RESUMO
BACKGROUND: It has been suggested that gap-junctional conductance between cardiomyocytes is regulated through a specific ligand-receptor interaction between ATP and connexins. In this study we examined the localization of P2X1 ionotropic receptors and their relation to connexin43 in gap junctions in human left ventricles. METHODS AND RESULTS: Using immunohistochemistry, we detected P2X1 expression predominantly in the intercalated discs. Labelling of the P2X1 receptor and the gap junction protein connexin43 showed close association in some gap junctions, while in others the two proteins often appeared to be spatially discrete. Western blotting detected four major bands at 45, 60, 95 and 120 kDa in the protein extracts from human left ventricles corresponding to equivalent bands from rat vas deferens. The most prominent band in human left ventricles was at 95 kDa, possibly a dimer of the native P2X1 receptor, whereas in rat vas deferens it was at 60 kDa. After preincubation of the antibody with its epitope peptide, the 45 and 60 kDa bands almost disappeared and the 95 and 120 kDa bands were significantly attenuated. CONCLUSIONS: P2X1 receptors in human myocardium are densely localized in gap junctions at intercalated discs between muscle cells. Close association of P2X1 receptors and connexin 43 occurred in some regions of some gap junctions, but in others they were spatially separate. Little difference in the pattern of distribution of P2X1 receptors was found in failing left ventricles of patients with dilated cardiomyopathy, although Western blots showed an enhancement of P2X1 receptor protein.