title: Regulation of glutamate carboxypeptidase II hydrolysis of N-acetylaspartylglutamate (NAAG) in crayfish nervous tissue is mediated by glial glutamate and acetylcholine receptors.
abstract: Glutamate carboxypeptidase II (GCPII), a glial ectoenzyme, is responsible for N-acetylaspartylglutamate (NAAG) hydrolysis. Its regulation in crayfish nervous tissue was investigated by examining uptake of [3H]glutamate derived from N-acetylaspartyl-[3H]glutamate ([3H]NAAG) to measure GCPII activity. Electrical stimulation (100 Hz, 10 min) during 30 min incubation with [3H]NAAG increased tissue [3H]glutamate tenfold. This was prevented by 2-(phosphonomethyl)-pentanedioic acid (2-PMPA), a GCPII inhibitor, suggesting that stimulation increased the hydrolysis of [3H]NAAG and metabolic recycling of [3H]glutamate. Antagonists of glial group II metabotropic glutamate receptors (mGLURII), NMDA receptors and acetylcholine (ACh) receptors that mediate axon-glia signaling in crayfish nerve fibers decreased the effect of stimulation by 58-83%, suggesting that glial receptor activation leads to stimulation of GCPII activity. In combination, they reduced [3H]NAAG hydrolysis during stimulation to unstimulated control levels. Agonist stimulation of mGLURII mimicked the effect of electrical stimulation, and was prevented by antagonists of GCPII or mGLURII. Raising extracellular K+ to three times the normal level stimulated [3H]NAAG release and GCPII activity. These effects were also blocked by antagonists of GCPII and mGLUR(II). No receptor antagonist or agonist tested or 2-PMPA affected uptake of [3H]glutamate. We conclude that NAAG released from stimulated nerve fibers activates its own hydrolysis via stimulation of GCPII activity mediated through glial mGLURII, NMDA and ACh receptors.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, Indiana, USA.
authors.forename: Albert K
authors.initials: AK
authors.lastname: Urazaev
authors.forename: Robert M
authors.initials: RM
authors.lastname: Grossfeld
authors.forename: Edward M
authors.initials: EM
authors.lastname: Lieberman
mesh_terms: D000818:Animals; D003400:Astacoidea; D004151:Dipeptides / Q000378:metabolism*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D043425:Glutamate Carboxypeptidase II / Q000378:metabolism*; D006868:Hydrolysis / Q000187:drug effects; D009457:Neuroglia / Q000187:drug effects / Q000378:metabolism*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D011950:Receptors, Cholinergic / Q000378:metabolism*; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*
chemical_list: D004151:Dipeptides; D018691:Excitatory Amino Acid Antagonists; D011950:Receptors, Cholinergic; D018094:Receptors, Metabotropic Glutamate; C108822:metabotropic glutamate receptor 2; C027172:isospaglumic acid; D043425:Glutamate Carboxypeptidase II