Rate of Rise of Purkinje and Transitional Cells Action Potential and the Propagation Across the Purkinjemyocardium Junction

On a papillary muscle and its corresponding false tendon from the dog heart, the transmembrane potentials of Purkinje and “transitional cells” were recorded.The action potentials recorded along the surface of the false tendon had the shape, amplitude and rate of rise similar to those of the typical Purkinje fiber responses. The RMP of cells from the false tendon have also approximately the same value than that of Purkinje cells (FIGS. 2 and 3). When the exploring microelectrode reached the “terminal Purkinje” fibers their membrane characteristics decreased slightly. The magnitude of these differences was even greater when recording from transitional cells located within the junctional region (FIGS. 2f and 3f).Variables of different nature were introduced in order to study the relationship between the rate of rise of action potentials from transitional cells and the propagation of impulses through the junctional region of Purkinje and myocardial cells. a) Progressive increase in the frequency of stimulation (FIGS. 4 and 5), b) diminution in external NaC1 (FIG. 6), c) lack of calcium (FIG. 10), d) anoxia (FIG. 8), e) low temperatures (FIG. 7). All these variables produced a decrease in the rate of rise and amplitude of the initial component of a transitional potential and consequently the propagation through the junctional region was delayed or blocked (FIG. 1).Simultaneous recording from two transitional cells revealed that conduction velocity is slower in the junctional region than in the false tendon. This fact suggest that transitional potentials having a slow rate of rise and small amplitude may cause the delays or the blockages in propagation occurring in the junctional regions.