The peptide toxin δ-hexatoxin-MrIX inhibits fast inactivation of NaVs in mouse cerebellar granule cells

Abstract

Spider venom is rich in peptide toxins that could be used to explore the structure and function of voltage-gated sodium channels (Na_Vs). This study has characterized a 44-amino acid peptide toxin, δ-hexatoxin-MrIX (δ-HXTX-MrIX), from the venom of the spider Macrothele raveni. δ-hexatoxin-MrIX potently inhibited the fast inactivation of Na_Vs in mouse cerebellar granule cells (CGCs) with an EC₅₀ of 35.3 ± 5.9 nM. The toxin shifted both the steady-state activation and the steady-state inactivation curves of CGC Na_Vs to the hyperpolarized direction. δ-hexatoxin-MrIX also acted on Na_V1.3 and Na_V1.4 channels heterologously expressed in HEK293T cells, as well as on Na_Vs in acutely isolated cockroach DUM neurons. However, the Na_V1.5, Na_V1.7 and Na_V1.8 channels were resistant to δ-hexatoxin-MrIX. The toxin inhibited the fast inactivation of Na_V1.3 and Na_V1.4 with high affinity (EC₅₀ values of 82.0 ± 3.0 nM and 24.0 ± 4.7 nM, respectively), but the saturating dose of toxin showed distinct efficacy on these two types of channels. δ-hexatoxin-MrIX is a peptide toxin acting on CGC Na_Vs and could be used as a pharmacological tool to explore the role of Na_Vs in granule cell maturation during cerebellum development.

Keywords: Cerebellar granule cell; Voltage-gated sodium channel; δ-hexatoxin-MrIX.