This fortnight’s post has been a bit late in coming since I’ve been caught up in some academic work, nonetheless, here is a selection that will fuel the fears of arachnophobes. Phoneutria nigriventer is a species of Brazilian wandering spider, and while it is not as venomous as another species in the same genus, P.fera, I’ve chosen it for examination because it is well documented.
As with the other candidates I’ve posted about in this series, it is venom that makes it deadly.
The venom’s main component is a peptide called PhTx3 , which is capable of blocking calcium channels that maintain the ion gradients needed by muscles to be able to contract properly following neural activity by motor neurons at the neuromuscular junction. This means that it can inhibit acetylcholine signalling and therefore trigger paralysis. If you wish to delve into the literature here, please see
this paper which details the evidence for the venom being a calcium channel blocker.
There is also a rather unsavoury aspect to P.nigriventer envenomation; it can induce priapism in humans, which is a condition where an erect reproductive appendage doesn’t return to a flaccid state for an abnormally long time; in this case, symptoms can apparently last for hours and may lead to impotence as an aftereffect.
This however also makes it a suitable research candidate for treatments of erectile dysfunction, go figure.
If you need help with that, here is the research paper that describes the confirmation of the activity of one of the components as a potentiator of erectile function in mice http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3019117/?tool=pmcentrez
If you’re interested in going through the amino acid sequences of the proteins in the venom, you may find the following database retrieval results sheet useful http://www.ncbi.nlm.nih.gov/protein?term=Phoneutria%20nigriventer
So guess that is it for this fortnight’s deadly organism of the week.