EMBARGOED UNTIL MARCH 4, 2008
Contact: Donna Krupa
Office: (301) 634-7209
dkrupa@the-aps.org
Specialized Nasal Sensory Cells Detect Irritants In The
Environment
Researchers discover a new cell function inside the
nasal cavity
BETHESDA, Md. — Many chemicals, including most odorants in highly
concentrated form, are irritating to the nose and can cause burning,
stinging, warmth, itching or pain. The sensations occur when high levels of
the chemical odors activate the trigeminal sensory system in the nasal
cavity. The sensations are a signal of poor air quality and potential heath
risks.
It is not yet known how the initial process occurs but a small, important
step towards understanding it has been made. A team of researchers have
discovered that specialized receptor cells of the upper nasal cavity respond
to a broad array of chemical irritants including odorants at high
concentrations. These cells allow an animal to quickly monitor and avoid
potentially irritating and toxic compounds in the environments.
The Study
The authors of the study, “TRPM5-expressing Solitary Chemosensory Cells
Respond to Odorous Irritants” are Weihong Lin and Tatsuya Ogura, Department
of Biological Sciences, University of Maryland, Baltimore County, MD; Robert
F. Margolskee, Department of Neuroscience, Mount Sinai School of Medicine,
New York, NY; and Thomas E. Finger and Diego Restrepo, Department of Cell
and Developmental Biology, The Neuroscience Program, and Rocky Mountain
Taste and Smell Center, University of Colorado Denver School of Medicine,
Aurora, CO. Their findings appear in the March 2008 edition of the
Journal of Neurophysiology, (doi:10.1152/jn.01195.2007), a publication
of the American Physiological Society (APS;
http://www.the-aps.org/).
Background
Solitary chemosensory cells (also called “solitary chemoreceptor cells”)
affecting the trigeminal nerve were first identified in the nasal cavity of
rodents with an antibody against α-gustducin (a protein found in taste
receptor cells). A broader class of chemosensory cells expressing the
transient receptor potential ion channel M5 (TRPM5) within the airway and
gastrointestinal tract has also been identified.
Summary of Methodology and Findings
This research was designed to investigate nasal TRPM5-expressing cells
and their chemical responsiveness to volatile irritants. Histological
analysis of TRPM5-GFP (green fluorescent protein) transgenic mice showed the
presence of over 5,000 sensory cells on each side of the nasal cavity
demonstrating the significance of this sensory modality.
Functional studies of the TRPM5-expressing solitary chemosensory cells
with a technique to image intracellular Ca2+ levels showed that
these cells respond to many different odorous chemicals at a high
concentration. Previously it was thought that only olfactory sensory
neurons (for the sense of smell) detect odorous molecules. Yet olfactory
responses would not account for the irritating quality of odorants at high
concentrations. Thus the current study provides a mechanism for our
sensitivity to a broad array of chemical irritants.
Conclusions
This is the first direct demonstration that TRPM5-expressing solitary
chemosensory cells in the nasal cavity respond to odorous chemical irritants.
This is an example of the Law of Specific Nerve Energies (Johannes Peter Müller:
1826) who said that the quality of a perception is not dictated by the physical
nature of the stimulus, but rather by the perceptual apparatus or sensory nerve
conveying the information. The classic example is that if you sit in a dark
place, close your eyes to adapt to the dark, and then push gently on the
eyeball, you would perceive a blob of light even
though the stimulus is mechanical pressure.
Similarly, here in this system, an odorant is not perceived as being, e.g.
flowery, but rather is perceived as an irritant at high concentrations because
the information is transmitted via the trigeminal nerve. According to Dr. Lin,
the first author of the study, “We have discovered a new cell function that we
did not know existed. These findings bring
us a step closer to understanding the way in which certain cells inside the nose
protect us from potential harm.”
-end-
Physiology is the study of how molecules, cells, tissues and organs
function to create health or disease. The American Physiological Society
(APS;
http://www.the-aps.org/ has been an integral part of the scientific
discovery process since it was established in 1887.
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NOTE TO EDITORS: To schedule an interview with Dr. Lin, please
contact Donna Krupa at 301.634.7209 (direct dial) or
DKrupa@The-APS.org.
Key words: solitary chemosensory cells (SCC); nasal irritant;
American Physiological Society; APS
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