Low affinity binding to glutamate receptor sites correlates with depolarizing responses induced by glutamate and quisqualate in striatal synaptoneurosomes.
In the present study, binding affinity of glutamate and quisqualate to striatal synaptoneurosome membranes in the guinea-pig was compared with concentration-dependence of depolarizing responses induced by these agents. The displacement of radioactive glutamate from receptor binding site by unlabelled glutamate and quisqualate revealed a nonhomogeneous population of binding sites. A high affinity component of binding was observed with an inhibition constant of 0.04 microM for glutamate and 0.45 microM for quisqualate, as well as a low affinity component with an inhibition constant of 10 microM for glutamate and 87 microM for quisqualate. Changes of the membrane potential in striatal synaptoneurosomes induced by glutamate and quisqualate were detected by measuring the absorbance of a potential sensitive cyanine dye. Glutamate and quisqualate induced constantly a depolarization in synaptoneurosome particles. Concentration-response curves showed that half-maximal depolarization was obtained with 10 microM glutamate and 100 microM quisqualate. The comparison of the displacement data with the changes in the membrane potential in the present investigation indicate that in vitro glutamate and quisqualate depolarize striatal synaptoneurosome particles through low affinity binding to receptor site for glutamate.
Heinonen
E
E
Neurobiology Research Unit, University of Helsinki, Finland.
Leino
M
M
Akerman
K E
KE
D000818:Animals; D003342:Corpus Striatum / Q000187:drug effects*; D005260:Female; D005971:Glutamates / Q000494:pharmacology*; D018698:Glutamic Acid; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009467:Neuromuscular Depolarizing Agents / Q000494:pharmacology*; D016318:Quisqualic Acid / Q000494:pharmacology*; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter / Q000378:metabolism*; D013570:Synaptic Membranes / Q000187:drug effects / Q000378:metabolism; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*
D005971:Glutamates; D009467:Neuromuscular Depolarizing Agents; D017470:Receptors, Glutamate; D017981:Receptors, Neurotransmitter; D018698:Glutamic Acid; D016318:Quisqualic Acid