Epidermal growth factor increases phosphoinositide turnover and intracellular free calcium in an immortalized human myometrial cell line independent of the arachidonic acid metabolic pathway.

Abstract

The objectives of this study were to determine whether epidermal growth factor increases intracellular calcium and phosphoinositide turnover in human myometrial cells by a tyrosine kinase-mediated mechanism, to evaluate an obligatory role for arachidonic acid metabolites in these actions, and to compare the actions of epidermal growth factor and oxytocin. Intracellular calcium and phosphoinositide turnover were measured in a myometrial cell line after stimulation with epidermal growth factor (0.1 to 100 nmol/L) or oxytocin (20 nmol/L). The effects of nifedipine, thapsigargin, genestein and tyrphostin, the guanosine triphosphate binding protein antagonist GPA-7, indomethacin, and nordihydroguaiaretic acid were determined. Data were analyzed by analysis of variance and Duncan's multiple-range test. Epidermal growth factor stimulated phosphoinositide turnover and increased intracellular calcium in a dose-dependent manner (median effective concentration 2.6 nmol/L). In contrast to oxytocin, the effects of epidermal growth factor were inhibited by tyrosine kinase inhibitors but not by GPA-7. Indomethacin and nordihydroguaiaretic acid did not inhibit the epidermal growth factor-stimulated increase in intracellular calcium. The acute epidermal growth factor-stimulated increase in intracellular calcium in this myometrial cell line is primarily derived from release of calcium from intracellular stores, and it involves the activation of a tyrosine kinase, presumably the epidermal growth factor receptor. Arachidonic acid metabolites are not obligatory intermediates. Oxytocin increases phosphoinositide turnover and intracellular calcium by a distinctly different pathway.