Destabilisation of the SNARE complex by the binding of calcium channel blocking toxin from Phoneutria nigriventer spider venom

Abstract

Aims: This study describes the alterations induced in the neurolransmitter release machinery function by the interaction of a peptide toxin PF3 which strongly interacts with calcium channels associated to neurotransmitter release. Methods and Results: Neurotransmilter release funclion was evaluated by the release of labelled acetylcholine previously incorporated to the functional pool of neurotransmitter in rat striatal chopped tissue in the presence and absence of Ca"' using a superfusion apparatus. Results show that in the presence of Ca'', PF3 decreased *HAcetylcholine release while in the absence of Ca" PF3 increased *H-Acetylcoline release. Previous results have demonstrated that PF3 interacts reversibly with calcium channels in the presence of Ca"' and irreversibly in the absence of this ion. The strong and irreversible binding of PF3 to the P/Q and N type calcium channel in calcium-free conditions could destabilise the proteic machinery involved in neurotransmitter release and induce the observed increase in 3H-acetylcholine release. Alternatively, the lack of Ca** may impair membrane recycling after exocytosis and consequently, revert the vesicular choline transporter leading to an extrusion of *H-choline producing an apparent increase in release. These hypotheses will be challenged in future experiments. Conclusions: These results represent an unexpected effect of the calcium channel blocker PF3, and may represent a direct proof of the proposed association of calcium channels with the SNARE complex.