Lack of involvement of [Ca2+]i in the external Ca(2+)-independent release of acetylcholine evoked by veratridine, ouabain and alpha-latrotoxin: possible role of [Na+]i.
Synaptosomes were challenged by veratridine, ouabain and alpha-latrotoxin, and the release of 14C-acetylcholine (ACh) was measured in the absence of external Ca2+. We wished to test whether Ca2+ mobilized from internal stores triggered the ACh release that was independent of external Ca2+. We found that none of the agents altered the [Ca2+]i in a Ca(2+)-free medium. Buffering the intracellular Ca2+ concentration with BAPTA did not prevent the increase in release of 14C-ACh by veratridine or ouabain in the absence of Ca2+, however, it greatly reduced the release evoked in a Ca(2+)-containing medium. In parallel samples the release of ACh and the change in the internal Na+ concentration ([Na+]i) were measured. It was found that veratridine, ouabain and alpha-latrotoxin all enhanced [Na+]i in a concentration-dependent manner and a good quantitative relationship existed between the increase in [Na+]i and the release of ACh.
Adam-Vizi
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V
Department of Biochemistry II, Semmelweis University of Medicine, Budapest, Hungary.
Deri
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Z
Bors
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Tretter
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L
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006168:Guinea Pigs; D007425:Intracellular Membranes / Q000378:metabolism*; D009994:Osmolar Concentration; D010042:Ouabain / Q000494:pharmacology*; D012964:Sodium / Q000378:metabolism / Q000502:physiology; D013111:Spider Venoms / Q000494:pharmacology*; D013574:Synaptosomes / Q000378:metabolism; D014701:Veratridine / Q000494:pharmacology*
D013111:Spider Venoms; D004533:Egtazic Acid; D010042:Ouabain; C020763:alpha-latrotoxin; D014701:Veratridine; D012964:Sodium; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D000109:Acetylcholine; D002118:Calcium