Ouabain and Conduction Velocity at Different Heart Frequencies in Rabbit Auricles

IN the crista terminalis of isolated rabbit auricles we observed a relationship between the frequency of stimulation and the velocity of conduction, together with a relationship between the frequency of stimulation and the maximal rate of rise of the transmembrane action potential1. An increase in the frequency of stimulation causes an exponential decrease in both the maximal rate of rise and the velocity of conduction. The change in the velocity of conduction is most likely a direct result of the change in the maximal rate of rise2. An augmented intracellular sodium ion concentration caused by a relative insufficiency of the sodium–potassium pump might explain this phenomenon.