The Science of Pain: Calcium Plays a New Role in Sensing Pain

Pain causes you to automatically react. For example, when you accidentally touch a hot stove, you rapidly pull your hand away. Now, scientists have uncovered a bit more about the role of pain; they've found a key molecule which may help direct new strategies to treat pain in people.

In humans and other mammals, a family of molecules called TRP ion channels play a crucial role in nerve cells that directly sense painful stimuli. In order to learn a bit more about these channels, the researchers turned to the roundworm Caenorhabditis elegans, which also expresses TRP channels-one of which is called OSM-9. OSM-9 is actually a functional match to TRPV4, which is a mammalian TRP channel involved in sensing pain.

The scientists created genetically modified worms that had parts of the OSM-9 channel either disabled or replaced. More specifically, the worms had alterations in the pore of the OSM-9 channels in their pain-sensing neuron, which gets fired up upon activation to allow calcium and sodium to flow through the neuron. This, in turn, was thought to turn on the neural circuit that encodes for rapid withdrawal behavior. Then, the researchers tested the worms' reaction to an overly salty solution, which is normally painful.

So what did they find? It turns out that changing bits of OSM-9's pore didn't change most of the mutant worms' reactions to the salty solution. What the mutations did do, though, was affect the flow of calcium into the cell. It's likely that this was because calcium wasn't playing a direct role in the worms' avoidance behaviors-surprising considering that calcium was thought to be indispensible for pain behavior.

"We assume, and so far the evidence is quite good, that chronic, pathological pain has to do with people's genetic switches in their sensory system set in the wrong way, long term," said Wolfgang Liedtke, one of the researchers, in a news release. "That's something our new worm model will now allow us to approach rationally by experimentation."

The findings are published in the journal Nature Communications.