AJP - Heart and Circulatory Physiology, Vol 249, Issue 3 520-H533, Copyright © 1985 by American Physiological Society
Relationship between caffeine effects and calcium in canine cardiac Purkinje fibers
M. Di Gennaro and M. Vassalle
The actions of caffeine (1-9 mM) on electrical and mechanical events were
studied under conditions known to change the intracellular calcium in
canine cardiac Purkinje fibers perfused in vitro. It was found that
caffeine in a dose-dependent manner 1) shifts the early repolarization to
more positive values, 2) shifts the plateau to more negative values, 3)
prolongs the terminal phase 3 (induction of a "tail"), 4) transiently
increases and then decreases the force of contraction with respect to
control values, 5) causes a smaller tail in the presence of agents (local
anesthetics, tetrodotoxin, high potassium) that have been shown to diminish
the force of contraction, presumably by decreasing cellular calcium, 6)
causes the oscillatory potentials in high calcium to peak sooner after the
action potential and eventually to disappear as the tail develops, 7)
induces a tail at lower concentrations when cellular calcium is enhanced by
lowering the external sodium concentration or in the presence of
veratridine, and 8) fails to induce a marked tail in the presence of
metabolic inhibitors. It is concluded that in Purkinje fibers caffeine
induces a marked delay in the final repolarization through a process
modulated by calcium. This process may be related to an electrogenic
sodium-calcium exchange.
