Inhibitory actions of synthesised polyamine spider toxins and their analogues on Ca 2+-activated Cl − currents recorded from cultured DRG neurones from neonatal rats

Abstract

The whole cell variant of the patch clamp technique was used to investigate the actions of polyamine spider toxins and their analogues on high voltage-activated Ca 2+ currents and Ca 2+-activated Cl − currents ( I Cl(Ca)). The actions of synthesised FTX (putative natural toxin from the American funnel web spider), sFTX-3.3, Orn-FTX-3.3, Lys-FTX-3.3, and argiotoxin-636 on cultured dorsal root ganglion neurones from neonatal rats were investigated. Synthesised FTX (1 μM) inhibited I Cl(Ca) but did not inhibit high voltage-activated Ca 2+ currents. In contrast, sFTX-3.3 (10 μM) inhibited both high voltage-activated Ca 2+ currents and the associated I Cl(Ca) in near equal proportions. Argiotoxin-636 (1–10 μM) inhibited I Cl(Ca) evoked by Ca 2+ entry through voltage-activated channels and by intracellular photorelease of Ca 2+ from a caged precursor DM-nitrophen. This data indicates that synthesised FTX and argiotoxin-636 directly inhibit Ca 2+-activated Cl − channels. In conclusion, the potency of polyamines as non-selective inhibitors of Ca 2+ channels and Ca 2+-activated Cl − channels is in part determined by the presence of a terminal arginine and this may involve an interaction between terminal guanidino groups and Ca 2+ binding sites.