Like teenagers, cells in our bodies constantly chatter back and forth. But instead of zapping text messages, they relay signals with molecules. Now, researchers have discovered a surprisingly tiny new messenger in worms: protons. The find raises the possibility that the subatomic particle plays the same role in humans, the researchers say.
Research in mice has hinted that protons--hydrogen atoms stripped of their electrons--might act as messengers, but until now direct evidence has been lacking. A team led by biologist Erik Jorgensen of the University of Utah, Salt Lake City, made the discovery while investigating how the worm Caenorhabditis elegans contracts certain muscles around its intestines to squeeze out waste. Previous experiments had ruled out several neurotransmitters known to aid defecation, suggesting that a novel molecule might be playing a role.
After sequencing the DNA of worms with defects in muscle contraction, the team identified mutations in a gene called PBO4. This gene encodes a protein located on the outer surface of intestinal cells, where it brings sodium ions into the cell while pumping protons out. This hinted that protons might play a role in making the muscles contract.
Next, using a protein that glows green until it contacts protons, the researchers found that protons flood from the intestinal cells and into the surrounding muscle cells just before the muscle contracts. Finally, the researchers inserted protons bound to a light-sensitive molecule into the space between the intestine and the muscle in mutant worms with a defective PBO4 gene. When a flash of light set the protons free, the muscle contracted, the researchers report in the 11 January issue of Cell. Further experiments identified a receptor on the muscle cells that triggers contraction when protons bind to it.
Jorgensen speculates that protons probably act as neurotransmitters in humans and other vertebrates, but so far there is no evidence of this. He notes that this could explain why humans have proton pumps in brain cells that are the same as the proton pumps found in their intestines.
Les Iversen, a neuroscientist at the University of Oxford, U.K., agrees with that notion. But Charles Stevens, a neurobiologist at the Salk Institute for Biological Studies in San Diego, California, says that the protons may only be used as neurotransmitters in worms and other invertebrates. "Oftentimes, invertebrates have evolved special mechanisms that are not so widely used in vertebrates," Stevens says.