Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers identify the cells and receptor for sensing sour taste

25.08.2006
In the last seven years, Howard Hughes Medical Institute researcher Charles S. Zuker and Nicholas J.P. Ryba at the National Institutes of Health have worked together to identify the cells, receptors and signaling mechanisms for three of the five tastes humans can sense -- sweet, bitter, and umami (the taste of monosodium glutamate).

Now, Zuker, Ryba, and their team of researchers have identified the cells and the receptor responsible for sour taste, the primary gateway in all mammals for the detection of spoiled and unripe food sources.

The receptor is found in a subpopulation of taste receptor cells of the tongue that do not function in sweet, bitter, or umami taste, the researchers report in the August 24, 2006, issue of the journal Nature.

This finding is "very satisfying," said Zuker, "because it seals the case that we had built before with sweet, bitter, and umami, showing that each taste is mediated by fully dedicated sensors." A contrasting view held that individual tongue cells detect more than one taste modality, with the quality of the taste being encoded in a complicated pattern of nerve signals sent to the brain.

The hunt for the sour receptor began with a search of DNA and protein sequence databases. Angela Huang, a graduate student in Zuker's lab at the University of California, San Diego, and the lead author of the paper, screened the mouse genome for all of the genes encoding proteins that have transmembrane domains -- sections of the protein that allow the protein to be located in cell membranes.

"That screen narrowed the list significantly, from 30,000 to about 10,000," Huang said. She then used what Zuker calls "a stroke of ingenuity" to reduce the list further. Proteins that could detect sour compounds are likely to be found only in small numbers of tissues, including taste cells in the tongue. Huang therefore eliminated from the list all those proteins that are expressed in many different tissues. "That got it down to about 900 candidates," she said.

Huang then used a technique called reverse transcriptase polymerase chain reaction (RT-PCR) to find which of the candidates were expressed specifically in taste receptor cells. Of the approximately 30 proteins identified through RT-PCR, Huang searched for genes that were expressed in a small population of taste receptor cells -- the pattern that Zuker's and Ryba's team had previously discovered with taste receptors for sweet, bitter, and umami.

The researchers' attention was drawn immediately to a receptor molecule known as PKD2L1, which is related to a large family of proteins that shuttle ions into and out of cells. As predicted for a candidate sour receptor, PKD2L1 was not found in the cells that express the receptors for sweet, bitter, and umami, but instead was found in a novel population of taste cells. "Our fundamental premise was that salt and sour were going to be mediated by dedicated cells," said Zuker, "and those candidate receptors should not be present in sweet-, bitter-, or umami-sensing cells."

To link the receptors with the taste of sour, Zuker and his colleagues turned to another clever experimental strategy. Using a special mouse strain, they created genetically engineered mice that produced a diphtheria toxin in cells that expressed PKD2L1, thus killing the cells. They then recorded the nerve signals and tongue function coming from taste cells in the genetically-engineered mice. Remarkably, no matter what sour compounds they fed the mice, nerve signals from the taste cells remained absent; the animals were completely insensitive to all kinds of acids. But these "sourless" mice continued to be able to taste sweet, bitter, umami, and salt. "Killing these cells and showing that the mice now are totally unable to detect sour proved that these cells are the sensors for sour taste, and that indeed no other taste cells detect sour," said Zuker.

In an interesting extension of this work on taste, the investigators then examined whether cells expressing the sour receptor might be found anywhere else in the body, perhaps where sensing acidity might be important. They looked for the receptor in a large number of other tissues and discovered that it is expressed in a particular set of neurons surrounding the central canal of the spinal cord. Suspecting that these cells might be responsible for monitoring the level of acidity in the cerebrospinal fluid (CSF), the researchers recorded nerve signals from the cells in a slice of spinal cord tissue. When the surrounding solution turned acid, the cells became activated selectively, and immediately began firing nerve signals much more rapidly than when the solution was neutral or basic.

Discovery of the sour (acid) receptor in the central nervous system could help explain how the body monitors the quality of critical body fluids, Zuker said. For example, the body controls respiration in part by monitoring the acidity of the blood, since an increase in carbon dioxide dissolved in the blood increases acidity. "Defects in these blood-, CSF-, and brain-fluid-sensing systems may underlie a wide range of disorders," said Zuker.

Several intriguing questions can be pursued now that the sour-taste cells and candidate receptor have been found. One is how the PKD2L1 receptor is activated by acid stimuli. Another concerns the role of the neurons that innervate the central canal. And as Zuker pointed out, "This work also proved that salt-sensing cells, just like those mediating sweet, bitter, umami and sour, must function as independent sensors because the "sourless mice" have perfectly normal salt perception," he said. "So this opens an exciting experimental platform to molecularly dissect the last of the five basic taste qualities: salt taste."

Jim Keeley | EurekAlert!
Further information:
http://www.hhmi.org

More articles from Life Sciences:

nachricht For a chimpanzee, one good turn deserves another
27.06.2017 | Max-Planck-Institut für Mathematik in den Naturwissenschaften (MPIMIS)

nachricht New method to rapidly map the 'social networks' of proteins
27.06.2017 | Salk Institute

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Touch Displays WAY-AX and WAY-DX by WayCon

27.06.2017 | Power and Electrical Engineering

Drones that drive

27.06.2017 | Information Technology

Ultra-compact phase modulators based on graphene plasmons

27.06.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>