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Allosteric Regulation of the N ‐Methyl‐ d ‐Aspartate Receptor‐Linked Ion Channel Complex and Effects of Ethanol in Ethanol‐Withdrawal Seizure‐Prone and ‐Resistant Mice
Author(s) -
Carter Leslie A.,
Belknap John K.,
Crabbe John C.,
Janowsky Aaron
Publication year - 1995
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1995.64010213.x
Subject(s) - allosteric regulation , ethanol , chemistry , ion channel , receptor , neuroscience , microbiology and biotechnology , biochemistry , pharmacology , biophysics , biology
The effects of ethanol, glycine, and spermidine on the specific binding of [ 3 H]MK‐801 were characterized in Triton‐treated membranes prepared from the hippocampus and cortex of ethanol‐withdrawal seizure‐prone (WSP) and ‐resistant (WSR) mice. Glycine, an allosteric agonist at the NMDA receptor‐linked ion channel complex, caused an increase in specific [ 3 H]MK‐801 binding to hippocampal membrane preparations. There were no significant differences in EC 50 values between the selected lines for the effect of glycine (WSP, 391.7 ± 48.4 n M ; WSR, 313.4 ± 77 n M ) in the presence of 10 µ M NMDA or in the maximal response to the agonist (WSP, 1.75 ± 0.26 pmol/mg of protein; WSR, 1.67 ± 0.22 pmol/mg of protein). The EC 50 values for the spermidine‐induced increase in [ 3 H]MK‐801 binding in membranes from hippocampus in the absence (WSP, 11.7 ± 0.83 µ M ; WSR, 9.98 ± 1.29 µ M ) or in the presence of 10 µ M glycine and 10 µ M NMDA (WSP, 2.1 ± 0.35 µ M ; WSR, 2.37 ± 0.42 µ M ) also did not differ. Similar results were obtained in cortical membranes. Saturation isotherms indicated that there was no difference in the density of [ 3 H]MK‐801 binding sites, or in their affinity for the radioligand, between the mouse lines. In addition, administration of ethanol by inhalation (24 h) to WSP and WSR mice did not cause an increase in the density of [ 3 H]MK‐801 binding sites, and there was no difference in the density or affinity of binding sites between the mouse lines. Withdrawal from ethanol (6 h), which causes an increase in the severity of handling‐induced convulsions in WSP mice, also did not alter the binding site density or affinity for radioligand. The results suggest that the characteristics of the NMDA receptor‐linked ion channel complex in the tissue preparations described here do not differ in WSP and WSR mice. Thus, genetic differences in seizure susceptibility during ethanol withdrawal can be dissociated from the total density of hippocampal or cortex NMDA receptors under activating conditions.