SINO-ATRIAL NODE TELOCYTES IN THE HUMAN HEART. MORPHOLOGICAL EVIDENCE FOR PACEMAKING AND CONDUCTION PROPERTIES

Abstract

The sinus node (SN) is built predominantly from pacemaking P-cells, transient T-cells, and Purkinje-like cells located on the periphery of the node. P-cells, especially in the center of SN, are surrounded by dense hardfiber fibrous tissue and do not contact with T-cells. We come up with a hypothesis that in the SN there are telocytes that may play role in electrical impulse conduction from pacemaking cells to contracting myocardium. Aim. Morphological analysis of telocytes in SN. Material and methods. Histological and immune-histochemical study of SN done on 10 autopsies. The double trace method was used, with combinations of primary antibodies to HCN4/connexin43 and CD34/connexin43. Confocal laser microscopy with 4 cocktails of antibodies to CD34/S100, CD34/connexin43, SMA/connexin43, S100/vimentin was done in 3 among 10 cases. Additional tissue specimens from SN of 3 other patients underwent electronic microscopy and immune cytochemistry analysis with HCN4. Results. In all studied SN, there were cells with immune phenotype of telocytes. In the center of the node, their number was 2 times more than in periphery (20,3±4,8 versus 10,8±4,4 cells in х400). Telocytes had dense contacts with P-cells, contracting myocardium, vessels, and expressed HCN4. Their ultrastructural characteristics completely resembled telocytes that are found in other organs and other heart tissues. Conclusion. Another type of cells was found, able to conduct and, probably, generate electrical impulse in the SN. In our opinion, electrical heterogeneity of the SN might be explained by the presence of telocytes.