Electric fish are some of the most extraordinary creatures that live on this planet, and while ghost knifefish might not be the most deadly of these bright sparks, they do set their own records. They can discharge electricity at frequencies of over 1,000 pulses per second, creating action potentials along their cells quicker than any other animal in the world.
The fish are able to make the electric pulses using a set of modified motor neurons in the spinal cord, which form part of an electric organ that generates the pulses of electricity. These are generated thanks to sodium channels in the cell membranes. The tiny pores allow positively charged sodium ions in and out of the cell in a regulated fashion, creating an action potential that pulses along the length of specific cells to either send a message or, in the case of muscle cells, make the cells contract.
One type of sodium channel is known as a “voltage-gated” channel, which opens and closes in response to a change in voltage along the cell membrane and is usually only found in muscle tissue. Ghost knifefish, it turns out, can attain the highest frequency action potential of any cell type in any animal by using these modified voltage-gated channels.
In other words, they send a pulse down the neurons at a rate faster than an incredible 1,000 pulses per second (1 kilohertz). Not only that, but they can do it spontaneously without any input from the brain. Now, a new PLOS Biology study has revealed the genetics behind this ability.
To figure out how the fish manage this, researchers turned to their genes. By comparing the genome of the electric fish to other non-electric fish, they were able to pinpoint what changes were occurring to allow the channels to fire so rapidly.
They found that the gene that codes for the voltage-gated sodium channels in muscle cells duplicated itself in ghost knifefish some 14.5 million years ago. But in addition to that, around 2 million years ago a mutation in these genes meant the channels were not only being expressed in muscle cells but also in the motor neurons of the spinal cord, which now form part of the electric organ that dictates the firing frequency.
The mutations didn’t stop there, though. Further alterations to the genes meant that these sodium channels, now being produced by cells that ordinarily don’t make them, were able to open and close at a much quicker frequency than their ancestral muscle channels. This all combined to make ghost knifefish the record-breakers they are now.
You might think that this is all abstract knowledge of little importance, but the researchers hope to use the information to give insights into the genetic basis of conditions such as epilepsy, or other inherited diseases that cause muscle weakness.