Interaction of guanine nucleotides with [3H]kainate and 6-[3H]cyano-7-nitroquinoxaline-2,3-dione binding in goldfish brain.
Recent reports have suggested that a major proportion of [3H]kainate binding in goldfish brain is to a novel form of G-protein-linked glutamate receptor. Here we confirm that guanine nucleotides decrease [3H]kainate binding in goldfish brain membranes, but that binding is also reduced to a similar extent under conditions where G-protein modulation should be minimised. Inclusion of GTP gamma S resulted in an approximately twofold decrease in the affinity of [3H]kainate binding and a 50% reduction in the apparent Bmax values in both Mg2+/Na+ and Mg2+/Na(+)-free buffer when assayed at 0 degrees C. The pharmacology of [3H]kainate binding is similar to that of well-characterised ionotropic kainate receptors but unlike that of known metabotropic glutamate receptors, with neither 1S,3R-amino-1,3-cyclopentanedicarboxylic acid (1S,3R-ACPD) nor ibotenic acid being effective competitors. The molecular mass of the [3H]kainate binding protein, as determined by radiation inactivation, was 40 kDa, similar to the subunit sizes of other lower vertebrate kainate binding proteins that are believed to comprise ligand-gated ion channels. Furthermore, GTP gamma S also inhibited the binding of the non-NMDA receptor-selective antagonist 6-[3H]cyano-7-nitroquinoxaline-2,3-dione. These data strongly suggest that the regulatory interaction between guanine nucleotides and [3H]kainate and 6-[3H]cyano-7-nitroquinoxaline-2,3-dione binding is complex and involves competition at the agonist/antagonist binding site in addition to any G-protein-mediated modulation.
Barnes
J M
JM
Department of Pharmacology, Medical School, University of Birmingham, England.
Murphy
P A
PA
Kirkham
D
D
Henley
J M
JM
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000227:Adenine Nucleotides / Q000494:pharmacology*; D000818:Animals; D001345:Autoradiography; D001665:Binding Sites; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006054:Goldfish; D006150:Guanine Nucleotides / Q000494:pharmacology*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D007608:Kainic Acid / Q000378:metabolism*; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D011810:Quinoxalines / Q000378:metabolism*; D011869:Radioligand Assay; D018092:Kainic Acid Receptors / Q000187:drug effects / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D014316:Tritium
D018750:6-Cyano-7-nitroquinoxaline-2,3-dione; D000227:Adenine Nucleotides; D006150:Guanine Nucleotides; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D007608:Kainic Acid; D008274:Magnesium; D011810:Quinoxalines; D018092:Kainic Acid Receptors; D012964:Sodium; D014316:Tritium