One of the most fascinating things to me is the fragile balance that our bodies seem to (mostly) maintain on a day to day basis. We tend not to think about it unless something goes wrong, but it’s always there, making sure the right signals reach the right parts of our body and have the right effect. Our bodies must be able to respond to certain stimuli and so we have an intricate communication system within our bodies to allow this. Both certain venomous snakes and Clostridium botulinum (the bacterium which produces the botulinum toxin – botox) have evolved a way of disrupting this system.
We all know that botox is a chemical which celebrities like to inject into themselves to make them look younger. But how does it “reverse ageing”? Long story short, it doesn’t; it just prevents muscle movements in the location where it is injected. It works by interfering with the processes which occur at a neuromuscular junction (the junction between a neurone and a muscle cell). Normally, the arrival of the action potential in the presynaptic terminal at the end of the neurone would stimulate voltage-gated calcium channels to open. The calcium binds to vesicles which hold acetylcholine, and in turn causes the vesicles to fuse with the membrane and release acetylcholine into the synapse between the neurone and the muscle. From there, acetylcholine binds to receptors on the muscle cell, triggering a chain of events inside the muscle cell which lead to muscle contractions.
Botox prevents the vesicles from fusing with the membrane by interfering with SNARE proteins which help the vesicles to bind, halting all of the events which follow on from this, preventing muscle contractions and therefore causing paralysis of the affected muscles, stopping people who have had botox from having their previous range of facial expressions, and smoothing out wrinkles. Tiny doses are administered for cosmetic purposes and this seems to be safe. However, it only requires a very small amount of the actual toxin to be lethal.
Some toxins found in venoms have exactly the same effect as botox – paralysis of muscles – but most interestingly, some have the opposite effect, yet can still result in the same unpleasant outcome. Some toxins found in certain snake venoms cause continuous contraction of muscle cells, rather than the inability to contract. Usually, after acetylcholine binds to receptors on the muscle cell, it is broken down by an enzyme called acetylcholinesterase. Certain snake venoms, containing fasciculins, which are common in mambas, destroy acetylcholinesterases so acetylcholine cannot be broken down. Acetylcholine keeps binding to the receptors, continuously stimulating the muscle cell to contract, leading to problems such as respiratory paralysis and can be followed by death.
Botox and the fasciculins in snake venom interact with different parts of one very small area, one preventing stimulation, and one causing overstimulation. The body is a delicate system; too much in either direction can have the same fatal result. It seems we are surrounded by things, that given enough dosage or enough time, could kill us, however harmless they may seem in the small amounts we encounter them in.
It’s that happy medium between droughts and flooding, only I’d never really thought of our bodies as having this kind of specificity. I mean, I knew that we could be hyperthermic, or hypothermic, hypoglycaemic or hyperglycaemic, but I’d rarely thought about applying that to a molecular level, where everything exists in minute concentrations. We pretty much just expect our bodies to deal with whatever we put in them. And for the most part, they really do an astonishing job.
Thank you for reading, comments and questions are always welcome!