Published online before print July 31, 2008, doi: 10.1161/CIRCRESAHA.108.179069
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© 2008 American Heart Association, Inc.
Cellular Biology |
RXP-E
A Connexin43-Binding Peptide That Prevents Action Potential Propagation Block
From the Departments of Pharmacology (R.L., R.V., W.C.) and Microbiology/Immunology (S.M.T.), State University of New York Upstate Medical University, Syracuse; Danish National Research Foundation Centre for Cardiac Arrhythmias and Department of Biomedical Sciences (K.P., M.S.N.), Faculty of Health Sciences, University of Copenhagen, Denmark; and Center for Arrhythmia Research (J.J., M.D.), Division of Cardiovascular Medicine, University of Michigan, Ann Arbor.
Correspondence to Mario Delmar, MD, PhD, Center for Arrhythmia Research, Division of Cardiovascular Medicine, University of Michigan, 5025 Venture Dr, Ann Arbor MI 48108. E-mail mdelmar{at}umich.edu
Gap junctions provide a low-resistance pathway for cardiac electric propagation. The role of GJ regulation in arrhythmia is unclear, partly because of limited availability of pharmacological tools. Recently, we showed that a peptide called "RXP-E" binds to the carboxyl terminal of connexin43 and prevents chemically induced uncoupling in connexin43-expressing N2a cells. Here, pull-down experiments show RXP-E binding to adult cardiac connexin43. Patch-clamp studies revealed that RXP-E prevented heptanol-induced and acidification-induced uncoupling in pairs of neonatal rat ventricular myocytes. Separately, RXP-E was concatenated to a cytoplasmic transduction peptide (CTP) for cytoplasmic translocation (CTP–RXP-E). The effect of RXP-E on action potential propagation was assessed by high-resolution optical mapping in monolayers of neonatal rat ventricular myocytes, containing 
20% of randomly distributed myofibroblasts. In contrast to control experiments, when heptanol (2 mmol/L) was added to the superfusate of monolayers loaded with CTP–RXP-E, action potential propagation was maintained, albeit at a slower velocity. Similarly, intracellular acidification (pHi 6.2) caused a loss of action potential propagation in control monolayers; however, propagation was maintained in CTP–RXP-E–treated cells, although at a slower rate. Patch-clamp experiments revealed that RXP-E did not prevent heptanol-induced block of sodium currents, nor did it alter voltage dependence or amplitude of Kir2.1/Kir2.3 currents. RXP-E is the first synthetic molecule known to: (1) bind cardiac connexin43; (2) prevent heptanol and acidification-induced uncoupling of cardiac gap junctions; and (3) preserve action potential propagation among cardiac myocytes. RXP-E can be used to characterize the role of gap junctions in the function of multicellular systems, including the heart.
Key Words: Cx43CT • particle–receptor interaction • gap junctions • connexin43 • rotigaptide
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