Ionic regulation of glutamate binding sites.
Cl- and Ca2+ increase glutamate binding to rat synaptic plasma membranes (SPMs) by revealing a distinct class of L-glutamate (L-Glu) binding sites. The present study was conducted to examine both the anion specificity of this response and the nature of the interaction between Cl- and Ca2+. Of the anions tested, Br- was the most effective in increasing the levels of L-Glu binding. Other effective anions were Cl-, NO3- and formate while F-, HCO3-CIO4-, propionate, SO42- and PO43- were ineffective. The anion specificity was similar to that observed for the Cl- membrane channel, suggesting that this binding site and the ion channel may be related. In the absence of Cl-, Ca2+ has little effect on L-Glu binding. Increasing the Cl- concentration increased the apparent affinity (decreased KCa2+) of the Ca2+-stimulated, L-Glu binding component and also increased the maximal amount of the enhancement. Conversely, increasing Ca2+ levels increased the maximal enhancement of L-Glu binding brought about by Cl- without affecting the KCl- of the effect. Prior incubation of membranes with Ca2+ did not raise the level of L-Glu binding. Furthermore, EGTA was able to reverse the stimulation of L-Glu binding due to Ca2+. The results indicate that Ca2+ acts ionically to enhance L-Glu binding to rat SPMs.
D000818:Animals; D000838:Anions / Q000494:pharmacology; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology*; D002712:Chlorides / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D007700:Kinetics; D051381:Rats; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism*
D000838:Anions; D002712:Chlorides; D005971:Glutamates; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D018698:Glutamic Acid; D004533:Egtazic Acid; D002118:Calcium