Parachloromercuribenzoate on action potentials of Purkinje and ventricular fibers of hog heart

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Abstract
Parachloromercuribenzoate (0.5 to 2.6 x 10–4 m) was administered to a hog Purkinje fiber ventricular muscle preparation and its effects on transmembrane action potentials of the two types of fibers were studied. Parachloromercuribenzoate produced changes in action potential of Purkinje but little change in that of ventricular fiber. The earliest alteration in Purkinje fiber was a decrease in overshoot. This was followed by a decrease in height of action potential and slowing in rate of depolarization. There was a decline in diastolic resting potential but this occurred late. The difference in response of the two types of fibers is not readily explainable. One possible difference is that the sulfhydryl groups in Purkinje fiber may be more available for binding with p-chloromercuribenzoate. Another hypothesis is predicated on differences in metabolism in two types of fibers. There is evidence to indicate that Purkinje fiber utilizes anaerobic glycolysis predominantly. A greater sensitivity of the glycolytic-dependent sulfhydryl enzymes to action of this agent would interfere with metabolism in Purkinje fiber and cause a decrease in its resting potential.