Effect of 2,4 Dinitrophenol on Electrical Activity in Purkinje and Ventricular Muscle Fibers of Hog Heart

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Abstract
DNP (2,4 dinitrophenol), in concentrations of 2 to 5 x 10-5 M produced changes in transmembrane action potential in both the Purkinje and ventricular muscle fibers of the isolated perfused hog heart; however, the time of initiation and rate of change of the different phases of the action potential in the two fibers varied. In the Purkinje fiber, the earliest and most pronounced alteration was a loss in overshoot resulting in a decrease in amplitude of the action potential. Shortly thereafter, the action potential duration shortened, and membrane resting potential decreased. In the ventricular muscle fiber, the earliest and most prominent change was a shortening of action potential duration. This was followed by loss in overshoot and decrease in amplitude of action potential. The membrane resting potential declined but was not significantly different from that noted in Purkinje fiber. The changes in both fibers were reversed completely by washing with Tyrode's solution. The earlier and more pronounced shortening of action potential duration in ventricular muscle fiber as compared to Purkinje is attributed to a greater need of the former for metabolic energy. It may also be conjectured that the greater shortening of action potential duration in ventricular fiber is due to a more marked inhibitory effect of K+ influx by 2,4 dinitrophenol in this fiber with the K+ influx coupled to metabolic energy. To account for the more enhanced loss in overshoot in Purkinje fiber, it is suggested that 2,4 dinitrophenol has a greater modifying effect on Purkinje fiber membrane or on its Na+ carrying system. This results in an earlier and more pronounced decrease in Na+ influx in this fiber as compared with ventricular muscle fiber.

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