Givaudan-Roure Lecture - Association for Chemoreception Sciences

185 Poster [ ] Functional Organization of the Gustatory
System
TASTE RESPONSE AND MOLECULAR EXPRESSION OF
RECEPTOR CELLS OF THE MOUSE FUNGIFORM PAPILLAE
Yoshida R. 1, Sanematsu K. 1, Ninomiya Y. 1 1Kyushu University,
Fukuoka, Japan
In taste bud cells, expression of various molecules concerned in taste
reception was detected by various molecular biological techniques.
Here, we investigated taste responses of receptor cells showing action
potentials and mRNA expression of taste related genes in these cells at
the same time. Using loose patch technique, we recorded increases in
firing frequency from taste bud cells tested for taste stimuli (NaCl,
Saccharin, HCl, Quinine HCl). Two types of NaCl responding cells
exist: one is amiloride-sensitive and the other amiloride-insensitive. In
some cells, responses to MSG were enhanced when MSG was mixed
with IMP. Responses to sweet substances in some receptor cells were
suppressed by apical treatment of gurmarin and recovered after apical
application of β-cyclodextrin. Of 68 cells responding to taste stimuli, 40
(59%) responded to one, 24 (35%) to two, and 4 (6%) to three of four
taste stimuli. The entropy value presenting the breadth of
responsiveness was 0.213 ± 0.252, which was close to that for the nerve
fibers. These results suggest that taste cells generating action potentials
have response characteristics to taste stimuli that are comparable to
those for nerve fibers. After recording of taste response, single receptor
cell was withdrawn from a taste bud and checked mRNA expression of
taste related genes such as T1R3 by RT-PCR method. Our preliminary
data indicate that a taste cell responding to sweet stimuli expressed
T1R3 and gustducin mRNA. Thus, this technique might be useful to
examine molecular expression in receptor cells responding to taste
stimuli.
186 Poster [ ] Functional Organization of the Gustatory
System
THE A BLOOD GROUP ANTIGEN IS EXPRESSED BY A
UNIQUE SUBSET OF TASTE BUD CELLS
Christy R.C. 1, Boughter J.D. 1, Smith D.V. 1 1Anatomy & Neurobiology,
University of Tennessee Health Science Center, Memphis, TN
Although mammalian taste cell types differ across species, most
investigators recognize at least two classes of elongated, spindle-shaped
cells: Type I (dark) and Type II (light) cells, based on their relative
electron densities when stained with uranyl acetate. These cell types
differ markedly in their morphology in transverse sections through the
taste bud. A third cell type (Type III), which is electron lucent and
round in transverse section like a Type II cell (and therefore a subtype
of “light” cell), was first described in rabbit foliate taste buds as
possessing synaptic connections with nerve fibers. Type III cells have
also been described in rat and mouse vallate taste buds on the basis of
specific antigen expression and ultrastructural similarity to rabbit Type
III cells. Here we examine rat and mouse taste buds for
immunocytochemical expression of several markers that delineate
differences among light cell types, which, unlike Type I cells, are
heterogeneous in their expression patterns. NCAM is expressed on a
subset of Type III cells and α-gustducin on a subset of Type II cells,
only some of which also express the Lewisb blood group antigen. The
blood group A antigen co-localizes with α-gustducin on some cells
(which do not express Lewisb ) and not others but does not label any
NCAM- or PGP 9.5-positive cells. Combined with the work of others
showing subtypes of Type III cells expressing combinations of PGP
9.5, 5-HT and/or NCAM, these data provide additional evidence for the
molecular complexity of mammalian taste bud cells. Supported by
NIDCD DC00347 to DVS.
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187 Poster [ ] Functional Organization of the Gustatory
System
PROLIFERATION OF LINGUAL MACROPHAGES AFTER
UNILATERAL DENERVATION OF FUNGIFORM TASTE
BUDS.
Mccluskey L.P. 1, Rigsby C.S. 1 1Physiology, Medical College of
Georgia, Augusta, GA
Within days after unilateral chorda tympani nerve (CT) section,
activated ED1+ macrophages are increased on both the sectioned and
intact sides of the tongue. Activated macrophages release a variety of
cytokines and growth factors, which are proposed to affect sodium taste
function after neural injury. We hypothesized that local proliferation of
ED1+ macrophages accounts for the dramatic increase observed after
nerve section. SD specified pathogen-free rats received unilateral CT
section or sham section on day 0. On day 1 or 2 post-section, rats were
given an injection of BrdU (50 mg / kg i.p.) 6 hr prior to sacrifice.
Paraffin sections were processed for double immunofluorescent staining
with antibodies to BrdU and ED1. As previously observed, there was an
increase in ED1+ macrophages at both day 1 and day 2 post-sectioning.
However, while BrdU+ cells were also numerous throughout tongue,
few cells were double-positive. Therefore, ED1+ macrophages do not
appear to proliferate in the lingual environment in response to
denervation. We next examined whether the increase in ED1+
macrophages might be due to proliferation of resting, resident ED2+
macrophages that convert to an activated phenotype. Yet there were
also few ED2+ / BrdU+ cells after nerve section, suggesting that
proliferation of ED2+ macrophages does not account for the increased
ED1+ population at these time points. We are currently examining the
possibility that circulating ED1+ cells enter the tongue in response to
denervation. Resolving this issue will increase our understanding of
potential immune mechanisms that regulate peripheral taste function.
Supported by NIH grant 1 R01 DC005811-01A1.
188 Slide [ ] Beidler Colloquium on Taste Transduction
THE MAMMALIAN AMILORIDE-INSENSITIVE (AI) NON-
SPECIFIC SALT TASTE RECEPTOR IS A VANILLOID
RECEPTOR-1 (VR-1) VARIANT
Lyall V. 1, Heck G.L. 1, Vinnikova A.K. 2, Ghosh S. 2, Phan T.T. 1, Bigbee
J.W. 3, Desimone J.A. 1 1Physiology, Virginia Commonwealth
University, Richmond, VA; 2Internal Medicine, Virginia Commonwealth
University, Richmond, VA; 3Anatomy and Neurobiology, Virginia
Commonwealth University, Richmond, VA
The AI non-specific salt taste receptor is the predominant transducer
of salt taste in some mammalian species, including humans. The
physiological, pharmacological and biochemical properties of the AI
salt taste receptor were investigated by RT-PCR, direct measurement of
unilateral apical Na + fluxes in polarized rat fungiform taste receptor
cells (TRCs), and chorda tympani (CT) nerve recordings to lingual
stimulation with NaCl, KCl, NH Cl and CaCl , in both the rat model
4 2
and the VR-1 knockout mouse model. We report that the AI salt taste
receptor is a constitutively active non-selective cation channel derived
from the VR-1 gene. It accounts for all of the AI CT response to Na +
salts and part of the response to K + , NH4 + , and Ca2+ salts. It is activated
by vanilloids (resiniferatoxin and capsaicin) and temperature (>38oC), and is inhibited by VR-1 antagonists (capsazepine and SB-366791). In
the presence of vanilloids, external H + and ATP lower the temperature
threshold of the channel. This allows for increased salt taste sensitivity
without an increase in temperature. VR-1 knockout mice demonstrate
no functional AI salt taste receptor and no salt taste sensitivity to
vanilloids and temperature. We conclude that the mammalian AI nonspecific
salt taste receptor is a VR-1 variant. Supported by NIDCD
Grants DC-02422 and DC-00122.