title: Maitotoxin-evoked gamma-aminobutyric acid release is due not only to the opening of calcium channels.
abstract: The effects of maitotoxin (MTX) on endogenous amino acid release were tested on highly purified striatal neurons differentiated in primary culture. MTX induced a large and concentration-dependent release of gamma-aminobutyric acid (GABA). This effect was abolished when experiments were performed in the absence of external Ca2+, and restored when Ca2+ ions were added after removing the MTX-containing Ca2+-free solution. MTX-induced amino acid release was not affected by 1 microM nifedipine and only slightly inhibited by 1 mM Co2+. MTX also induced a massive accumulation of 45Ca2+ in the neurons which, in contrast to the MTX-evoked GABA release, was totally blocked in the presence of 1 mM Co2+. Whereas 500 nM tetrodotoxin was without significant effect, MTX-evoked GABA release was dependent on the presence of external Na+ and sensitive to nipecotic acid, a GABA uptake inhibitor. It is concluded that, on striatal neurons, MTX induced Na+ influx only in the presence of external Ca2+. The increase in cytoplasmic Na+ ions then triggers the release of GABA.
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D003035:Cobalt / Q000494:pharmacology; D003342:Corpus Striatum / Q000166:cytology*; D004622:Embryo, Mammalian; D007473:Ion Channels / Q000187:drug effects / Q000378:metabolism*; D008387:Marine Toxins / Q000494:pharmacology*; D051379:Mice; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D009557:Nipecotic Acids / Q000494:pharmacology; D035964:Oxocins; D011392:Proline / Q000031:analogs & derivatives*; D012964:Sodium / Q000494:pharmacology; D013779:Tetrodotoxin / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*; D000095702:Polyether Toxins
chemical_list: D000596:Amino Acids; D002118:Calcium; D003035:Cobalt; D007473:Ion Channels; D008387:Marine Toxins; D009543:Nifedipine; D009557:Nipecotic Acids; D035964:Oxocins; D011392:Proline; D012964:Sodium; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; C030278:nipecotic acid; C020394:maitotoxin; D000095702:Polyether Toxins; C010983:homoproline