title: Enhanced type 1alpha metabotropic glutamate receptor-stimulated phosphoinositide signaling after pertussis toxin treatment.
abstract: The regulation of phosphoinositide hydrolysis by the type 1alpha metabotropic glutamate receptor (mGluR1alpha) was investigated in stably transfected baby hamster kidney (BHK) cells. Incubation of the cells with L-glutamate, quisqualate, and 1-aminocyclopentane-1S, 3R-dicarboxylic acid resulted in a marked accumulation of [3H]inositol monophosphate (InsP1) and inositol-1,4,5-trisphosphate [Ins(1,4,5)P3] mass in a time- and concentration-dependent manner. Pretreatment of BHK-mGluR1alpha cells with pertussis toxin [ 100 ng/ml, 24 hr] led to a dramatic 12-16-fold increase in the accumulation of [3H]InsP1 and a 2-fold increase in Ins(1,4,5)P3 in the absence of added agonist. Although only very low levels (</=1 microM) of L-glutamate could be detected in medium taken from control and PTX-treated cell monolayers, the PTX-elicited effect on basal [3H]InsP1 was fully reversed by preincubation of cells in the presence of glutamic-pyruvic transaminase and pyruvate, suggesting that an increased sensitivity to endogenous glutamate was responsible for the apparent agonist-independent activation of phosphoinositidase C (PIC) after PTX treatment. Consistent with this hypothesis, in the presence of glutamic-pyruvic transaminase/pyruvate, the maximal [3H]InsP1 response to quisqualate was increased by >/=75%, and the EC50 shifted leftward by 65-fold [-log EC50 values (molar), 7.26 +/- 0.23 versus 5.45 +/- 0.07; n = 4) in PTX-treated compared with control cells. In contrast, antagonist effects on agonist-stimulated [3H]InsP1 responses were similar in control and PTX-treated BHK-mGluR1alpha cells. These changes in the concentration-effect curves for mGluR agonists are consistent with a model in which the receptor associates with PTX-sensitive inhibitory (Gi/o) and PTX-insensitive stimulatory (Gq/11) G proteins that can each influence PIC activity. The present observations are consistent with a dual regulation of mGluR1alpha-mediated PIC activity that could be fundamental in controlling the output of phosphoinositide-derived messengers.
authors.affiliation: Department of Cell Physiology and Pharmacology, University of Leicester, University Road, Leicester LE1 9HN, UK.
authors.forename: A M
authors.initials: AM
authors.lastname: Carruthers
authors.forename: R A
authors.initials: RA
authors.lastname: Challiss
authors.forename: R
authors.initials: R
authors.lastname: Mistry
authors.forename: R
authors.initials: R
authors.lastname: Saunders
authors.forename: C
authors.initials: C
authors.lastname: Thomsen
authors.forename: S R
authors.initials: SR
authors.lastname: Nahorski
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D006224:Cricetinae; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism / Q000493:pharmacokinetics; D007295:Inositol Phosphates / Q000378:metabolism / Q000493:pharmacokinetics; D007668:Kidney / Q000378:metabolism / Q000648:ultrastructure; D007700:Kinetics; D008969:Molecular Sequence Data; D037342:Pertussis Toxin; D010716:Phosphatidylinositols / Q000378:metabolism / Q000493:pharmacokinetics / Q000502:physiology*; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism; D018094:Receptors, Metabotropic Glutamate / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology*; D013268:Stimulation, Chemical; D014316:Tritium; D014407:Tumor Cells, Cultured; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
chemical_list: D018690:Excitatory Amino Acid Agonists; D018691:Excitatory Amino Acid Antagonists; D007295:Inositol Phosphates; D010716:Phosphatidylinositols; D018094:Receptors, Metabotropic Glutamate; D010566:Virulence Factors, Bordetella; D014316:Tritium; C002647:inositol 1-phosphate; D018698:Glutamic Acid; D015544:Inositol 1,4,5-Trisphosphate; D037342:Pertussis Toxin; D010727:Phosphoric Diester Hydrolases; C021491:glycerophosphoinositol glycerophosphodiesterase; D019204:GTP-Binding Proteins