SELECTIVE EFFECTS OF ETHANOL EXPOSURE ON METABOTROPIC GLUTAMATE-RECEPTOR AND GUANINE-NUCLEOTIDE STIMULATED PHOSPHOLIPASE-C ACTIVITY IN PRIMARY CULTURES OF ASTROCYTES

The effects of acute and chronic ethanol exposures on the stimulation of inositol specific phospholipase C by metabotropic glutamate receptor activation were determined in primary cultures of rat cortical astrocytes. Phospholipase C activity was monitored by the formation of [H-3]inositol phosphates in the presence of lithium in cells prelabelled with [H-3]inositol. Acute exposure to 200 mM ethanol had no significant effect on either basal or L-glutamate stimulated [H-3]inositol phosphate formation. In cells chronically exposed to ethanol for 4 days, the [H-3]inositol phosphate responses to L-glutamate, quisqualate, and the selective metabotropic receptor agonist, 1S,3R-1-amino-cyclopentane-1,3 dicarboxylic acid (trans-ACPD), were significantly inhibited when compared to control (untreated) cells. In contrast, chronic ethanol exposure had no significant effect on the [H-3]inositol phosphate response to endothelin-1, a peptide structurally and functionally unrelated to L-glutamate. Similarly, the stimulation of [3H]inositol phosphate formation by the stable GTP analog, guanine 5' -(gamma-thiotrisphosphate), was also unaffected by chronic ethanol exposure. The results suggest that chronic ethanol exposure does not affect the coupling of GTP binding proteins to phospholipase C, but rather acts in a selective manner to either alter the metabotropic receptor number or to disrupt the normal coupling of this receptor to its GTP binding protein, which may in turn affect receptor affinity.