Pain neurons have a couple of different sodium channels, called 1.7 and 1.8, and research has shown that when toxins bind to 1.7 channels, the channels open, sodium flows in and the pain neuron fires.
By sequencing the genes for both the 1.7 and 1.8 sodium channels, the scientists discovered that channel 1.8 in the grasshopper mice has amino acids different from mammals that are sensitive to bark scorpion stings, such as house mice, rats and humans. They then found that the scorpion toxin binds to one of these amino acids to block the activation of channel 1.8 and thus inhibit the pain response.
"Incredibly, there is one amino acid substitution that can totally alter the behavior of the toxin and block the channel," said Zakon.
The riddle hasn't been completely solved just yet, though, Rowe said.
"We know the region of the channel where this is taking place and the amino acids involved," she said. "But there's something else that's playing a role, and that's what I'm focusing on next."
Some resistance to prey toxins in mammals has been found in other species. The mongoose, for example, is resistant to the cobra. And naked mole rats' eyes do not burn in pain when carbon dioxide builds up in their underground tunnels.
This study, however, is the first to find that an amino acid substitution in sodium channel 1.8 can have an analgesic effect.
Rowe said studies such as this could someday help researchers target these sodium channels for the development of analgesic medications for humans.
|Contact: Ashlee Rowe|
University of Texas at Austin