title: Kainic acid inhibits the synaptosomal plasma membrane glutamate carrier and allows glutamate leakage from the cytoplasm but does not affect glutamate exocytosis.
abstract: Kainate inhibits the exchange of D-aspartate into guinea-pig cerebrocortical synaptosomes. Kainate inhibits the Ca2+-independent efflux of endogenous glutamate in the presence of a trapping system for the released amino acid but potentiates a Ca2+-independent net efflux of endogenous and labelled glutamate and aspartate in the absence of the trap. Dihydrokainate has a similar effect. No discrepancy is seen between the release of endogenous and exogenously accumulated amino acid. These results are consistent with the presence of a slow leak of glutamate or aspartate from the cytoplasm independent of the kainate-sensitive Na+-cotransport pathway. In the presence of the trap, glutamate effluxes by both pathways, whereas in the absence of the trap, the Na+-cotransport pathway opposes the leak. Neither in the presence or absence of the glutamate trap does kainate induce, inhibit, or otherwise affect the Ca2+-dependent release of endogenous glutamate. The results enable many of the apparent complexities in the presynaptic actions of kainate to be resolved.
mesh_terms: D027322:Amino Acid Transport System X-AG; D000818:Animals; D001224:Aspartic Acid / Q000378:metabolism; D002118:Calcium / Q000494:pharmacology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors*; D002462:Cell Membrane / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D005089:Exocytosis / Q000187:drug effects*; D005260:Female; D005969:Glutamate Dehydrogenase; D050491:Glutamate Plasma Membrane Transport Proteins; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D006168:Guinea Pigs; D007608:Kainic Acid / Q000494:pharmacology*; D008297:Male; D010539:Permeability; D027981:Symporters; D013574:Synaptosomes / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D027322:Amino Acid Transport System X-AG; D002352:Carrier Proteins; D050491:Glutamate Plasma Membrane Transport Proteins; D005971:Glutamates; D027981:Symporters; D001224:Aspartic Acid; D018698:Glutamic Acid; D005969:Glutamate Dehydrogenase; D007608:Kainic Acid; D002118:Calcium