Biologists from the University of California, San Diego report they have identified the cells and protein receptors responsible for sensing sour, one of the five basic tastes, and that the same receptor may work as a health monitor in the central nervous system.
According to the UCSD team, this finding and past research indicate each of the five basic tastes are detected by distinct receptors found in distinct cells in all areas of the tongue. This notion challenges the common view that different tastes are associated with specific parts of the tongue.
To determine if the cells and receptors for sour are distinct from those for the other basic tastes, the UCSD scientists tested mice in which they had genetically removed the cells containing the identified sour taste receptors. While the mice could not sense the sour taste, they had normal sweet, bitter, umami and salty tastes.
"Our results show that each of the five basic taste qualities is exquisitely segregated into different taste cells," explained Charles Zuker, Ph.D., a professor of biology at UCSD and a Howard Hughes Medical Institute investigator, who headed the study. "Taken together, our work has also shown that all taste qualities are found in all areas of the tongue, in contrast with the popular view that different tastes map to different areas of the tongue."
In addition to being found in the taste buds, the UCSD team found the sour protein receptor along the entire length of the spinal cord in nerve cells that reach into the central canal. Because sourness is a reflection of acidity, or pH, they contend the sour receptor may be responsible for monitoring the pH of the cerebrospinal fluid.
"There have been many claims for pH detectors that monitor the health of different body fluids, but the nature of the circuit and the receptors has been unknown," said Dr. Zuker. "Therefore it is significant to discover that the same protein that detects sour tastes also functions as a sentinel of pH in the central nervous system."
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