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Discovery of Taste Receptors in the Lungs Could Help People With
Asthma Breathe Easier
http://www.sciencedaily.com/releases/2010/10/101024144132.htm
ScienceDaily (Oct. 25, 2010) — Taste receptors in the lungs?
Researchers at the University of Maryland School of Medicine in
Baltimore have discovered that bitter taste receptors are not just
located in the mouth but also in human lungs. What they learned about
the role of the receptors could revolutionize the treatment of asthma
and other obstructive lung diseases.
"The detection of functioning taste receptors on smooth muscle of the
bronchus in the lungs was so unexpected that we were at first quite
skeptical ourselves," says the study's senior author, Stephen B.
Liggett, M.D., professor of medicine and physiology at the University
of Maryland School of Medicine and director of its Cardiopulmonary
Genomics Program.
Dr. Liggett, a pulmonologist, says his team found the taste receptors
by accident, during an earlier, unrelated study of human lung muscle
receptors that regulate airway contraction and relaxation. The airways
are the pathways that move air in and out of the lungs, one of several
critical steps in the process of delivering oxygen to cells throughout
the body. In asthma, the smooth muscle airways contract or tighten,
impeding the flow of air, causing wheezing and shortness of breath.
The taste receptors in the lungs are the same as those on the tongue.
The tongue's receptors are clustered in taste buds, which send signals
to the brain. The researchers say that in the lung, the taste
receptors are not clustered in buds and do not send signals to the
brain, yet they respond to substances that have a bitter taste.
For the current study, Dr. Liggett's team exposed bitter-tasting
compounds to human and mouse airways, individual airway smooth muscle
cells, and to mice with asthma. The findings are published online in
Nature Medicine.
Most plant-based poisons are bitter, so the researchers thought the
purpose of the lung's taste receptors was similar to those in the
tongue -- to warn against poisons. "I initially thought the
bitter-taste receptors in the lungs would prompt a 'fight or flight'
response to a noxious inhalant, causing chest tightness and coughing
so you would leave the toxic environment, but that's not what we
found," says Dr. Liggett.
There are thousands of compounds that activate the body's bitter taste
receptors but are not toxic in appropriate doses. Many are synthetic
agents, developed for different purposes, and others come from natural
origins, such as certain vegetables, flowers, berries and trees.
The researchers tested a few standard bitter substances known to
activate these receptors. "It turns out that the bitter compounds
worked the opposite way from what we thought," says Dr. Liggett. "They
all opened the airway more profoundly than any known drug that we have
for treatment of asthma or chronic obstructive pulmonary disease
(COPD)." Dr. Liggett says this observation could have implications for
new therapies. "New drugs to treat asthma, emphysema or chronic
bronchitis are needed," he says. "This could replace or enhance what
is now in use, and represents a completely new approach."
Quinine and chloroquine have been used to treat completely different
diseases (such as malaria), but are also very bitter. Both of these
compounds opened contracted airways profoundly in laboratory models.
Even saccharin, which has a bitter aftertaste, was effective at
stimulating these receptors. The researchers also found that
administration of an aerosolized form of bitter substances relaxed the
airways in a mouse model of asthma, showing that they could
potentially be an effective treatment for this disease.
Dr. Liggett cautions that eating bitter tasting foods or compounds
would not help in the treatment of asthma. "Based on our research, we
think that the best drugs would be chemical modifications of bitter
compounds, which would be aerosolized and then inhaled into the lungs
with an inhaler," he says.
Another paradoxical aspect of their discovery is the unexpected role
that the mineral calcium plays when the lung's taste receptors are
activated. The study's principal author, Deepak A. Deshpande, Ph.D.,
assistant professor of medicine at the University of Maryland School
of Medicine, is an expert in how calcium controls muscles. "We always
assumed that increased calcium in the smooth muscle cell caused it to
contract, but we found that bitter compounds increase calcium and
cause relaxation of airway muscle in a unique way," says Dr.
Deshpande. "It appears that these taste receptors are wired to a
special pool of calcium that is right at the edge of these cells," he
says.
"The work of this team exemplifies what it takes to make real
improvements in treating certain diseases," says E. Albert Reece,
M.D., Ph.D., M.B.A., vice president for medical affairs at the
University of Maryland and dean of the University of Maryland School
of Medicine. "These researchers were willing to take chances and ask
questions about an unlikely concept. Why are taste receptors in the
lungs? What do they do? Can we take advantage of them to devise a new
therapy? In the end, their discoveries are in the best tradition of
scientific research."
Editor's Note: This article is not intended to provide medical advice,
diagnosis or treatment.
Story Source:
The above story is reprinted (with editorial adaptations by
ScienceDaily staff) from materials provided by University of Maryland
Medical Center, via EurekAlert!, a service of AAAS.
Journal Reference:
1. Deepak A Deshpande, Wayne C H Wang, Elizabeth L McIlmoyle,
Kathryn S Robinett, Rachel M Schillinger, Steven S An, James S K Sham,
Stephen B Liggett. Bitter taste receptors on airway smooth muscle
bronchodilate by localized calcium signaling and reverse obstruction.
Nature Medicine, 2010; DOI: 10.1038/nm.2237
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"Ethics" is simply a last-gasp attempt by deist conservatives and
orthodox dogmatics to keep humanity in ignorance and obscurantism,
through the well tried fermentation of fear, the fear of science and
new technologies.
There is nothing glorious about what our ancestors call history,
it is simply a succession of mistakes, intolerances and violations.
On the contrary, let us embrace Science and the new technologies
unfettered, for it is these which will liberate mankind from the
myth of god, and free us from our age old fears, from disease,
death and the sweat of labour.
Rael
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