The 71 kDa glutamate-binding protein is increased in cerebellar granule cells after chronic ethanol treatment

Besides the N-methyl-D-aspartate (NMDA) receptor proteins NR1 and NR2, another complex of proteins which has been shown to contain ligand-binding sites characteristic of NMDA receptors is expressed in cerebellar granule cells. One of the proteins in the latter complex is the 71 kDa glutamate-binding protein (GBP). To determine the role of the GBP in the response to NMDA, primary cultures of cerebellar granule cells were treated with an antisense oligonucleotide complementary to mRNA for this protein. This treatment substantially reduced both mRNA and protein levels of the GBP, as well as the response of the cells to NMDA, measured as an increase in intracellular Ca2+ with fura-2 fluorescence. The antisense oligonucleotide treatment did not alter the Ca2+ responses to KC1 or kainate. Chronic ethanol exposure has previously been shown to increase NMDA receptor function and the density of binding sites for the NMDA receptor channel blocker, dizocilpine, in cerebellar granule cells. Chronic exposure of the cells to 100mM ethanol is now shown to result in significant increases in mRNA and protein levels for the GBP (45% and 100%, respectively). Ethanol treatment did not affect mRNA levels for NR1 or NR2A, caused only a small increase (20%) in protein levels for NR1, and resulted in a decrease (30%) in NR2A protein. Although a role of the NMDA receptor NR1/NR2 subunits cannot be ruled out, these results are compatible with the hypothesis of involvement of the GBP in the chronic ethanol-induced increase in NMDA receptor function in cerebellar granule cells.