Intracellular K+ and Na+ activities under hypoxia, acidosis, and no glucose in dog hearts

Abstract

To gain a better understanding of the ionic mechanisms responsible for the electrophysiological disturbances occurring during myocardial ischemia, transmembrane potentials and intracellular potassium (aiK) and sodium (aiNa) ion activities were measured under individual and combined conditions of hypoxia (Po2 less than 50 mmHg), respiratory acidosis (pH 6.6), and no glucose in isolated epicardial ventricular muscle preparations of the canine heart using conventional and ion-selective microelectrode techniques. After 30 min superfusion with hypoxic, acidic, and glucose-free solution under 2-Hz stimulation, resting membrane potential (RMP) was significantly reduced from -85.5 +/- 0.6 to -69.5 +/- 1.0 mV, accompanied by decreases in action potential amplitude, maximum upstroke velocity of phase O, and action potential duration. aiK was significantly decreased from 101.0 +/- 5.6 to 79.5 +/- 5.8 mM, whereas aiNa was not significantly altered by the combined condition. RMP and aiK were moderately decreased by hypoxia alone, slightly decreased by acidosis, and hardly affected by the glucose-free condition. The extent of depolarization was well correlated with the decrease in aiK. These results suggest that Na+-K+ pump inhibition may not be a major cause of K+ efflux from myocardial cells under the hypoxic, acidic, and glucose-free condition and that hypoxia is the most important factor affecting aiK and RMP among these conditions.