 in isolated adult cardiomyocytes and isolated perfused hearts. In addition we tested the effectiveness of protein phosphatase 1 and 2A (PP1/2A) inhibitors in preventing Cx43 dephosphorylation. In both models, significant accumulation of the 41 kDa non-phosphorylated Cx43, accompanied by decreased relative levels of the 43-46 kDa phosphorylated Cx43, was observed at 30 min of ischemia. Okadaic acid decreased ischemia-induced Cx43 dephosphorylation; it also decreased the accumulation of non-phosphorylated Cx43 at the intercalated discs of myocytes in the whole heart. Calyculin A, but not fostriecin, also decreased ischemia-induced Cx43 dephosphorylation in isolated cardiomyocytes. It is concluded that isolated adult myocytes respond to ischemia in a manner similar to whole hearts and that ischemia-induced dephosphorylation of Cx43 is mediated, at least in part, by PP1-like phosphatase(s).
authors.affiliation: Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, University of Manitoba, Winnipeg, Canada.
authors.forename: Madhumathy
authors.initials: M
authors.lastname: Jeyaraman
authors.forename: Stéphane
authors.initials: S
authors.lastname: Tanguy
authors.forename: Robert R
authors.initials: RR
authors.lastname: Fandrich
authors.forename: Anton
authors.initials: A
authors.lastname: Lukas
authors.forename: Elissavet
authors.initials: E
authors.lastname: Kardami
mesh_terms: D000475:Alkenes / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D018031:Connexin 43 / Q000378:metabolism*; D017629:Gap Junctions / Q000378:metabolism; D015870:Gene Expression; D007511:Ischemia / Q000378:metabolism*; D008387:Marine Toxins; D032383:Myocytes, Cardiac / Q000378:metabolism*; D019319:Okadaic Acid / Q000494:pharmacology*; D010080:Oxazoles / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011090:Polyenes; D011753:Pyrones; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000475:Alkenes; D018031:Connexin 43; D008387:Marine Toxins; D010080:Oxazoles; D011090:Polyenes; D011753:Pyrones; D019319:Okadaic Acid; C059041:calyculin A; C040313:fostriecin