ABSTRACT
The concept of heart muscle as an antomical syncytium dominated cardiac electro-physiology for many years. When F. S. Sjostrand and E. Andersson demonstrated that cardiac cells are isolated functional units separated from each other by a cleft it became difficult to understand how the electrical impulse can propagate from cell to cell. It was found that Cyclic AMP (cAMP) increases the junctional conductance in cardiac tissues within seconds, supporting the view that the homonal system that uses cAMP as second messenger is integrated with the intercellular communication system mediated by gap junctions. The longitudinal redistribution of Lucifer Yellow CH in quiescent muscle trabeculae was followed with the cut-end method. For this, the muscle was pulled through a tight-fitting hole in a rubber membrane which separated a Perspex chamber into two compartments. Measurements of the intracellular longitudinal resistance in rat papillary muscles, using a modification of the technique described by S. Weidmann, showed a decline of intracellular resistance with isoproterenol.
