The study, featured on the cover of the August 24 issue of the journal
Nature, reports that each of the five basic tastes is detected by
distinct taste receptors—proteins that detect taste molecules—in
distinct cells. The team previously discovered the sweet, bitter and
umami (savory) receptors and showed that they are found in separate
cells, but some researchers have argued that sour and salty tastes,
which depend on the detection of ions, would not be wired in the same
way.
“Our results show that each of the five basic taste qualities is
exquisitely segregated into different taste cells” explained Charles
Zuker, 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.”
To determine if the taste cells and receptors for sour were separate
from the receptors for the other basic tastes, the researchers tested
mice in which they had genetically ablated the cells containing the sour
taste receptors. The mice could not taste sour, but had completely
normal sweet, bitter, umami and salty tastes. Therefore, although the
salt taste receptor has not yet been discovered, it and the four
identified receptors must each be segregated into distinct taste cells.
In addition to being found in the taste buds, the researchers discovered
that the sour protein receptor, PKD2L1, is also found along the entire
length of the spinal cord in nerve cells that surround and reach into
the central canal. Because sourness is a reflection of the acidity, or
the pH of a solution, the researchers suspected that the spinal neurons
with PKD2L1 might be responsible for monitoring the pH of the
cerebrospinal fluid.
http://www.sciencedaily.com/releases...0823184824.htm
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