Transmitter release and presynaptic Ca2+ currents blocked by the spider toxin ω-Aga-IVA

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Mammalian neuromuscular transmission is resistant to L and N type calcium channel blockers but very sensitive to a low molecular weight funnel web spider venom toxin, FTX, which selectively blocks P type calcium channels. To further characterize the calcium channels involved in neuromuscular transmission we studied the effect of omega Agatoxin (ω-Aga-IVA) a polypeptide P type channel blocker from the same spider venom. We show that ω-Aga-IVA is a potent and irreversible inhibitor of the presynapitc Ca2+ currents and of acetylocholine release induced by electrical stimulation or by K+ depolarization. This provides further evidences that transmitter release at the mammalian neuromuscula junction is mediated by P type Ca2+ channels.

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