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Characterization of L‐Glutamate Binding Sites in Rat Spinal Cord Synaptic Membranes: Evidence for Multiple Chloride Ion‐Dependent Sites
Author(s) -
Mena E. Edward,
Pagnozzi Martin J.,
Gullak Mary F.
Publication year - 1986
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1986.tb00719.x
Subject(s) - forebrain , quisqualic acid , spinal cord , membrane , binding site , chemistry , glutamate receptor , biophysics , medicine , biochemistry , endocrinology , central nervous system , biology , neuroscience , kainic acid , receptor
The effects of various ions on L‐glutamate (L‐Glu) binding sites (Na + ‐dependent, Cl − ‐dependent, and CP − ‐independent) in synaptic plasma membranes (SPM) isolated from rat spinal cord and forebrain were examined. CP − ‐de‐pendent binding sites were over twofold higher in spinal cord ( B max = 152 ± 34 pmol/mg protein) as compared to forebrain SPM ( B max = 64 ± 12 pmol/mg protein). Na + dependent binding, on the other hand, was nearly sixfold less in spinal cord ( B max = 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 ( V max of 2.89 and 22.3 pmol/mg protein/min, respectively). The effects of Na + , K + , NH 4 + , and Ca 2+ on L‐Glu binding sites were similar in both regions of the CNS. In addition, in spinal cord membranes, Br − , I − , and NO 3 − were equivalent to C − in their capacity to stimulate L‐Glu binding, whereas F − and CO 3 2− 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., K i values of 5.7 ± 1.4 μM and 119 ± 38 n M for 2‐amino‐4‐phosphonobutyric acid (AP4) and quisqualic acid, (QUIS), respectively]. The other CP‐dependent site was unaffected by AP4 but was blocked by QUIS (K i = 14.2 ± 4.8 μM ).