title: Modulation of carbachol-stimulated inositol phospholipid breakdown in rat cerebral cortical miniprisms by excitatory amino acids and by BAY K-8644 is dependent upon the assay calcium and potassium concentrations used.
abstract: The calcium and potassium ion dependency of the inositol phospholipid breakdown response to stimulatory agents has been investigated in rat cerebral cortical miniprisms. The calcium channel agonist BAY K-8644 (10 microM) potentiated the response to carbachol at 6 mM K+ when Ca2(+)-free, but not when 2.52 mM Ca2+ assay buffer was used. In Ca2(+)-free buffer, verapamil (10 microM) inhibited the response to carbachol at both 6 and 18 mM K+ but higher concentrations (30-300 microM) were needed when 2.52 mM Ca2+ was used. At these higher concentrations, however, verapamil inhibited the binding of 2 nM [3H]pirenzepine to muscarinic recognition sites. N-Methyl-D-Aspartate (NMDA, 100 microM) significantly reduced the basal phosphoinositide breakdown rate at 18 mM K+ at 1.3 mM Ca2+, but was without effect on the basal rate at other K+ and Ca2+ concentrations. In the presence of NMDA (100 microM) or quisqualate (100 microM), the responses to carbachol were reduced, the degree of reduction showing a complex dependency upon the assay K+ and Ca2+ concentrations used. These results indicate that the inositol phospholipid breakdown response to carbachol in cerebral cortical miniprisms can be modulated in a manner dependent upon the extracellular calcium and potassium concentrations used.
authors.affiliation: Department of Pharmacology, University of Umeå, Sweden.
authors.forename: G
authors.initials: G
authors.lastname: Tiger
authors.forename: C J
authors.initials: CJ
authors.lastname: Fowler
mesh_terms: D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000596:Amino Acids / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D002217:Carbachol / Q000494:pharmacology*; D002540:Cerebral Cortex / Q000033:anatomy & histology / Q000187:drug effects / Q000378:metabolism*; D007295:Inositol Phosphates / Q000378:metabolism*; D007700:Kinetics; D016202:N-Methylaspartate / Q000494:pharmacology; D009994:Osmolar Concentration; D010743:Phospholipids / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology*; D016318:Quisqualic Acid / Q000494:pharmacology; D051381:Rats
chemical_list: D000596:Amino Acids; D007295:Inositol Phosphates; D010743:Phospholipids; D016202:N-Methylaspartate; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D016318:Quisqualic Acid; D002217:Carbachol; D011188:Potassium; D002118:Calcium