title: Zinc deficiency decreases the concentration of N-methyl-D-aspartate receptors in guinea pig cortical synaptic membranes.
abstract: Zinc deficiency in guinea pigs decreases glutamate-stimulated calcium uptake in cortical synaptosomes. Glutamate not only stimulates calcium uptake but also potentiates the binding of the drug dizocilpine (MK-801) to an internal site of the N-methyl-D-aspartate receptor/calcium channel, a subtype of the glutamate receptor. The purpose of this study was to determine whether the effect of zinc deficiency on calcium uptake by glutamate-stimulated synaptosomes is related to N-methyl-D-aspartate receptor number or function, as measured by MK-801 binding. Immature guinea pigs consumed a low zinc (< 1 mg/kg) diet ad libitum or an adequate zinc (100 mg/kg) diet, either ad libitum or restricted to maintain weight similar to that of the low zinc animals. Binding of MK-801 to cortical membranes was measured first in the presence of saturating concentrations of glutamate or N-methyl-D-aspartate in combination with glycine. Zinc deficiency significantly reduced the concentration of MK-801 binding sites (20%) regardless of the potentiating agonist used, but had no effect on binding affinity. The binding of MK-801 in response to 1, 10 and 100 mumol/L glycine, in the presence of 100 nmol/L glutamate, was then measured and found to be significantly reduced (12%). The results suggest that zinc deficiency decreases the number of functional N-methyl-D-aspartate receptor/channels in cortical membranes, probably because of impaired channel opening.
authors.affiliation: Department of Biochemistry, University of Missouri, Columbia 65211, USA.
authors.forename: J D
authors.initials: JD
authors.lastname: Browning
authors.forename: B L
authors.initials: BL
authors.lastname: O'Dell
mesh_terms: D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D004032:Diet; D016291:Dizocilpine Maleate / Q000378:metabolism*; D005260:Female; D018698:Glutamic Acid / Q000494:pharmacology; D005998:Glycine / Q000494:pharmacology; D006168:Guinea Pigs; D008297:Male; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000378:metabolism*; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism; D014886:Weaning; D015032:Zinc / Q000097:blood / Q000172:deficiency*
chemical_list: D016194:Receptors, N-Methyl-D-Aspartate; D018698:Glutamic Acid; D016291:Dizocilpine Maleate; D015032:Zinc; D002118:Calcium; D005998:Glycine