title: Sodium hydrogen exchange 1 (NHE-1) regulates connexin 43 expression in cardiomyocytes via reverse mode sodium calcium exchange and c-Jun NH2-terminal kinase-dependent pathways.
abstract: Connexin 43, the major connexin isoform in gap junctions of cardiac ventricular myocytes, undergoes changes in distribution and expression in cardiac diseases. The Na(+)-H(+) exchanger (NHE-1), a key mediator of hypertrophy and heart failure, has been shown to be localized in the cardiomyocyte gap junctional regions; however, whether NHE-1 regulates gap junction proteins in the hypertrophied cardiomyocyte is not known. To address this question, neonatal rat ventricular myocytes were treated with phenylephrine (PE) for 24 h to induce hypertrophy. Increased Cx43 expression observed with PE treatment (132.4 +/- 6.3% compared to control; P < 0.05) was further significantly augmented by the specific NHE-1 inhibitor EMD87580 [N-[2-methyl-4,5-bis(methylsulfonyl)-benzoyl]-guanidine hydrochloride] (173.2 +/- 8.7% increase compared to control; P < 0.05 versus PE), an effect that was mimicked by another NHE-1 inhibitor cariporide [4-isopropyl-3-(methylsulfonyl)benzoyl-guanidine methanesulfonate]. PE-induced hypertrophy was associated with mitogen-activated protein kinase c-Jun NH(2)-terminal kinase (JNK) 1/2 activation, whereas inhibition of JNK1/2 with either SP600125 [anthra(1,9-cd)pyrazol-6(2H)-one 1,9-pyrazoloanthrone] or small interfering RNA significantly increased PE-induced up-regulation of Cx43 protein levels. Inhibition of reverse mode Na(+)-Ca(2+) exchange (NCX) with KB-R7943 [2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea mesylate] partially reversed JNK1/2 activation (195.2 +/- 21.4 versus 143.7 +/- 14.4% with KB-R7943; P < 0.05) and augmented up-regulation of Cx43 protein (121.1 +/- 8.3 versus 215.9 +/- 25.6% with KB-R7943; P < 0.05) in the presence of PE. Our results demonstrate that NHE-1 negatively regulates Cx43 protein expression in PE-induced cardiomyocyte hypertrophy via a JNK1/2-dependent pathway, which is probably activated by reverse mode NCX activity.
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada.
authors.forename: Seta
authors.initials: S
authors.lastname: Stanbouly
authors.forename: Lorrie A
authors.initials: LA
authors.lastname: Kirshenbaum
authors.forename: Douglas L
authors.initials: DL
authors.lastname: Jones
authors.forename: Morris
authors.initials: M
authors.lastname: Karmazyn
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D018031:Connexin 43 / Q000032:analysis / Q000235:genetics*; D048055:Mitogen-Activated Protein Kinase 8 / Q000502:physiology*; D048056:Mitogen-Activated Protein Kinase 9 / Q000502:physiology*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D019831:Sodium-Calcium Exchanger / Q000502:physiology*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000502:physiology*
chemical_list: D018031:Connexin 43; D019831:Sodium-Calcium Exchanger; D017923:Sodium-Hydrogen Exchangers; C069139:growth factor-activatable Na-H exchanger NHE-1; D010656:Phenylephrine; D048056:Mitogen-Activated Protein Kinase 9; D048055:Mitogen-Activated Protein Kinase 8