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Effects of ethanol on GluN1/GluN2A and GluN1/GluN2B NMDA receptor-ion channel gating kinetics.

R. Peoples,H. Ren

Published 2022 in Alcoholism: Clinical and Experimental Research

ABSTRACT

BACKGROUND The N-methyl-D-aspartate receptor (NMDAR) is a major molecular target of alcohol action in the central nervous system, yet many aspects of the manner in which alcohol modulates the activity of this ion channel remain unclear. We and others have shown that ethanol inhibition of NMDAR involves alterations in gating, especially reduction of mean open time. A full description of ethanol's effects on NMDAR kinetics, however, including fitting to a kinetic model, has not been reported. METHODS To determine ethanol's effects on NMDAR kinetics, we used steady-state single-channel recording in outside-out patches from HEK-293 cells transfected with recombinant GluN1/GluN2A or GluN1/GluN2B NMDAR subunits. Very low glutamate concentrations were used in order to isolate individual activations of the receptor. RESULTS In both subunit types, ethanol, at approximate whole-cell IC50 values (156 mM, GluN2A; 150 mM, GluN2B), reduced open probability (Po ) by approximately 50%, and decreased mean open time without changing frequency of opening. Open and shut time distributions exhibited two and five components, respectively; ethanol selectively decreased the time constant and relative proportion of the longer open time component. In the GluN2A subunit, ethanol increased the time constants of all but the longest shut time components, whereas in the GluN2B subunit, shut times were unchanged by ethanol. Fitting of bursts of openings (representing individual activations of the receptor) to the gating portion of a kinetic model revealed that ethanol altered two rates: the rate associated with activation of the GluN2A or GluN2B subunit, and the rate associated with closing of the longer of the two open states. CONCLUSIONS These results demonstrate that ethanol selectively alters individual kinetic rates, and thus appears to selectively affect distinct conformational transitions involved in NMDAR gating.

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