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 [3H]inositol phosphates in the presence of lithium in cells prelabelled with [3H]inositol. Acute exposure to 200 mM ethanol had no significant effect on either basal or L-glutamate stimulated [3H]inositol phosphate formation. In cells chronically exposed to ethanol for 4 days, the [3H]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 [3H]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.
Smith
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Department of Veterans Affairs Medical Center, Research Service (151), Tucson, Arizona 85723.
D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000201:enzymology*; D002478:Cells, Cultured; D002540:Cerebral Cortex / Q000166:cytology; D003515:Cycloleucine / Q000031:analogs & derivatives / Q000494:pharmacology; D016232:Endothelins / Q000494:pharmacology; D000431:Ethanol / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D018698:Glutamic Acid / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D007295:Inositol Phosphates / Q000378:metabolism; D008094:Lithium / Q000494:pharmacology; D011247:Pregnancy; D016318:Quisqualic Acid / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D014316:Tritium; D010738:Type C Phospholipases / Q000378:metabolism*
D016232:Endothelins; D007295:Inositol Phosphates; D018094:Receptors, Metabotropic Glutamate; D003515:Cycloleucine; D014316:Tritium; C036361:1-amino-1,3-dicarboxycyclopentane; D000431:Ethanol; D018698:Glutamic Acid; D006160:Guanosine Triphosphate; D016318:Quisqualic Acid; D008094:Lithium; D010738:Type C Phospholipases