AJP - Heart and Circulatory Physiology, Vol 249, Issue 6 1195-H1203, Copyright © 1985 by American Physiological Society
Effects of divalent cation ionophore A23187 on cardiac contractile parameters
J. J. Murray, J. G. Dobson Jr and P. W. Reed
The divalent cation ionophore A23187, when added to guinea pig papillary
muscle, produced contractile effects that were similar to those produced by
isoproterenol or histamine, but the ionophore's effects did not appear to
result from the release of endogenous transmitters or prostaglandin
production. Optimally effective concentrations of A23187 (6 microM) and
isoproterenol (1 microM) more than doubled the peak contractile force and
the rates of force development and relaxation and caused a 25% decrease in
the duration of the contraction. Both A23187 and isoproterenol decreased
the resting tension by approximately 0.15 g and significantly diminished
the magnitude of a potassium-induced contracture. The positive inotropic
effect of A23187 was prevented by incubating the tissue in calcium-depleted
medium and antagonized by D 600, a blocker of sarcolemmal calcium influx,
and acetylcholine. The contractile effects of A23187 appear to be related,
in part, to its ability to increase the movement of calcium across the
sarcolemma electroneutrally, since no change of the action potential
occurred. In addition, possible intracellular actions of this ionophore may
produce contractile effects that resemble those produced by isoproterenol
and that reflect an increased sequestration of calcium within the
myocardial cell.
