Excitatory Amino Acids Stimulate Inositol Phospholipid Hydrolysis and Reduce Proliferation in Cultured Astrocytes

Excitatory amino acids stimulated inositol phospholipid hydrolysis in primary cultures of astrocytes, as reflected by an increased formation of 3H]inositol monophosphate ( 3H]InsP) in the presence of 10 mM Li+. Quisqualate was the most potent activator of inositol phospholipid hydrolysis, followed by glutamate and ibotenate. Kainate exhibited low activity, whereas N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methylisoxazolepropionate (AMPA) were inactive. The increase in 3H]InsP formation induced by glutamate was potentiated after 12-h exposure to the proliferative agent epidermal growth factor (EGF), suggesting that activation of the mitotic cycle leads to an enhanced coupling of glutamate recognition sites with phospholipase C. To study how glutamate receptors are involved in regulating cell proliferation, we have measured methyl-3H]thymidine incorporation in cultured astrocytes. Excitatory amino acids reduced thymidine incorporation with a pharmacological profile similar to that observed for the stimulation of inositol phospholipid hydrolysis. Quisqualate acted as a potent antiproliferative agent, both under basal conditions and in cells stimulated to proliferate by addition of EGF or phorbol 12-tetradecanoate 13-acetate. Glutamate and ibotenate reduced methyl-3H]thymidine incorporation at high concentrations, whereas kainate, AMPA, and NMDA were virtually inactive. The action of quisqualate on both inositol phospholipid hydrolysis and thymidine incorporation was attenuated by 2-amino-4-phosphonobutyrate, which acted as a weak agonist/competitive antagonist. Other excitatory amino acid receptor antagonists were not effective.(ABSTRACT TRUNCATED AT 250 WORDS)