Mobilization of calcium by the brief application of oxytocin and prostaglandin E2 in single cultured human myometrial cells

Abstract

Intracellular calcium ([Ca2+]i) mobilization was studied in single cultured human myometrial cells in response to the agonists oxytocin and prostaglandin E2 (PGE2) using the fluorescent dye Fura‐2. Oxytocin and PGE2 applications were associated with an increase in [Ca2+]i, although there was a marked intercell variation in the amplitude of the agonist‐induced response. Removal of extracellular calcium ([Ca2+]o) reduced the oxytocin‐induced rise and abolished the PGE2‐induced rise in [Ca2+]i, thereby demonstrating that oxytocin but not PGE2 can mobilize intracellular stores of calcium. In nominally calcium‐free medium, [Ca2+]i was not increased by PGE2 but subsequent application of oxytocin increased [Ca2+]i, thereby demonstrating that, within a single cell, calcium stores were mobilized by oxytocin and not PGE2. The intracellular calcium stores were completely depleted by a single application of oxytocin and not replenished in the absence of [Ca2+]o. Perfusion with calcium‐containing medium for 100 s enabled store refilling. Cell depolarization by 140 mM‐K+ caused a transient increase followed by a sustained elevation of [Ca2+]i on which were superimposed small fluctuations. Oxytocin caused an influx of calcium in cells depolarized by K+. This was more marked than that obtained with PGE2. © 1992 The Physiological Society