title: Oxytocin receptors differentially signal via Gq and Gi proteins in pregnant and nonpregnant rat uterine myocytes: implications for myometrial contractility.
abstract: Oxytocin (OT) receptors are important regulators of myometrial contractility. By using the activity of large conductance Ca2+-activated K+ (BKCa) channels as readout, we analyzed OT signaling in cells from nonpregnant (NPM) and pregnant (PM) rat myometrium in detail. In nystatin-perforated whole-cell patches from NPM cells, which leave the intracellular integrity intact, OT transiently increased BKCa-mediated outward currents (Iout). This OT-evoked Iout was caused by the Ca2+ transients in response to the Gq/11-mediated activation of phospholipase C and was inhibited by activation of protein kinase A (PKA). In an open-access whole-cell patch (OAP), the OT-induced transient rise in Iout was disrupted whereas the regulation of BKCa by the cAMP/PKA cascade remained intact. OT counteracted the isoprenaline, i.e. the beta-adrenoceptor/Gs-mediated effect in NPM cells measured in OAP. In contrast, OT further enhanced the beta-adrenoceptor/Gs-mediated effect on BKCa activity in PM cells. All OT effects in the OAP were mediated by pertussis toxin-sensitive Gi proteins and PKA. By quantitative real-time PCR and overexpression of the recombinant protein, we demonstrate that an up-regulation of the Gbetagamma-stimulated adenylyl cyclase II during pregnancy is most likely responsible for this switch. By studying the OT-evoked Iout in nystatin-perforated whole-cell patches of PM cells, we further detected that the OT receptor/Gibetagamma-mediated coactivation of adenylyl cyclase II enhanced the beta-adrenoceptor/Gs-induced suppression of the OT-evoked Ca2+ transients and thus diminishes and self-limits OT-induced contractility. The differential regulation of the PKA-mediated suppression of OT-evoked Ca2+ transients and BKCa activity likely supports uterine quiescence during pregnancy.
authors.affiliation: Institut für Pharmakologie für Pharmazeuten, Universitätsklinikum Hamburg-Eppendorf, Martinistrasse 52, D-20246 Hamburg, Germany.
authors.forename: Xiao-Bo
authors.initials: XB
authors.lastname: Zhou
authors.forename: Susanne
authors.initials: S
authors.lastname: Lutz
authors.forename: Frank
authors.initials: F
authors.lastname: Steffens
authors.forename: Michael
authors.initials: M
authors.lastname: Korth
authors.forename: Thomas
authors.initials: T
authors.lastname: Wieland
mesh_terms: D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D002478:Cells, Cultured; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism*; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism*; D006801:Humans; D008954:Models, Biological; D032389:Myocytes, Smooth Muscle / Q000378:metabolism*; D009215:Myometrium / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011247:Pregnancy; D051381:Rats; D017208:Rats, Wistar; D018045:Receptors, Oxytocin / Q000502:physiology*; D014590:Uterine Contraction / Q000378:metabolism / Q000502:physiology*
chemical_list: D015220:Calcium Channels; D018045:Receptors, Oxytocin; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11