Julius, professor and vice-chair of the Department of Cellular and Molecular Pharmacology at the University of California, San Francisco, explained that the TRPA1 is like a door on a cell's surface. When something causes it to open, electrically charged atoms can enter the cell's interior.
To see if garlic affected this channel, Julius and his team performed experiments with garlic itself and allicin, an organic compound containing sulfur that is present in garlic. They tested how rat cells reacted to allicin and garlic's other sulfurous ingredients, but they say humans likely would react in a similar way.
The findings are published in the current Proceedings of the National Academy of Sciences.
The scientists determined that allicin and garlic's other potent compounds first bind to protein receptors on the surface of nerve endings on the tongue and other parts of the mouth. This causes the TRPA1 ion channel to open, allowing ions such as sodium and calcium to rush into the nerve cell.
"When this occurs, an electrical signal is generated and sent to the spinal cord, and from there to pain processing centers of the brain," Julius said. "This produces a sensation of discomfort or pain. At the same time, the sensory nerve fiber releases substances at the initial site of activation (in the mouth), causing vasodilation and inflammation in the surrounding tissue."
The researchers performed related studies on the potent compounds found in chili peppers and mustards like yellow mustard and wasabi. They found that the body reacts to these ingredients in a similar way. This suggests chilis and mustards might also lower blood pressure.
David Clapham, professor of neurobiology at the Harvard Medical School and a researcher at the Howard Hughes Medical Institute, told Discovery News that he agrees with the study. He attributes the potency of garlic, chilis and mustard to natural plant defense mechanisms.
Clapham said, "In the long coevolution with animals, plants make molecules that attract — smell or taste good — for help in spreading their seeds, or repel animals — taste bad, etc. — to keep from being eaten."
Michael Caterina, associate professor of biological chemistry at the Johns Hopkins School of Medicine, also agrees with the new research, but he thinks further studies are needed before diners should load up on garlic, chilis and mustard for health reasons.
"This study should be viewed as a fascinating step towards scientific understanding of the ways in which plant-derived chemicals can interact with proteins in our bodies, but not as a basis for canceling your gym membership and planting a quarter-acre of garlic in your back yard," Caterina told Discovery News.
He added, "Spicy foods should be enjoyed for their taste and the company with which they are shared. In time they might also prove to be important components in a healthy diet, but right now, that's not entirely clear."
