Inhibition of neuronal tetrodotoxin-sensitive Na+ channels by two spider toxins: hainantoxin-III and hainantoxin-IV.
Hainantoxin-III and hainantoxin-IV, isolated from the venom of the Chinese bird spider Seleconosmia hainana, are neurotoxic peptides composed of 33-35 residues with three disulfide bonds. Using whole-cell patch-clamp technique, we investigated their action on ionic channels of adult rat dorsal root ganglion neurons. It was found that the two toxins did not affect Ca2+ channels (both high voltage activated and low voltage activated types) nor tetrodotoxin-resistant voltage-gated Na+ channels (VGSCs). However, hainantoxin-III and hainantoxin-IV strongly depressed the amplitude of tetrodotoxin-sensitive Na+ currents with IC50 values of 1.1 and 44.6 nM, respectively. Both hainantoxin-III (1 nM) and hainantoxin-IV (50 nM) caused a hyperpolarizing shift of about 10 mV in the voltage midpoint of steady-state Na+ channel inactivation, but they showed difference in the reprime kinetics of VGSCs: hainantoxin-III significantly decreased the recovery rate from inactivation at a prepulse potential of -80 mV while hainantoxin-IV did not do. It is interesting to note that similar to huwentoxin-IV, the two hainantoxins did not affect the activation and inactivation kinetics of Na+ currents and at a concentration of 1 microM they completely inhibited the slowing inactivation currents induced by BMK-I (toxin I from the scorpion Buthus martensi Karsch), a scorpion alpha-like toxin. The results indicate that hainantoxin-III and hainantoxin-IV are novel spider toxins and affect the mammal neural Na+ channels through a mechanism quite different from other spider toxins targeting the neural receptor site 3, such as delta-aractoxins and mu-agatoxins.
D000595:Amino Acid Sequence; D000818:Animals; D005260:Female; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D008297:Male; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D051381:Rats; D017207:Rats, Sprague-Dawley; D026941:Sodium Channel Blockers / Q000494:pharmacology*; D015222:Sodium Channels / Q000187:drug effects* / Q000502:physiology; D013111:Spider Venoms / Q000494:pharmacology*; D013779:Tetrodotoxin / Q000494:pharmacology*; D013997:Time Factors
D026941:Sodium Channel Blockers; D015222:Sodium Channels; D013111:Spider Venoms; C488683:hainantoxin III, Seleconosmia hainana; C474037:hainantoxin-IV, Seleconosmia hainana; D013779:Tetrodotoxin