Complete and reversible block by ω-grammotoxin SIA of glutamatergic synaptic transmission between cultured rat hippocampal neurons

ω-Grammotoxin SIA (ω-GsTx SIA), a peptide isolated from tarantula venom, inhibits synaptosomal Ca²⁺ influx and neurotransmitter release, and blocks N-, P-, and Q-type voltage-gated Ca²⁺ channels. The whole-cell patch-clamp was used to record glutamatergic excitatory post-synaptic currents (EPSCs) evoked by extracellular stimulation of presynaptic neurons in primary rat hippocampal cultures. EPSCs displayed rapid kinetics and were blocked by CNQX. ω-Conotoxin (1 μM) GVIA inhibited EPSCs by 46%, while 30 nM and 1 μM ω-agatoxin IVA produced 12% and 69% inhibition, respectively, consistent with coupling of N-, P- and Q-type Ca²⁺ channels to glutamatergic synaptic transmission. ω-GsTx SIA (1 μM) rapidly, completely, and reversibly blocked glutamatergic EPSCs, but did not affect currents evoked by bath application of kainate. Thus, ω-GsTx SIA blocks glutamatergic synaptic transmission by blocking presynaptic voltage-gated Ca²⁺ channels. ω-GsTx SIA is the only agent that blocks selectively and reversibly the Ca²⁺ channels coupled to glutamate release. ω-GsTx SIA provides a unique and powerful tool for experiments requiring recovery of function following presynaptic block of synaptic transmission.