Effects of Low and High Concentrations of Potassium on the Simultaneously Recorded Purkinje and Ventricular Action Potentials of the Perfused Pig Moderator Band

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Abstract
The use of the perfused pig moderator band has allowed us to study the rapid simultaneous changes in Purkinje and ventricular action potentials induced by perfusing solutions of high (10 to 12 mM) and low (0.6 to 0.8 mM) K concentrations. High K shortened the plateau more in Purkinje fibers than in ventricular fibers and decreased the difference between the action potential durations of the two fiber types. Low K prolonged the plateau in Purkinje fibers but shortened it in ventricular fibers and increased the difference between the action potential durations. Low K initially hyperpolarized both Purkinje and ventricular fibers. However, the resting potential of the Purkinje fiber subsequently decreased as phase-4 depolarization increased. The decreased maximum repolarization potential associated with low K-induced pacemaker activity was time rather than voltage dependent. When the perfusate was changed from low K to control (K = 4.8 mM), phase-4 depolarization was rapidly suppressed and the action potential of the Purkinje fiber was shortened to less than that produced by high K, and then changes in amplitude of the resting and action potentials occurred. Our observations help to explain some of the effects of low and high K on rhythm and conduction.