Deep in the night in muddy African rivers, a fish uses electrical charges to sense the world around it and to communicate with other members of its species. Signaling in electrical spurts – that a few tenths of a thousandth of a second – allows the fish to navigate without letting predators know it is there.
Now, scientists led by a team at Michigan State University and the University of Texas at Austin discovered that the evolutionary trick these fish use to make electrical discharges could provide new insights, with a bearing on treatments for diseases like epilepsy.
These findings, published in Current Biology, outline how some fish, commonly referred to as baby whales, have developed the ability to produce fast and short pulses of electricity to communicate without jamming one another’s signals. At the same time, these pulses serve as a highly sensitive electric detection systems of predatory catfish.
“These fish have a real ‘need for speed’ when it comes to their electric signals,” said Jason Gallant, assistant professor of integrative biology at MSU and a researcher on the project. “Many of the genes involved in making electric discharge signals, including these potassium channels, show signatures of natural selection that emphasize this need.”
In a specialized electric organ near the tail, these weakly electric fish possess a protein that also exists in the hearts and muscles of humans. The electrical pulses generated through this protein, called the KCNA7 potassium ion channel, last just a few tenths of a thousandth of a second. In fact, some electric fish have adapted to learn the timing differences in electrical discharges of less than 10 millionths of a second.
“Most fish cannot detect electric fields, but catfish sense them. The briefer electric fish can make their electric pulse, the more difficult it is for catfish to track them,” said Harold Zakon, a professor in the UT Austin Departments of Integrative Biology and Neuroscience.
The team identified a negatively charged patch in the KCNA7 protein that allows the channel in the electric fish to open quickly and be more sensitive to voltage, allowing for the extremely brief discharges.
What scientists have learned about these fish, their electrical signals and how they evolved may help humans in the future by shedding light on how those same electrical pathways operate in conditions such as epilepsy, where electrical pulses in the brain and muscles cause seizures. The finding also may have implications for discoveries about migraines and some heart conditions.
“Mutations in potassium channels that make them too sensitive or not sensitive enough to electrical stimuli can lead to epilepsy or cardiac and muscle diseases,” said Swapna Immani, first author of the paper and a UT Austin research associate in neuroscience and integrative biology. “So understanding what controls the sensitivity of potassium channels to stimuli is important for health as well as a basic understanding of ion channels.”
Previous understanding of the same protein was based on potassium channels in fruit flies, but the MSU and UT Austin researchers say this paper suggests that the particular region with the negative patch might function differently in vertebrates.
Looking at the evolution of the specialized electric organ also can provide important windows into how genes change and express themselves. By studying unique or extreme abilities in the animal kingdom, much can be learned about the genetic basis of adaptations, the paper said.
“The take-home message of our project is that strange animals such as weakly electric fish can give very deep insights into nature, sometimes with important biomedical consequences,” Gallant said. “We discovered something at first blush that would seem like an idiosyncrasy of the biology of electric fish, which is always exciting but lacks broad applicability. Because of the relaxed evolutionary constraints on this important potassium channel in electric fish, which don't have to follow the same rules normally imposed by nervous system or muscle, the tinkering of natural selection has revealed a physical 'rule' that we suspect governs potassium channels more broadly."
Funding for the research came from the National Science Foundation and the National Institutes of Health.