REGULAR ARTICLE Cardiac telocytes — their junctions and functional implications

Abstract Telocytes (TCs) form a cardiac network of inter-stitial cells. Our previous studies have shown that TCs are involved in heterocellular contacts with cardiomyocytes and cardiac stem/progenitor cells. In addition, TCs frequently establish ‘stromal synapses ’ with several types of immuno-reactive cells in various organs (www.telocytes.com). Using electron microscopy (EM) and electron microscope tomog-raphy (ET), we further investigated the interstitial cell net-work of TCs and found that TCs form ‘atypical ’ junctions with virtually all types of cells in the human heart. EM and ET showed different junction types connecting TCs in a network (puncta adhaerentia minima, processus adhaer-entes and manubria adhaerentia). The connections between TCs and cardiomyocytes are ‘dot ’ junctions with nanocon-tacts or asymmetric junctions. Junctions between stem cells and TCs are either ‘stromal synapses ’ or adhaerens junc-tions. An unexpected finding was that TCs have direct cell– cell (nano)contacts with Schwann cells, endothelial cells and pericytes. Therefore, ultrastructural analysis proved that the cardiac TC network could integrate the overall ‘infor-mation ’ from vascular system (endothelial cells and peri-cytes), nervous system (Schwann cells), immune system (macrophages, mast cells), interstitium (fibroblasts, extra-cellular matrix), stem cells/progenitors and working cardio-myocytes. Generally, heterocellular contacts occur by means of minute junctions (point contacts, nanocontacts and pla-nar contacts) and the mean intermembrane distance is with-in the macromolecular interaction range (10–30 nm). In conclusion, TCs make a network in the myocardial interstitium, which is involved in the long-distance intercel-lular signaling coordination. This integrated interstitial sys-tem appears to be composed of large homotropic zones (TC–TC junctions) and limited (distinct) heterotropic zones (heterocellular junctions of TCs)