title: Estrogen regulation of the dopamine-activated GIRK channel in pituitary lactotrophs: implications for regulation of prolactin release during the estrous cycle.
abstract: Prolactin (PRL), synthesized and secreted from lactotrophs of the anterior pituitary gland, is tonically inhibited by hypothalamic dopamine (DA) throughout the female reproductive (estrous) cycle. Our laboratory has shown that DA hyperpolarizes these cells by activating G protein-coupled inwardly rectifying K(+) (GIRK) channels; however, this response is only observed on proestrus. While the cellular mechanisms that allow for functional expression of this unique DA-signaling pathway are unclear, we hypothesized that activation of the DA-GIRK effector pathway is due to the rise in circulating estrogen (E₂) during the preceding day of diestrus. Thus, we examined the effects of E₂ on primary lactotrophs isolated from female rats. Treatment with a physiological concentration of E₂ (40-80 pg/ml, in vivo or in vitro) induced a proestrous phenotype in diestrous lactotrophs. These cells exhibited a DA-induced membrane hyperpolarization, as well as a secretory rebound of PRL following DA withdrawal (characteristic of proestrous cells). Internal dialysis of GTPγS demonstrated that E₂ exposure enabled functional expression of GIRK channels, and this regulation by E₂ did not involve the D₂R. The effect of E₂ was blocked by the receptor antagonist, ICI 182,780, and by the protein synthesis inhibitor, cycloheximide. Single-cell analysis revealed increased mRNA expression of GIRK channel subunits in E₂-treated lactotrophs. While E₂ is known to have multiple actions on the lactotroph, the present findings illuminate a novel action of E₂ in lactotrophs-regulation of the expression of a DA effector, the GIRK channel.
authors.affiliation: James L. Winkle College of Pharmacy, University of Cincinnati, Cincinnati, Ohio, USA. karen.gregerson@uc.edu
authors.forename: Heather R
authors.initials: HR
authors.lastname: Christensen
authors.forename: Qinghua
authors.initials: Q
authors.lastname: Zeng
authors.forename: Michael K
authors.initials: MK
authors.lastname: Murawsky
authors.forename: Karen A
authors.initials: KA
authors.lastname: Gregerson
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003956:Dialysis; D004298:Dopamine / Q000378:metabolism*; D004343:Drug Implants; D004958:Estradiol / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000008:administration & dosage; D030762:Estrous Cycle / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D000077267:Fulvestrant; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000008:administration & dosage; D052682:Lactotrophs / Q000187:drug effects / Q000378:metabolism*; D008564:Membrane Potentials; D010052:Ovariectomy; D010641:Phenotype; D024661:Potassium Channels, Inwardly Rectifying / Q000378:metabolism; D011388:Prolactin / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000008:administration & dosage; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017448:Receptors, Dopamine D2 / Q000378:metabolism; D013997:Time Factors
chemical_list: D004343:Drug Implants; D004965:Estrogen Antagonists; D051676:G Protein-Coupled Inwardly-Rectifying Potassium Channels; C092387:Kcnj5 protein, rat; C497070:Kcnj6 protein, rat; D024661:Potassium Channels, Inwardly Rectifying; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D017448:Receptors, Dopamine D2; D000077267:Fulvestrant; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004958:Estradiol; D011388:Prolactin; D003513:Cycloheximide; D004298:Dopamine