title: Magnesium-dependent inhibition of agonist-stimulated phosphoinositide breakdown in rat cortical slices by excitatory amino acids.
abstract: The excitatory amino acid agonists kainate, N-methyl-D-aspartate (NMDA), and quisqualate inhibited ligand-stimulated phosphoinositide hydrolysis in rat cortical slices. The NMDA channel blocker MK-801 antagonized the inhibition by NMDA but had no effect on the inhibition due to kainate or quisqualate. The antagonist 6-cyano-7-nitroquinoxaline-2,3-dione blocked the effects of quisqualate and kainate but not the effect of NMDA. These data indicate that activation of the NMDA, alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid, and kainate types of ionotropic receptors has the same effect. In membranes prepared from cortical slices, there was no inhibition of carbachol-stimulated phosphoinositidase C activity by excitatory amino acids, suggesting that excitatory amino acids indirectly affect carbachol-stimulated phosphoinositide hydrolysis. The inhibition by excitatory amino acids of carbachol-stimulated phosphoinositide breakdown was dependent on extracellular Mg2+ and was abolished by procedures that increase intracellular Ca2+. Veratridine inhibition of carbachol-stimulated phosphoinositide hydrolysis was reversed by ouabain but not by other procedures that increase intracellular Ca2+. In contrast to excitatory amino acids, veratridine potentiated carbachol-stimulated phosphoinositide breakdown in the presence of 10 mM extracellular Mg2+. These data suggest that excitatory amino acids inhibit carbachol-stimulated phosphoinositide breakdown in rat cortex by lowering intracellular Ca2+ through a mechanism dependent on extracellular Mg2+.
authors.affiliation: Department of Biochemistry, University of Tennessee, Memphis 38163.
authors.forename: H M
authors.initials: HM
authors.lastname: Lee
authors.forename: J N
authors.initials: JN
authors.lastname: Fain
mesh_terms: D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002217:Carbachol / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D002540:Cerebral Cortex / Q000378:metabolism*; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology*; D008297:Male; D016202:N-Methylaspartate / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000596:Amino Acids; D002121:Calcium Channel Blockers; D010716:Phosphatidylinositols; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D016202:N-Methylaspartate; D015544:Inositol 1,4,5-Trisphosphate; D002217:Carbachol; D008274:Magnesium; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium