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

Oscillatory fluctuations in diastolic potential [4, 10] and triggered rhythmical activity [4] are well known manifestations of digitalis intoxication and are attributed to intracellular Ca2+ 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 mM to 175 mM, 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+-Ca2+ exchange would be stimulated by a greater Na+ gradient, resulting in an enhanced Ca2+ extrusion.