AJP - Cell Physiology, Vol 235, Issue 1 13-C19, Copyright © 1978 by American Physiological Society
Calcium fluxes and contractility in isolated guinea pig atrium: effect of A23187
D. R. Holland, W. M. Armstrong and M. I. Steinberg
The Ca2+ ionophore A23187 (10(-6) to 3 X 10(-5) M) increased the force of
contraction is isolated guinea pig atria. In individual twitches, peak
tension, maximum rate of tension development, time to peak tension, and
total twitch duration were all increased by A23187. Tripelennamine,
indomethacin, and atropine did not significantly alter the inotropic effect
of A23187. Serotonin produced changes in individual twitches that differed
qualitatively and quantitatively from those of A23187. Therefore, the
inotropic action of A23187 is probably not mediated by release of
endogenous histamine, prostaglandins, acetylcholine, or serotonin. 45Ca
influx and efflux were increased by A23187. The enhanced 45Ca efflux
exceeded that which would be predicted if the ionophore acted only to
increase the passive Ca2+ permeability of the myocardial cell membrane.
These results suggest that A23187 facilitates the entry of extracellular
Ca2+ into the myocardial cell and the release of intracellular Ca2+ stores
into the myoplasm. The resultant increase in intracellular Ca2+ activity
could account for the positive inotropic action of A23187.
