Ionomycin-stimulated phasic myometrial contractions.
Phillippe, Mark, Edward M Chien, Maysoun Freij, Trevania Saunders.
Department of Obstetrics & Gynecology, University of Chicago,
Chicago, Illinois
APStracts 2:0120E, 1995.
Ionomycin, a calcium ionophore, facilitates the sustained entry of
extracellular calcium; however, in myometrial tissue it stimulates
phasic contractions. This study sought to further define this
unanticipated effect of ionomycin, and to begin to explore the
possible mechanism(s) involved. Utilizing rat uterine strips, in
vitro isometric contraction studies were performed to determine the
effects of ionomycin with and without membrane-permeant inhibitors of
cytosolic calcium oscillations. To determine the effects of ionomycin
on phospholipase C, qualitative inositol-phosphate production studies
were performed. The in vitro contraction studies confirmed that
ionomycin-stimulated phasic myometrial contractions were potentially
dependent upon stimulation of phospholipase C, calcium-induced
calcium release, and additional calcium influx through
dihydropyridine-sensitive membrane calcium channels. The inositol
phosphate production studies confirmed that ionomycin stimulated
phospholipase C in a dose-related fashion to levels comparable to
oxytocin. In summary, these observations have confirmed the ability
of ionomycin to generate dose-related phasic myometrial contractions
through mechanisms potentially involving the phosphatidylinositol
signaling pathway.
Received 31 August 1994; accepted in final form 12 May 1995.
APS Manuscript Number E354-4.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 May 1995.