Reduced ethanol inhibition of N-methyl-D-aspartate receptors by deletion of the NR1 C0 domain or overexpression of alpha-actinin-2 proteins

The depressant actions of ethanol on central nervous system activity appear to be mediated by its actions on a number of important membrane associated ion channels including the N-methyl-D-aspartate (MMDA) subtype of ionotrop ic glutamate receptor. Although no specific site of action for ethanol on t he NMDA receptor has been found, previous studies suggest that the ethanol sensitivity of the receptor may be affected by intracellular C-terminal dom ains of the receptor that regulate the calcium-dependent inactivation of th e receptor. In the present study, co-expression of the NR2A subunit and an NR1 subunit that lacks the alternatively spliced intracellular C1 cassette did not reduce the effects of ethanol on channel function as measured by pa tch-clamp electrophysiology, Full inhibition was also observed in cells exp ressing an NR1 subunit truncated at the end of the CO domain (NR1(863stop)) . However, the inhibitory effects of ethanol were reduced by expression of an NR1 CO domain deletion mutant (NR1 Delta(839-863)), truncation mutant (N R1(858stop)), or a triple-point mutant (Arg to Ala, Lys to Ala, and Asn to Ala at 859-861) previously shown to significantly reduce calcium-dependent inactivation. A similar reduction in the effects of ethanol on wild-type NR 1/2A but not NR1/2B or NR1/2C receptors was observed after co-expression of full-length or truncated human skeletal muscle alpha-actinin-2 proteins th at produce a functional knockout of the C0 domain. The effects of ethanol o n hippocampal and cortical NMDA-induced currents were similarly attenuated in low calcium recording conditions, suggesting that a C0domain-dependent p rocess may confer additional ethanol sensitivity to NMDA receptors.