Maitotoxin-evoked gamma-aminobutyric acid release is due not only to the opening of calcium channels.
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.
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
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