The highvelds, though, didn’t even flinch. So the researchers upped the dose, giving them pure AITC. (The lab member in charge of these injections, Karlein Debus, had to wear a gas mask.) “They had no reaction whatsoever,” said Dr. Lewin. “That was astonishing.”
Why don’t highvelds feel the burn? Dr. Lewin and his colleagues compared the pain-signaling neurons of the species included in the study. They found that neurons in the highveld mole-rat are uniquely riddled with a type of ion channel called NALCN. This channel is “leaky,” which “makes it harder to excite the neurons,” said Dr. Lewin.
They gave the highveld mole rats a drug that blocks this channel. This time, the AITC injections clearly bothered them. But about a day later, after the drug wore off, the mole rats were once again unruffled. “We could make them transiently sensitive,” said Dr. Lewin.
One mystery remained. Why did highveld mole rats evolve this defense? The answer came from Daniel Hart, a postdoctoral student at the University of Pretoria. Dr. Hart has been studying various mole rats for years, and noticed that whenever he reached into a highveld burrow, “I was always being attacked by ants.”
The ants in question, Natal droptails, have a nasty sting. Their venom likely contains formic acid, which is known from previous experiments to work like AITC. “The highveld mole rat has learned, over millions of years, to adapt to these ants” by cross hatching their neurons with leaky channels, said Dr. Lewin. Having developed this immunity, they can live where other mole rats fear to tread.
The discovery of the effect of these overexpressed channels “shows the potential for using drugs to modulate NALCN activity to treat pain in humans,” said Dr. Smith.
Plus, it’s another surprise from the prolific mole rat family: “It’s something that never would have occurred to me,” Dr. Lewin said.