Hainantoxin-III is a 33 amino acid peptidyl toxin isolated from the Haplopelma hainanum (Selenocosmia hainana, Chinese bird) tarantula spider.
Hainantoxin-III strongly depresses the amplitude of TTX-sensitive Na+ currents with IC50 value of 1.1 nM. It causes a hyperpolarizing shift of about 10 mV in the voltage midpoint of steady-state Na+ channel inactivation and significantly decreases the recovery rate from inactivation.
The Haplopelma hainanum tarantula spider venom was recently found to be a source of various toxic components with different pharmacological properties. 192 mature toxin sequences were identified by DNA sequencing technique. Hainantoxin-III was one of the toxins identified.