Characterization of L-glutamate binding sites in rat spinal cord synaptic membranes: evidence for multiple chloride ion-dependent sites

• Published in: Journal of neurochemistry Vol. 47; no. 4; p. 1052
• Main Authors: Mena, E E, Pagnozzi, M J, Gullak, M F
• Format: Journal Article
• Language: English
• Published: England 01-10-1986
• Subjects: Aminobutyrates - pharmacology; Animals; Anions; Brain - metabolism; Calcium - pharmacology; Cations; Chlorides - pharmacology; Diencephalon - metabolism; Glutamates - metabolism; Glutamic Acid; Kinetics; Oxadiazoles - pharmacology; Quisqualic Acid; Rats; Receptors, Glutamate; Receptors, Neurotransmitter - drug effects; Receptors, Neurotransmitter - metabolism; Sodium - pharmacology; Spinal Cord - metabolism; Synaptic Membranes - metabolism; Telencephalon - metabolism
• ISSN: 0022-3042
• DOI: 10.1111/j.1471-4159.1986.tb00719.x

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).