Gettes L: Combined effects of rate, membrane potential and drugs on maximum rate of rise (Vmax) of action potential upstroke of guinea pig papillary muscle. Circ Res 38: 464

Abstract

SUMMARY We studied the effect of increasing the rate of stimu-lation on the maximum rate of rise of the action potential up-stroke (Vmax) in guinea pig papillary muscles at various resting membrane potentials and after the addition of quinidine and lidocaine to the perfusate. Increasing rate caused a decrease in Vma, due to interaction of three factors: (1) a metabolic factor, presumably re-setting of the Na-K pump, which caused a decrease in Vmai at all levels of resting potential between- 9 0 and- 6 0 mV, (2) a tran-sient decrease in resting potential which influenced Vma, when the resting potential was less negative than approximately- 8 0 mV, and (3) the recovery characteristics of Vma, which contributed to the decrease in this variable when rate was faster than 5/sec. As a result of these factors the steady state curve relating membrane potential to Vmai was itself rate-dependent. Lidocaine and quini-dine exaggerated the rate-dependent decrease in Vmox; however