Cellular resting and diastolic potentials in canine cardiac Purkinje cells: Effects of external [K +] and repetitive excitation

Abstract

Cellular potentials were measured in canine cardiac Purkinje fibers bathed in physiological solution in which the concentration of potassium, [K +] o, was varied systematically from 0.5 m m to 16 m m. Resting potentials, E C, were measured in quiescent preparations, and maximum diastolic potentials, E D, were measured in spontaneously-active preparations. In [K +] o of 1 m m and 2 m m, all preparations underwent spontaneous excitation; in [K +] o of 0.5 m m and 4 m m, some preparations were spontaneously active, and some were quiescent; in [K +] o of 8 m m and 16 m m, all preparations were quiescent. E c increased as [K +] o was reduced from 16 m m to 4 m m, but the potential increased along a slope less than and deviating continuously from that predicted by the Nernst equation for a K + electrode. E D increased as [K +] o was reduced from 4 m m to 2 m m, but it decreased again as [K +] o was reduced from 2 m m to 0.5 m m. All preparations subsequently were driven by repetitive stimuli for 5 min at a rate of 3.5 Hz, producing maximum hyperpolarization (increase of E D). Under these conditions, E D increased as [K +] o was reduced from 16 m m to 2 m m, along a slope closer to that predicted by the Nernst equation, yet diverging continuously. The potential decreased again as [K +] o was reduced from 2 m m to 0.5 m m. Possible explanations for the observed changes of potential with change of [K +] o from high levels to low levels include, according to conventional Membrane Theory, (i) the effects of other ionic gradients, (ii) inward-going rectification, and (iii) active transport of ions, and, according to the Association-Induction Hypothesis, relative reduction of the preferential surface adsorption of K + over Na +.