Interaction of Transmembrane Potentials in Canine Purkinje Fibers and at Purkinje Fiber-Muscle Junctions

Interactions between Purkinje fibers and ventricular muscle were studied in canine Purkinje-papillary muscle preparations. The change in duration of action potentials across the junctions between Purkinje fibers and papillary muscle was continuously graded, not abrupt. The transmembrane action potentials were longest in the false tendons and progressively shorter in more peripheral fibers. The responses of terminal Purkinje fibers and of neighboring muscle cells differed little in duration. The shortest action potentials were found in muscle fibers located in regions devoid of specialized tissue (tip of papillary muscle). These results suggest that the intercellular connections, including those at the junctions, offer relatively low resistance to current flow. During repolarization the current flowing between neighboring elements with intrinsically different repolarization times should therefore minimize the disparity in action potential durations on the two sides of the junctional site; a continuously graded change in duration would result. Because of this continuous gradation, premature ventricular responses initiated at the tip of the papillary muscle could be blocked, depending on the degree of prematurity, at various levels in muscle fibers functionally close to terminal Purkinje fibers or within the Purkinje system.