Characterization of L-glutamate binding sites in rat spinal cord synaptic membranes: evidence for multiple chloride ion-dependent sites.
The effects of various ions on L-glutamate (L-Glu) binding sites (Na+-dependent, Cl(-)-dependent, and Cl(-)-independent) in synaptic plasma membranes (SPM) isolated from rat spinal cord and forebrain were examined. Cl(-)-dependent binding sites were over twofold higher in spinal cord (Bmax = 152 +/- 34 pmol/mg protein) as compared to forebrain SPM (Bmax = 64 +/- 12 pmol/mg protein). Na+-dependent binding, on the other hand, was nearly sixfold less in spinal cord (Bmax = 74 +/- 10 pmol/mg protein) compared to forebrain SPM (408 +/- 26 pmol/mg protein). Uptake of L-Glu (Na+-dependent) was also eightfold less in the P2 fraction from spinal cord relative to forebrain (Vmax of 2.89 and 22.3 pmol/mg protein/min, respectively). The effects of Na+, K+, NH4+, and Ca2+ on L-Glu binding sites were similar in both regions of the CNS. In addition, in spinal cord membranes, Br-, I-, and NO3- were equivalent to Cl- in their capacity to stimulate L-Glu binding, whereas F- and CO3- were less effective. Cl(-)-dependent L-Glu binding in spinal cord membranes consisted of two distinct sites. The predominant site (74% of the total) had characteristics similar to the Cl(-)-dependent binding site in forebrain membranes [i.e., Ki values of 5.7 +/- 1.4 microM and 119 +/- 38 nM for 2-amino-4-phosphonobutyric acid (AP4) and quisqualic acid, (QUIS), respectively]. The other Cl(-)-dependent site was unaffected by AP4 but was blocked by QUIS (Ki = 14.2 +/- 4.8 microM).
D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D000838:Anions; D001921:Brain / Q000378:metabolism*; D002118:Calcium / Q000494:pharmacology; D002412:Cations; D002712:Chlorides / Q000494:pharmacology*; D004027:Diencephalon / Q000378:metabolism; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D007700:Kinetics; D010069:Oxadiazoles / Q000494:pharmacology; D016318:Quisqualic Acid; D051381:Rats; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D013116:Spinal Cord / Q000378:metabolism*; D013570:Synaptic Membranes / Q000378:metabolism*; D013687:Telencephalon / Q000378:metabolism
D000613:Aminobutyrates; D000838:Anions; D002412:Cations; D002712:Chlorides; D005971:Glutamates; D010069:Oxadiazoles; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D018698:Glutamic Acid; D016318:Quisqualic Acid; D012964:Sodium; C012729:2-amino-4-phosphonobutyric acid; D002118:Calcium