The effect of TTX on Garter Snakes?

I only know the bare bones about tetradotoxins, aswell as T. Granulosa. I just happened to see a documentary (no idea what it was called sorry, just happened to randomly find it on the TV) anyway it was on the Evolution of Toxic newts. Of course it focused on the rough-skinned newt and was talking about how the theory was that the newts toxcicity increased to higher levels because some species of garter snake was resistant to their toxins. Anyway I found it all very interesting but the one question they didn't is how the snake resists the toxin. I know it isn't a protein-based toxin so I suppose enzymes wouldn't do the job. This may be all completely wrong but I'd appreciate it if anyone could tell me a little bit more about how TTX works, and how the snake resists it.

Thanks,
Ian

Hi Ian,

I used to teach evolution for the professor who's done a lot of this work. I'll try to summarize what I know, and give you a link to a more in-depth description.

Basically, TTX works by blocking sodium channels in nerves. As you may or may not know, nerves use the propagation of action potentials - or waves of changing charge - along their lengths. The way this is done is by the movement of charged ions across the nerve cell's membrane. One of the most important ions in action potential propogation is sodium (Na+), which moves through a special sodium channel in the nerve.

The TTX toxin basically sits inside the sodium channel (which looks like a little pore), effectively blocking any sodium from entering or leaving. The nerve can't send impulses when this happens. And TTX is very potent, so a little will affect many nerves, basically stopping all movement, including breathing.

The resistant snakes have evolved a slightly differently shaped sodium channel, which isn't blocked as effectively by TTX. It's happened more than once, so different populations of snakes have differently modified channels.

Anyway, here's a more technical summary with pictures:

http://scienceblogs.com/pharyngula/2008/06/evolving_proteins_in_snakes.php

Hope that helps - there's actually a lot more interesting stuff about this system.

ETA: I actually have a pretty funny story about a visiting grad student who grabbed a Taricha out of a tank in this lab and licked it. And why he survived. I'll tell it if anyone's interested.

Thanks Erin, that's very intresting. And what's more it makes sense to me! It's always good to know I'm capable of understanding this sort of thing.
Oh and I'd like to know why a Student was silly enough to lick a newt.....let alone a very poisoinous one? Sounds like a story I'd like to hear. Also what does ETA mean?

Hehe. ETA means 'edited to add'.

Okay, story time

So, this was during a graduate recruitment drive, when lots of students come and visit different labs to see if they'd like to come. The professors and resident grad students are also checking out the new recruits to see if they'd be a good match.

Anyway, this particular guy was visiting the lab where they do the snake/newt work. He was convinced, based on a previous little study he'd done, that the newts don't make TTX on their own - they get it from their diet instead - so any newts held in captivity would be harmless. Well, the professor in the lab and the other grad students were absolutely sure that the newts in the lab, despite being in captivity for many years, were still very toxic.

So this guy feels he absolutely has to prove his point. He reaches into one of the newt tanks, grabs a big ol' fat Taricha from one of the most toxic populations, and - before anyone can stop him - gives it a big lick. Everyone's totally shocked and they all just stare at this guy, waiting for him to drop dead or at least get a little paralyzed: no one knows if a single lick is enough to kill someone.

After a few minutes, it's obvious that he's going to be fine. He's all happy because he thinks he just proved his point. The professor takes that particular newt and runs a test to see how much TTX it actually contains. It's absolutely loaded with TTX, thousands of times the amount needed to kill one grad student.

The key is that because the newt was so used to being handled, it wasn't overly upset about being grabbed and licked, so it just wasn't secreting any TTX. Needless to say, the guy didn't get into the lab.

So the moral of the story is: don't grab and lick a professor's newts

Funny story! While we're at it, sorry to press you with questions, what exactly is TTX made of, it's not a protien toxin (isn't that more in the venom of snakes...?) so what is it? Full of questions!

I believe it's an acid, but I'm not entirely sure - biochemistry wasn't my thing. Here's the wiki page on it, which has the molecular structure:

http://en.wikipedia.org/wiki/Tetrodotoxin

Erin, that story made my day! What a laugh!:ha:

I think I watched this documentary In Bio class, actually...

May i ask if anyone knows the name of the documentary? I´d love to see if i can find it.

I know the story is featured in the PBS series "Evolution", here's a clip of it - Drs. Brodie and Brodie out hunting for snakes (Warning: they make a snake puke):

http://www.youtube.com/watch?v=Xlkj-NoZyn0

eta: The snake/newt bit is featured in episode 4: "The Evolutionary Arms Race"

Hey,

I didn't find this link I read for my master-thesis so I just post it here. Maybe somebody else did before but mybe it's also new for you. It shows the evolution of the poison of the newts (Taricha granulosa) and the resistance evolution by the garter snakes. It shows the hotspots of this co-evolution. It occurs where the newts are the only prey of the snakes and it evolved twice: in the drier parts of Oregon and in central California. On Vancouver Island for example where the garter snakes have a greater variety of amphibian prey the newts are nearly non-toxic at all! I think this is a very interesting topic. Here you can find the paper!
I hope I showed you something new. Otherwise forget this post


Kind regards,

Marcus