IMMUNOHISTOCHEMICAL LOCALIZATION OF GAP JUNCTION PROTEIN CHANNELS IN HAMSTER SINOATRIAL NODE IN CORRELATION WITH ELECTROPHYSIOLOGIC MAPPINGOF THE PACEMAKER REGION

Introduction: Gap junction proteins are thought to form the low resist ance pathways that connect neighboring cells within the sineatrial nod e, and to mediate pacemaker synchronization. Methods and Results: We h ave carried out microelectrode mapping experiments of the hamster sino atrial region to localize the primary pacemaker area for subsequent li ght, electron, and immunofluorescence microscopic studies aimed at tes ting the hypothesis that the major cardiac gap junction protein (conne xin43) is present in such an area. The site of earliest activation is unifocal and the pattern of activation, obtained by multiple sequentia l microelectrode recordings of the sinoatrial region, is qualitatively similar to that previously described for other species. However, quan titatively, the impulse transmission time from the primary pacemaker a rea to the crista (sulcus) terminalis in the hamster sinoatrial node i s about 50% briefer than that of the guinea pig and five times faster than that of the rabbit. Immunolocalization studies in the hamster sin oatrial node using anti-connexin43 antisera demonstrated specific stai ning at the areas of cell-to-cell apposition and suggested that the ap parently high degree of electrical coupling in this tissue is the resu lt of abundant connexin43 expression. The immunofluorescence data were supported by light microscopic studies, which demonstrated the typica l morphologic characteristics of sinus nodal cells in the pacemaker ar ea. In addition, an electron microscopic study of the sinoatrial regio n revealed the presence of gap junctions in the junctional complex at areas of cell-to-cell contact. Conclusion: Our results demonstrate tha t cells in the sinoatrial region of the hamster heart are electrically well coupled and strongly suggest that such coupling is mediated by g ap junctional channels formed by connexin43.