Shocking outcome: mutation lets knifefish pack a punch
A relative of the electric eel is nature’s current favourite. Tanya Loos reports.
An unassuming fish from South America has the ability to deliver fast and powerful electric shocks, without even using its brain.
Members of an order called Gymnotiformes, or knifefishes, communicate with one another and sense their environment using weak electrical impulses generated by the muscles. The order contains the electric eel, which, despite its name, isn’t an eel at all.
A new study, published in the journal PLOS Biology, reveals that one family within the order, the Apteronotids, or “ghost knifefish”, use a completely different biological mechanism to generate the electrical signals – their spinal cords.
Ammon Thompson from the University of Texas, US, and colleagues reveal that these signals pack quite a punch. The researchers clocked one species of ghost knifefish (Parapteronotus hasemani) pumping out an eye-watering 1000 pulses per second, or one kilohertz, giving it the highest frequency action potential of any cell type, in any animal.
The fishes’ talent is due to a unique genetic rewiring, producing sodium channels in their spinal cords. Thompson’s team shows that the modified channels could contribute to the electric organ’s high-frequency firing.
Sodium channels are tiny pores in cells, involved in the generation of electrical signals to regulate cellular functions such as muscle contraction. One type, known as a “voltage-gated” channel, opens and closes in response to a current passing across the cell membrane.
In Apteronotids the gene that codes for voltage-gated channels in muscles has been duplicated, with the second version giving the fish the ability to make sodium channels in the spinal cord, resulting in modified motor neurons that regulate the firing frequency of the electric organ.
The duplicated gene, accumulating mutations over evolutionary time, also causes the spinal cord sodium channels to open and close more frequently than the ones in muscles, potentially explaining the big punch of the electric shock delivered.
It is the first time a sodium channel has been found anywhere other than in muscle tissue, and the discovery has implications for medical research. In humans, neurotoxin activity in muscle sodium channels is known to be a factor in several disorders. Studying the mutations involved in the knifefish could shed new light on the mechanisms involved.
The ghost knifefish has also attracted attention as a model in the field of robotics, based on its undulating fins. Its famous relative, the electric eel, is being studied as an inspiration for gel-based power generation.