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 NH2-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+-Ca2+ 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.
Footnotes
-
This work was supported by a grant from the Canadian Institutes of Health Research. S.S. was supported by the Heart and Stroke Foundation of Ontario Program Grant in Heart Failure and by the Schulich School of Medicine and Dentistry.
-
L.A.K. is Canada Research Chair in Molecular Cardiology.
-
M.K. is Canada Research Chair in Experimental Cardiology.
-
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
-
doi:10.1124/jpet.108.140228.
-
ABBREVIATIONS: Cx43, connexin 43; EMD87580, N-[2-methyl-4,5-bis(methylsulfonyl)-benzoyl]-guanidine hydrochloride; JNK, c-Jun NH2-terminal kinase; KB-R7943, 2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea mesylate; NHE-1, sodium-hydrogen exchanger-isoform 1; PE, phenylephrine; NCX, sodium calcium exchanger; PD98059, 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; siRNA, small interfering RNA; SB203580, 4-(4-fluorophenyl)-2-(4-methylsulfinyl phenyl)-5-(4-pyridyl)-1H-imidazole; SN-6, 2-[4-(4-nitrobenzyloxy)benzyl]thiazolidine-4-carboxylic acid ethyl ester; SP600125, anthra(1,9-cd)pyrazol-6(2H)-one 1,9-pyrazoloanthrone; ERK, extracellular signal-regulated kinase; PBS, phosphate-buffered saline; MAPK, mitogen-activated protein kinase.
- Received April 20, 2008.
- Accepted July 22, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
JPET articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|