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The human body is packed with electricity. In fact, just 20 human neurons connected end to end can deliver the same voltage as an AAA battery. And since there are somewhere between 10 billion and 1 trillion neurons in the average human brain, try to imagine the mountain of AAAs it would take to match your potential output.
All this electrical life is due to ion channels. “If you can think of a cell as a kind of integrated circuit, then an ion channel would be a transistor,” says HHMI investigator David E. Clapham. “It's a switch that opens and closes and allows an electrical charge to permeate down a chemical gradient in the cell.”
Researchers knew as far back as the 1700s that electrical activity occurred in our bodies. But it wasn't until the 1950s that Allen Hodgkin and Andrew Huxley discovered that ion channels selected for particular ions, such as sodium, calcium, and potassium—work that earned them a Nobel Prize in 1963.
“Electrical activity in cells is used for many reasons,” explains Clapham. “All nervous activity depends on ion channels. One nerve can't communicate to another without them. When your heart beats or when your muscles contract, ion channels are involved in all the signaling that's going on.”
Nature has also stumbled upon many other ways to exploit ion channels. For example, the eel can aggregate billions of ion channels into a single assault weapon and electrocute its prey.
Ion channels can be the target of an attack as well. Take the pufferfish, widely considered a delicacy in Japan and Korea. Every once in a while, an unsuspecting restaurant patron just finishing a meal of pufferfish loses the ability to breathe. This alarming state occurs because a venom found in the fish's internal organs, called tetrodotoxin, can disable sodium ion channels throughout the body of a victim (whether human diner or natural predator), making it impossible for nerve cells to signal each other. The result can be fatal if enough toxin is ingested.
“Most toxins in nature work like this,” says Clapham. “It's a good way for one animal to affect another one quickly.”