title: Impaired G protein function in gallbladder muscle from progesterone-treated guinea pigs.
abstract: This study was designed to elucidate the mechanism of action of progesterone on gallbladder smooth muscle in guinea pigs. Adult male guinea pigs were treated with either progesterone (2 mg.kg-1.day-1) or saline for 7 days. Gallbladder muscle cells were isolated by enzymatic digestion with collagenase. Contractile responses to agonists were expressed as percent shortening from control cell length. [35S]guanosine 5'-O-(3-thiotriphosphate) ([35S]GTP gamma S)-binding properties of G proteins were assessed in crude membranes of gallbladder muscle with or without cholecystokinin octapeptide (CCK-8) stimulation. Gallbladder muscle cells from progesterone-treated guinea pigs exhibited an impaired contractile response to CCK-8, GTP gamma S, or aluminum fluoride but a normal response to potassium chloride or D-myo-inositol 1,4,5-trisphosphate compared with controls. Western blot analysis of gallbladder muscle revealed the presence of Gi1-2, Gi3, Gq/11, and Gs proteins. The maximal contraction induced by CCK-8 was blocked by pertussis toxin and Gi alpha 3-specific antibodies, but not by Gi alpha 1-2 or Gq/11 alpha antibodies. CCK-8 caused a significant increase in [35S]GTP gamma S binding to Gi alpha 3, but not to Gq/11 alpha or Gi alpha 1-2. The stimulation of Gi alpha 3 binding, however, was significantly reduced in gallbladder muscle membranes from progesterone-treated guinea pigs compared with that in control animals. In conclusion, progesterone might cause gallbladder hypomotility by downregulating Gi3 proteins.
authors.affiliation: Department of Medicine, Rhode Island Hospital, Providence, USA.
authors.forename: Q
authors.initials: Q
authors.lastname: Chen
authors.forename: V
authors.initials: V
authors.lastname: Chitinavis
authors.forename: Z
authors.initials: Z
authors.lastname: Xiao
authors.forename: P
authors.initials: P
authors.lastname: Yu
authors.forename: S
authors.initials: S
authors.lastname: Oh
authors.forename: P
authors.initials: P
authors.lastname: Biancani
authors.forename: J
authors.initials: J
authors.lastname: Behar
mesh_terms: D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D002766:Cholecystokinin / Q000502:physiology; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology*; D005704:Gallbladder / Q000502:physiology*; D006168:Guinea Pigs; D015544:Inositol 1,4,5-Trisphosphate / Q000494:pharmacology; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D037342:Pertussis Toxin; D011374:Progesterone / Q000494:pharmacology / Q000502:physiology*; D015398:Signal Transduction; D012844:Sincalide / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
chemical_list: D017607:Aluminum Compounds; D010566:Virulence Factors, Bordetella; D011374:Progesterone; D015544:Inositol 1,4,5-Trisphosphate; D002766:Cholecystokinin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D012844:Sincalide; D005459:Fluorides; C032311:aluminum fluoride