AJP - Endocrinology and Metabolism, Vol 269, Issue 4 E779-E785, Copyright © 1995 by American Physiological Society
Ionomycin-stimulated phasic myometrial contractions
M. Phillippe, E. M. Chien, M. Freij and T. Saunders
Department of Obstetrics and Gynecology, University of Chicago, Illinois 60637, USA.
Ionomycin, a calcium ionophore, facilitates the sustained entry of
extracellular calcium; however, in myometrial tissue it stimulates phasic
contractions. This study sought to define further 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 on 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.
