Electrical interaction between cardiomyocyte sheets separated by non-cardiomyocyte sheets in heterogeneous tissues.

Electrical coupling between cardiomyocytes is important in synchronous beating and normal heart functions. Cardiomyocytes are also electrically coupled to non-cardiomyocytes. The electrical interactions between cardiomyocytes and non-cardiomyocytes, or those between separated cardiomyocytes, are important for normal heart function because abnormalities of the coupling and variation of the cell population induce pathological heart functions and arrhythmias. In this study the three-dimensional time course of the electrical interaction between two rat neonatal cardiomyocyte sheets separated by non-cardiomyocyte sheets was analysed by a multiple-electrode extracellular recording system. The two cardiomyocyte sheets separated by a single- or double-layered mouse fibroblast NIH3T3 cell sheet coupled electrically at 113 +/- 28 or 287 +/- 87 min after layering, respectively. The time course of the electrical coupling, when the single-layer NIH3T3 cell sheet was inserted, is similar to that of a layered cardiomyocyte sheet. Immunocytological analysis and dye transfer assay suggested the formation of gap junctions at heterocellular junctions of cardiomyocytes and NIH3T3 cells. On the other hand, when a double-layered NIH3T3 cell sheet was inserted, an incomplete electrical coupling of two cardiomyocyte sheets, including a conduction delay, was observed. The electrical coupling of cardiomyocyte sheets was completely blocked (conduction block) by insertion of a triple-layered NIH3T3 cell sheet, a communication-defective HeLa cell sheet or a Ca(2+)-antagonist LaCl(3)-treated cell sheet. These electrophysiological analyses of heterogeneously stacked cell sheets might provide insights into complex electrical conduction systems that resemble those of native or damaged heart and transplanted tissues.