Tarantula toxin and pain

The bad guys are sometimes the good guys when nature makes them so. There had to be some reason for those hairy little creatures, the tarantulas, to be on Earth. Even the TRPV-1 receptor has been rehabilitated slightly by the discovery that it plays a vital role in preventing sepsis when humans are exposed to endotoxins (see Clark in current edition of FASEB).

French scientists, Mazzuca et al, are reporting in this months Nat Neurosci (2007) that a tarantula peptide from the South American spider Tarantula Psalmopoeus cambridgei is a POTENT inhibitor of thermal, mechanical, chemical, inflammatory and neuropathic pain.

This could be really big news, along the lines perhaps of ziconotide.

This toxin bears the unlikely name of psalmotoxin 1, and we never expected a biblical name to be associated with a toxin against pain. Yea, though I walk through the valley of the shadow of central pain, I will fear no tarantula. Tbis doesn’t really work, unless perhaps it does.

Psalmotoxin stops pain by “blocking acid-sensing ion channel 1a, and this blockade results in an activation of the endogenous enkephalin pathway ” You have already read here about how important it is to block acids in preventing pain. The ASIC 1a channel is one big reason. It is one of the ion channels in the cell membrane of the pain neuron.

Mazzuca and colleagues have determined that “the analgesic properties of the peptide are suppressed by antagonists of the mu and delta-opioid receptors”. This would indicate that blocking opiate receptors suppresses psalmotoxin, so don’t go out hunting tarantulas if you are taking opiates. We always knew you couldn’t depend on exogenous opioids for central pain. Besides, some of the other venoms in this little beastie may be very unpleasant.