Fyn kinase does not reduce ethanol inhibition of zinc-insensitive NR2A-containing N-methyl- d-aspartate receptors

Abstract

N-methyl- d-aspartate (NMDA) receptors are ion channels activated by the neurotransmitter glutamate and are important mediators of neuronal signal transduction. Ethanol inhibits ion flux through NMDA receptors at concentrations that are associated with behavioral signs of intoxication. The overall sensitivity of NMDA receptors to ethanol is influenced by factors, including subunit composition and interactions with cytoskeletal elements. Results of studies also support the suggestion that the ethanol inhibition on NR1/2A receptors is reduced by Fyn kinase–mediated tyrosine phosphorylation. However, tyrosine kinases also reduce the high-affinity zinc sensitivity of NR1/2A receptors, supporting the suggestion that kinase-dependent effects on ethanol inhibition may be secondary to relief of zinc inhibition. In the current study, the effect of Fyn kinase on the ethanol inhibition of NR1/2A receptors was determined under conditions in which zinc sensitivity is eliminated. Human embryonic kidney 293 (HEK 293) cells were transiently transfected with wild-type or mutant NMDA subunits, and glutamate-activated currents were measured by using patch-clamp electrophysiology. Inclusion of the tyrosine phosphatase inhibitor potassium bisperoxo(1,10-phenanthroline)oxovanadate (V) [bpV(phen)] in the recording pipette eliminated the potentiation of NR1/2A currents by heavy metal chelators. Under these conditions, Fyn kinase did not reduce ethanol inhibition of wild-type receptors. Fyn kinase also had no effect on the magnitude of ethanol inhibition of zinc-insensitive NR1/2A(H128S) receptors. Together, results of the current study indicate that Fyn kinase does not directly affect the ethanol sensitivity of NR1/2A receptors.