This toxin is a potent and practically irreversible antagonist of both Cav2.1/CACNA1A and Cav2.2/CACNA1B calcium channels, while it displays a partial and rapidly reversible block of Cav2.3/CACNA1E calcium channels and no effect on Cav3/CACNA1 calcium channels. Inhibits glutamate uptake from rat brain synaptosomes by an interaction between cysteines from both glutamate transporter and toxin. Blocks potassium-induced exocytosis of synaptic vesicles in brain cortical synaptosomes with an IC(50) of 1.1 nM. In mice, induces rapid general flaccid paralysis followed by death in 10-30 minutes at dose levels of 5 ug per mouse. In rat brain, inhibits glutamate release, neuronal death and loss of neurotransmission in the hippocampus resulting from ischemia. Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Could be used as a diagnostic tool for the autoimmune disease Lambert-Eaton myasthenic syndrome. Belongs to the neurotoxin 04 (omega-agtx) family. 03 (type II/III omega-agtx) subfamily.