Electrogenic humansMonday, 13 October, 2008
Electrogenesis refers to the production of electrical activity in living tissue. In a sense, we humans are already electrogenic; each of our brain cells (neurons) produces about 70 millivolts of electric potential and our muscle cells about 95 millivolts. They do this by using chemical energy (in the form of ATP) to power electrogenic pumps, most commonly the Na+/K+ ATPase (sodium-potassium transporter, but usually abbreviated to NAKA)- this enzyme is so common in the massive human brain and muscles that it is responsible for using up to 40% of our resting energy consumption (and the man who discovered it, Jens Skou, was awarded the 1997 Nobel Prize in Chemistry. This pumps out 3 Na+ atoms in exchange for 2 K+ atoms. This is a good deal, because three positively charged ions (cations) are exchanged for two, which causes the electric potential to drop below zero. With enough of these going, it will drop give the cell a slight charge.
But some marine creatures really excel in this aspect, with specialised cells called electrocytes dedicated entirely to the production of an electric potential, which they use primarily to communicate and sense prey but also to stun other animals (prey or predators). These include the electric rays (Torpediniformes) which can produce a potential of around 200 volts, the electric catfish (Malapteruridae) which are capable of producing 350 volts and, perhaps one the best known (erroneously as the electric eel), the electric knifefish (Electrophorus electricus), capable of a shock of up to 600 volts (Mermelstein et al, 2000). The electric knifefish/eel has been proposed as next on the list of animals to have their genome sequenced (Albert et al, 2008), which I think will speed this sort of research along quite nicely.
These animals have a specialised organ, called (of all things) the electric organ, which is made up of thousands of these electrocytes (sometimes also called electroplaques or electroplaxes) organised in series (with each series stacked in parallel to sum currents), with each cell producing a potential about 150mV (actually, there are two potentials, one 65mV and the other 85mV. For details, read Jian Xu’s scientific paper, which I link to below). That doesn’t seem like much, but stack ten thousand of these in one organ and, if all those cells discharge at one, it will produce a 1500V electric organ discharge (EOD).
Just last month, researchers Jian Xu from Yale University and David Lavan from the National Institute of Standards and Technology (Maryland, USA) published a paper in Nature Nanotechnology outlining a theoretical upgrade to the electrocyte, able to produce 28% more power and to use chemical energy to do it with 38% greater efficiency. It was theoretical, however, but they will probably try it (or somebody else will) for real some time soon. And probably the electric fishes themselves will be slowly evolving towards this outcome themselves.
In the meantime, we can consider how awesome it would be to generate an electric current ourselves. Most in the Western world are experiencing an obesity epidemic, so we have plenty of chemical energy to spare for producing an electric potential. The most likely and practical option will be to have a small patch of electrogenic cells surrounding any electronic implant, like the prosthetic arm and cybernetic implants we will all have by that stage. They may also prove useful in biological pacemakers, if the heart was surrounded with electrogenic cells to provide impulses (though, it would probably prove easier to just repair the heart).
More interestingly (at least in my opinion), we could genetically engineer (or implant) our very own electric organ. If the electric organ was just below the skin of our chest and arms, but very well insulated except for at ends of our fingers, we’d literally have the full current and voltage of the electric organ at our fingertips. We’d also need to wire up the brain control mechanisms of this organ, specifically some brainstem nucleus to act as a pacemaker to ensure all those electrocytes fire together, so that we could control when the electric shocks occur.
Now, before we get all excited about throwing lightning bolts, let me first remind everyone of how physics works back in the real world. As I said, bioelectrogenesis has evolved only in aquatic organisms, because water is a good conductor. Air, on the other hand, is a damn good insulator until a phenomena known as dielectric breakdown occurs (this is when the air ionises to become conductive). The dielectric strength of air is 3,000,000 volts per metre (3MV/m), but greater on hot or humid days. This means that to throw an arc discharge (i.e. a zap of lightning) across on metre of air, you require 3 million volts. You can throw a much smaller arc with much less, as anyone who as zapped themselves with static electricity on a doorknob will know (noting Paschen’s law, which shows that even a small voltage of 500V will be sufficient to cross a gap of half a centimetre). If I hold my thumb and forefinger just a centimetre apart, I will still require 30,000 volts to throw an arc between them. To produce that with a current of 1 amp (which probably won’t be necessary, but let’s assume that for the sake of ease of calculation) would require about 150,000 cells (assuming each produces 200mV), which is far more than the electric eel has (and, mind you, the electric eel dedicates about 80% of its 25kg body to its electric organs, and still only manages about 4000 cells per series). So in other words, you’re not going to be able to throw lightning (which makes sense, because we don’t even have a practical ‘lightning gun‘ yet, let alone a biological version).
But I don’t really care. I’d settle for being able to make a lightbulb glow or give somebody an annoying shock if they irritated me (essentially a biological electroschock weapon). So, where’s my bioelectrogenesis?
[Hat tip to fayyaad at Utter Insanity for inspiring me to try to explain how human electrogeneration is possible and bringing my attention to this recent news]