High extracellular sodium and digoxin-induced arrhythmias in guinea-pig ventricular myocardium

Abstract

Oscillatory fluctuations in diastolic potential [ 4, 10] and triggered rhythmical activity [ 4] are well known manifestations of digitalis intoxication and are attributed to intracellular Ca 2+ overload consecutive to an elevated intracellular Na + [ 7]. In the present paper we report the electrophysiological effects of elevated extracellular Na + on the spontaneous rhythmical activity and oscillatory fluctuations in digoxin-intoxicated ventricular cells. Our results show that by increasing extracellular Na + from 135 m m to 175 m m, we were able to abolish spontaneous rhythmical activity but were not able to suppress the damped sinusoidal oscillations in the resting membrane potential. We suggest that Na +Ca 2+ exchange would be stimulated by a greater Na + gradient, resulting in an enhanced Ca 2+ extrusion.