Effects of anti-glutamate-binding protein antibodies on synaptic membrane ion flux, glutamate transport and release, and L-glutamate binding activities.
Antibodies (Abs) raised against the L-glutamate-binding protein (GBP) purified from bovine brain were used to define the possible physiologic activity of GBP in synaptic membranes. Three processes were examined for their sensitivity to the Abs: the excitatory amino acid stimulation of thiocyanate (SCN-) flux, the transport of L-glutamic acid across the synaptic membrane, and the depolarization-induced release of L-glutamate. Only the amino acid-induced changes in ion flux were inhibited by the anti-GBP Abs. The change in membrane potential produced by exposure of synaptic membranes to excitatory amino acids was measured as the increase in the uptake of the lipophilic anion SCN-. The L-glutamate-induced SCN- influx was 40 times more sensitive to inhibition by the anti-GBP Abs than the stimulation of ion flux by kainate, and 60 times more sensitive than that produced by quisqualate. The anti-GBP Abs did not inhibit the activation of ion flux produced by N-methyl-D-aspartate. The inhibition of glutamate-stimulated ion fluxes by the Abs was complete, whereas the inhibition of L-glutamate binding to either the rat or bovine brain GBP was not. The results obtained indicated that although the majority of the anti-GBP Abs were not directed against the glutamate recognition site of the GBP and of presumed synaptic membrane receptors, they were effective in blocking the activation of receptor-associated ion channels. Thus, the GBP may be considered a component of some excitatory amino acid receptor complexes.
Roy
S
S
Galton
N
N
Michaelis
E
E
D000818:Animals; D000906:Antibodies / Q000276:immunology*; D001224:Aspartic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D001692:Biological Transport; D002417:Cattle; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D066298:In Vitro Techniques; D008564:Membrane Potentials; D016202:N-Methylaspartate; D051381:Rats; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000276:immunology* / Q000378:metabolism; D012964:Sodium / Q000494:pharmacology; D013570:Synaptic Membranes / Q000378:metabolism*; D013861:Thiocyanates / Q000378:metabolism*
D000906:Antibodies; D005971:Glutamates; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D013861:Thiocyanates; D001224:Aspartic Acid; D018698:Glutamic Acid; D016202:N-Methylaspartate; D012964:Sodium; C031760:thiocyanate