title: N-methyl-D-aspartate-evoked adenosine and inosine release from neurons requires extracellular calcium.
abstract: The nucleoside adenosine (ADO) is a neuromodulator in brain. ADO and its metabolite inosine (INO) have been shown to increase cell viability in stroke models. During ischemia, extracellular levels of both ADO and INO are increased. In this study, we treated rat cortical neurons with N-methyl-D-aspartate (NMDA) to initiate excitotoxicity and then investigated the mechanisms of ADO and INO release. NMDA induced a significant increase in ADO and INO production. The effect of NMDA receptor antagonists on NMDA-evoked ADO and INO release was examined. MK-801 (1 micromol/L), a potent antagonist that lacks receptor subunit selectivity, completely blocked evoked release of both ADO and INO. Memantine (10 micromol/L), a lower affinity antagonist that also lacks subunit selectivity, blocked INO, but not ADO, release. Ifenprodil (10 micromol/L), an inhibitor selective for NMDA receptors containing the NR2B subunit, completely blocked evoked ADO and INO release. NVP-AAM077 (NVP, 0.4 micromol/L), an inhibitor selective for NMDA receptors containing the NR2A subunit, did not significantly block evoked release of either ADO or INO. Removal of extracellular Ca2+ abolished NMDA-evoked release of both ADO and INO. BAPTA (25 micromol/L), which chelates intracellular Ca2+, had no significant effect on either ADO or INO release unless extracellular Ca2+ was also removed. Inhibitors of Ca2+/calmodulin-dependent protein kinase II (CaMKII) prevented NMDA-evoked ADO and INO release and decreased nucleoside transporter function. These data indicate that NMDA-evoked ADO and INO release is dependent on subunit composition of NMDA receptors. As well, NMDA-evoked ADO and INO release requires nucleoside transporters and extracellular Ca2+ and is enhanced by activation of CaMKII.
authors.affiliation: Department of Pharmacology and Therapeutics, A402-753 McDermot Avenue, University of Manitoba, Winnipeg, MB R3E 0T6, Canada.
authors.forename: Christina R
authors.initials: CR
authors.lastname: Zamzow
authors.forename: Ratna
authors.initials: R
authors.lastname: Bose
authors.forename: Fiona E
authors.initials: FE
authors.lastname: Parkinson
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000502:physiology; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology; D007288:Inosine / Q000378:metabolism*; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D010880:Piperidines / Q000494:pharmacology; D011687:Purines / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000502:physiology
chemical_list: C498554:5-(alpha-methyl-4-bromobenzylamino)phosphonomethyl-1,4-dihydroquinoxaline-2,3-dione; D002614:Chelating Agents; D018691:Excitatory Amino Acid Antagonists; C120997:NR2A NMDA receptor; C121001:NR2B NMDA receptor; D010880:Piperidines; D011687:Purines; D011810:Quinoxalines; D016194:Receptors, N-Methyl-D-Aspartate; D004533:Egtazic Acid; D007288:Inosine; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D000241:Adenosine; C010739:ifenprodil; D002118:Calcium