| 11821145 |
Storchak LG, Linetska MV, Himmelreich NH: Does extracellular calcium determine what pool of GABA is the target for alpha-latrotoxin?. Neurochem Int. 2002 Apr;40(5):387-95.
Presynaptic neurotoxin alpha-latrotoxin, from the venom of Latrodectus mactans tredecimguttatus, causes massive [(3) H] GABA release from rat brain synaptosomes, irrespective of calcium presence in the extracellular medium. Whether the binding of alpha-latrotoxin to Ca (2+)-dependent (neurexin 1 alpha) or to Ca (2+)-independent (latrophilin) receptor triggers [(3) H] GABA release by the same mechanisms or different ones, inducing either exocytotic process or outflow by mobile membrane GABA transporter, is unknown. We examined alpha-latrotoxin-evoked [(3) H] GABA release from synaptosomes which cytosolic [(3) H] GABA pool was depleted either by applying competitive inhibitors of the GABA transporter, nipecotic acid and 2,4-diaminobutyric acid, or by permeation with digitonin. We also compared the effect of the GABA transporter inhibitors on depolarisation-evoked and alpha-latrotoxin-evoked [(3) H] GABA release using as depolarising agents 4-aminopyridine and high KCl in the Ca (2+)-containing and in Ca (2+)-free medium, respectively. Incubation of synaptosomes with nipecotic acid induced the essential acceleration of unstimulated [(3) H] GABA release and deep inhibition of high KCl-evoked Ca (2+)-independent [(3) H] GABA release. In contrast, at the similar conditions the effect of alpha-latrotoxin was greatly augmented with respect to the control response. Another way to assay what GABA pool was involved in alpha-latrotoxin-induced release lays in an analysis of the effects of depolarisation and alpha-latrotoxin in consecutive order. The preliminary 4-aminopyridine-stimulated [(3) H] GABA release attenuated the toxin effect. But when depolarisation occurred in Ca (2+)-free medium, no influence on alpha-latrotoxin effect was revealed. Employing digitonin-permeated synaptosomes, we have shown that alpha-latrotoxin could stimulate [3H] GABA release in the medium with 1mM EGTA, this effect of the toxin was blocked by concanavalin A and was ATP-dependent. The latter suggests that alpha-latrotoxin-released neurotransmitter has the vesicular nature. We assume that the type of the toxin membrane receptor does not determine the mechanisms of [(3) H] GABA release evoked by alpha-latrotoxin. |
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