title: Characterization of the exocytotic release of glutamate from guinea-pig cerebral cortical synaptosomes.
abstract: A continuous enzyme-linked fluorometric assay was used for determining the characteristics for glutamate exocytosis from guinea-pig cerebrocortical synaptosomes. Ca2+-dependent release can be induced not only by K+, but also by the Na+ channel activator veratridine and the Ca2+ ionophore ionomycin. K+-induced release can be inhibited by the Ca2+ channel inhibitor verapamil. Sr2+ and Ba2+ substitute for Ca2+ in promoting K+-induced release. Agents that would be predicted to transform the transvesicular pH gradient into a membrane potential are without effect on glutamate release. However, the protonophore carbonylcyanide p-trifluoromethoxyphenylhydrazone causes a time-dependent loss of exocytosis that is oligomycin insensitive and may be due to depletion of vesicular glutamate. The Ca2+-independent release of glutamate from the cytosol on depolarization is unchanged or promoted by metabolic inhibitors that lower the ATP/ADP ratio. In contrast. Ca2+-dependent release is ATP dependent and is blocked by the combined inhibition of oxidative phosphorylation and glycolysis.
mesh_terms: D000255:Adenosine Triphosphate / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000502:physiology; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone / Q000494:pharmacology; D002540:Cerebral Cortex / Q000378:metabolism*; D004734:Energy Metabolism; D004987:Ethers / Q000494:pharmacology; D005089:Exocytosis; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D006168:Guinea Pigs; D006863:Hydrogen-Ion Concentration; D015759:Ionomycin; D010042:Ouabain / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology; D014701:Veratridine / Q000494:pharmacology
chemical_list: D004987:Ethers; D005971:Glutamates; D002259:Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; D018698:Glutamic Acid; D015759:Ionomycin; D010042:Ouabain; D014701:Veratridine; D000255:Adenosine Triphosphate; D014700:Verapamil; D002118:Calcium