G protein-coupled estrogen receptor 1-mediated effects in the rat myometrium

Tica AA, Dun EC, Tica OS, Gao X, Arterburn JB, Brailoiu GC, Oprea TI, Brailoiu E. G protein-coupled estrogen receptor 1-mediated effects in the rat myometrium. Am J Physiol Cell Physiol 301: C1262-C1269, 2011. First published August 24, 2011; doi: 10.1152/ajpcell.00501.2010.-G protein-coupled estrogen receptor 1 (GPER), also named GPR30, has been previously identified in the female reproductive system. In this study, GPER expression was found in the female rat myometrium by reverse transcriptase-polymerase chain reaction and immunocytochemistry. Using GPER-selective ligands, we assessed the effects of the GPER activation on resting membrane potential and cytosolic Ca2+ concentration ([Ca2+](i)) in rat myometrial cells, as well as on contractility of rat uterine strips. G-1, a specific GPER agonist, induced a concentration-dependent depolarization and increase in [Ca2+](i) in myometrial cells. The depolarization was abolished in Na+-free saline. G-1-induced [Ca2+](i) increase was markedly decreased by nifedipine, a L-type Ca2+ channel blocker, by Ca2+-free or Na+-free saline. Intracellular administration of G-1 produced a faster and transitory increase in [Ca2+](i), with a higher amplitude than that induced by extracellular application, supporting an intracellular localization of the functional GPER in myometrial cells. Depletion of internal Ca2+ stores with thapsigargin produced a robust store-activated Ca2+ entry; the Ca2+ response to G-1 was similar to the constitutive Ca2+ entry and did not seem to involve store-operated Ca2+ entry. In rat uterine strips, administration of G-1 increased the frequency and amplitude of contractions and the area under the contractility curve. The effects of G-1 on membrane potential, [Ca2+](i), and uterine contractility were prevented by pretreatment with G-15, a GPER antagonist, further supporting the involvement of GPER in these responses. Taken together, our results indicate that GPER is expressed and functional in rat myometrium. GPER activation produces depolarization, elevates [Ca2+](i) and increases contractility in myometrial cells.