AJP - Heart and Circulatory Physiology, Vol 241, Issue 4 646-H653, Copyright © 1981 by American Physiological Society
Voltage dependence of digitalis afterpotentials, aftercontractions, and inotropy
J. A. Wasserstrom and G. R. Ferrier
The effects of membrane potential on digitalis-induced oscillatory
afterpotentials (OAP) and aftercontractions (AC) were investigated in
isolated canine false tendons and canine and feline papillary muscles.
Transmembrane potential and contractions were measured simultaneously.
Membrane potential was varied by current applied through an extracellular
pipet. The amplitudes of OAP and AC induced by acetylstrophanthidin
(0.5-1.0 X 10(-7) g/ml) or actodigin (0.5-1.0 X 10(-6) g/ml) were increased
by depolarization and decreased or abolished by hyperpolarization in all
tissues. Prior to the appearance of OAP and AC in preparations exposed to
the drugs, depolarization caused both phenomena to appear. As in muscle,
the strength of beats superimposed on the ascending limb of AC was
potentiated, and the strength of beats superimposed on the relaxation phase
was depotentiated. When the amplitude of AC was decreased by
hyperpolarization, both potentiation and depotentiation were diminished.
This effect was accompanied by a partial reversal of the changes induced by
acetylstrophanthidin in the course of restitution of contractility and the
configuration of the force-frequency relation.
