Article Figures & Data
Figures
- FIG. 1.
Transient receptor potential channel M5 (TRPM5)-expressing solitary chemosensory cells in the respiratory epithelium of the mouse nasal cavity. A: anterior nasal cavity viewed from a hemisected head from a TRPM5-green fluorescent protein (GFP) mouse, showing the GFP-positive solitary chemosensory cells densely populate the anterior part of the respiratory epithelium. A white circle indicats area where the event-related potential was recorded for Fig. 5. The anterior region of the main olfactory epithelium (MOE) is outlined in a white line. B: a magnified confocal image showing that the GFP-expressing cells are solitary, somewhat spindle-shaped. On average, there are 5,600 GFP-positive solitary chemosensory cells in the respiratory epithelium of a half nose. C: an image from a section through the respiratory epithelium showing that the apical processes (arrowhead) of a GFP-positive cell extends to the epithelial surface. D: a high-magnification confocal image from a whole mount of stripped epithelium showing several slender GFP-positive cells. Apical processes (arrowhead) and basal processes (arrow) emanate from the soma of these cells. E: anti-TRPM5 antibody (red) strongly labeled GFP-positive cells. The image was taken from a whole mount preparation of a stripped epithelium. Apical regions are marked by arrowheads. Scale bars: A, 1 mm; B, 50 μm, C–E, 10 μm.
- FIG. 2.
Co-localization of TRPM5 with α-gustducin and components of the phospholipase C (PLC) signaling pathway. Confocal images were taken from immunoreacted whole mount stripped epithelial tissue obtained from the TRPM5-GFP transgenic mice. TRPM5-expressing cells are GFP positive, shown in green. A: some but not all of the TRPM5-expressing cells immunoreacted with antibody against α-gustducin (marked by asterisks), showing that the population of TRPM5-expressing cells and α-gustducin–expressing cells overlapped but were not identical. Inset: an image from the anterior area showing more solitary chemosensory cells co-expressing GFP and α-gustducin. B and C: TRPM5-expressing cells also immunoreacted with PLCβ2 (B) and γ13 (C), respectively, suggesting that these cells express signaling elements of the PLC pathway similar to those in taste cells. Scale bars: 20 μm.
- FIG. 3.
Innervation of the TRPM5-expressing cells. Trigeminal nerve fibers in the nasal cavity were visualized using antibodies against PGP9.5 and substance P. A: a confocal image showed PGP-immunoreactive nerve fibers closely apposing GFP-expressing cells in a whole mount preparation (arrows). B: in sections through the epithelium, PGP9.5-positive fibers can be observed wrapping the basal region of a GFP-expressing SCC and coursing along the cell body (arrowheads). C: substance P–positive fiber contacting a TRPM5-expressing cell. Multiple button-like swellings (arrowheads) were seen. Inset: an optical section showing that, in several regions, the GFP-labeled cell surrounds the nerve fibers indented into the soma (arrowheads). Scales: A, 10 μm; B, C, and inset, 5 μm.
- FIG. 4.
Expression of a vesicle-associated membrane protein synaptobrevin-2 in TRPM5-positive cells. A: immunoreactivity for synaptobrevin-2 was seen in the TRPM5-expressing cells (arrows), as well as presumed peptidergic nerve fibers that run along the basal lamina of epithelium and in close apposition to the TRPM5 cells. B: synaptobrevin-2 immunoreactivity (red) overlaid with images of TRPM5 cells (green). C: a magnified image showing synaptobrevin-2–reactive processes and TRPM5 cells. Apical processes are indicated by arrowheads. Scale: 10 μm.
- FIG. 5.
Odorous stimuli-induced changes in the event-related potential (ERP). A: traces are the largest amplitude ERPs recorded in the anterior respiratory epithelia where dense TRPM5-expressing solitary chemosensory cells reside. A variety of chemicals at 0.5- to 5-mM concentrations induced responses, except nicotine, which induced sizable responses at 50 μM. Ringer solution did not induced visible changes in ERP (control). The ERP responses were repeatable. B: the ERP amplitudes for individual stimuli (5 mM) were averaged from 3–7 traces. C: the ERP responses are concentration dependent. At 0.1 mM, citral, lilial, and valeric acid did not induce visible ERPs. At concentrations of 1 or 5 mM, these same stimuli elicited measurable ERPs.
- FIG. 6.
Odors at high concentrations induce changes in intracellular Ca2+ levels in isolated GFP (TRPM5)-expressing cells. A: typical responses to various odors at 500 μM from the GFP-expressing cells. Response to lilial was repeated in the same cells. The evoked responses were repeatable. Bars indicate the stimulation periods. GFP (TRPM5)-expressing cells also respond to CO2 acommon trigeminal stimulus. 2,5-DMP, 2,5 dimethylpyrazine. B: concentration-dependent response curves for geraniol and lilial. Plotted values are percent changes from the resting Ca2+ levels. GFP (TRPM5)-expressing cells only responded to concentrations >100 μM. Data are obtained from 4 cells tested with 20-, 100-, and 500-μM stimuli. C: inhibition by the PLC inhibitor U73122. C1: lilial (500 μM)-evoked Ca2+ responses (left). The response was suppressed in the presence of U73122 (5 μM). These 2 recordings were from the same cell. The effect of U73122 was partially recoverable. C2: summary of U73122-induced inhibition. Peaks of responses to lilial at 500 μM were measured from both control and U73122-treated conditions in the same cells. For each cell, the peak value of responses in the presence of U73122 was normalized to the value of the control response. U73122 inhibited the lilial-evoked Ca2+ changes in the solitary chemosensory cells significantly (paired t-test, P = 0.019, n = 5).
- FIG. 7.
Responding profile of GFP-expressing solitary chemosensory cells. GFP-expressing cells respond to volatile stimuli. A total of 18 responding cells were stimulated with 4 or more chemicals. •, cell responded; ○, cell did not respond.
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