TRPC1, STIM1, and ORAI Influence Signal-Regulated Intracellular and Endoplasmic Reticulum Calcium Dynamics in Human Myometrial Cells

To explore the relationship between signal-stimulated increases in intracellular calcium ([Ca2+](i)) and depletion and refilling of the endoplasmic reticulum (ER) Ca2+ stores ([Ca2+](L)) in human myometrial cells, we measured simultaneous changes in [Ca2+](i) and [Ca2+](L) using Fura-2 and Mag-fluo-4, respectively, in PHM1-41 immortalized and primary cells derived from pregnant myometrium and in primary cells derived from nonpregnant tissue. Signal-and extracellular Ca2+-dependent increases in [Ca2+](i) (SRCE) and ER refilling stimulated by oxytocin and cyclopiazonic acid were not inhibited by voltage-operated channel blocker nifedipine or mibefradil, inhibition of Na+/Ca2+ exchange with KB-R7943, or zero extracellular Na+ in PHM1-41 cells. Gadolinium-inhibited oxytocin-and cyclopiazonic acid-induced SRCE and slowed ER store refilling. TRPC1 mRNA knockdown specifically inhibited oxytocin-stimulated SRCE but had no statistically significant effect on ER store refilling and no effect on either parameter following cyclopiazonic acid treatment. Dominant negative STIM Delta ERM expression attenuated oxytocin-and thapsigargin-stimulated SRCE. Both STIM1 and ORAI1-ORAI3 mRNA knockdowns significantly attenuated oxytocin- and cyclopiazonic acid-stimulated SRCE. The data also suggest that reduction in STIM1 or ORAI1-ORAI3 mRNA can impede the rate of ER store refilling following removal of SERCA inhibition. These data provide evidence for both distinct and overlapping influences of TRPC1, STIM1, and ORAI1-ORAI3 on SRCE and ER store refilling in human myometrial cells that may contribute to the regulation of myometrial Ca2+ dynamics. These findings have important implications for understanding the control of myometrial Ca2+ dynamics in relation to myometrial contractile function.