Tyrosine kinase-mediated activation of cytosolic calcium oscillations and phasic myometrial contractions

These studies sought to test the hypothesis that tyrosine kinase-stimulated phasic myometrial contractions are mediated by activation of the phosphatidylinositol (PI)-signaling pathway and the generation of cytosolic calcium oscillations. For these studies, uterine tissue was obtained from adult female Sprague-Dawley white rats during the proestrus/estrus phase of the cycle. In vitro contraction studies were performed using pervanadate (a tyrosine phosphatase inhibitor) with and without inhibitors of the PI-signaling pathway, including 2-nitro-4-carboxyphenyl-N,N-diphenylcarbamate (a phospholipase C inhibitor), thimerosal (an inositol-trisphosphate receptor/channel inhibitor), and Ruthenium red (a ryanodine receptor inhibitor), and with oxytocin or prostaglandin F2 alpha (two classic uterotonic agonists). Cytosolic calcium studies were performed using Fura-2-loaded myometrial strips. During these studies, pervanadate was observed to produce cytosolic calcium oscillations and phasic contractions in myometrial tissue comparable to those produced in response to oxytocin and prostaglandin F2 alpha. The pervanadate-stimulated phasic contractions were significantly suppressed in response to inhibition of phospholipase C, the inositol-trisphosphate receptor, and the ryanodine receptor, thereby confirming the importance of the PI-signaling pathway during tyrosine kinase-associated myometrial activity. Further confirming the important and shared role for the PI-signaling pathway during pervanadate-stimulated myometrial contractions, no significant additive effects were observed when classic uterotonic agonists such as oxytocin or prostaglandin F2 alpha were combined with pervanadate.