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Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a myocardial disease characterized by fibro-fatty replacement of myocardium in the right ventricular free wall and frequently results in life-threatening ventricular arrhythmias and sudden cardiac death. A heterozygous missense mutation in the transmembrane protein 43 (TMEM43) gene, p.S358L, has been genetically identified to cause autosomal dominant ARVC type 5 in a founder population from the island of Newfoundland, Canada. Little is known about the function of the TMEM43 protein or how it leads to the pathogenesis of ARVC. We sought to determine the distribution of TMEM43 and the effect of the p.S358L mutation on the expression and distribution of various intercalated (IC) disc proteins as well as functional effects on IC disc gap junction dye transfer and conduction velocity in cell culture. Through Western blot analysis, transmission electron microscopy (TEM), immunofluorescence (IF), and electrophysiological analysis, our results showed that the stable expression of p.S358L mutation in the HL-1 cardiac cell line resulted in decreased Zonula Occludens (ZO-1) expression and the loss of ZO-1 localization to cell-cell junctions. Junctional Plakoglobin (JUP) and α-catenin proteins were redistributed to the cytoplasm with decreased localization to cell-cell junctions. Connexin-43 (Cx43) phosphorylation was altered, and there was reduced gap junction dye transfer and conduction velocity in mutant TMEM43-transfected cells. These observations suggest that expression of the p.S358L mutant of TMEM43 found in ARVC type 5 may affect localization of proteins involved in conduction, alter gap junction function and reduce conduction velocity in cardiac tissue. [ABSTRACT FROM AUTHOR]