6,623 research outputs found
Na(V)1.5 sodium channel window currents contribute to spontaneous firing in olfactory sensory neurons
Olfactory sensory neurons (OSNs) fire spontaneously as well as in response to odor; both forms of firing are physiologically important. We studied voltage-gated Na+ channels in OSNs to assess their role in spontaneous activity. Whole cell patch-clamp recordings from OSNs demonstrated both tetrodotoxin-sensitive and tetrodotoxin-resistant components of Na+ current. RT-PCR showed mRNAs for five of the nine different Na+ channel α-subunits in olfactory tissue; only one was tetrodotoxin resistant, the so-called cardiac subtype NaV1.5. Immunohistochemical analysis indicated that NaV1.5 is present in the apical knob of OSN dendrites but not in the axon. The NaV1.5 channels in OSNs exhibited two important features: 1) a half-inactivation potential near −100 mV, well below the resting potential, and 2) a window current centered near the resting potential. The negative half-inactivation potential renders most NaV1.5 channels in OSNs inactivated at the resting potential, while the window current indicates that the minor fraction of noninactivated NaV1.5 channels have a small probability of opening spontaneously at the resting potential. When the tetrodotoxin-sensitive Na+ channels were blocked by nanomolar tetrodotoxin at the resting potential, spontaneous firing was suppressed as expected. Furthermore, selectively blocking NaV1.5 channels with Zn2+ in the absence of tetrodotoxin also suppressed spontaneous firing, indicating that NaV1.5 channels are required for spontaneous activity despite resting inactivation. We propose that window currents produced by noninactivated NaV1.5 channels are one source of the generator potentials that trigger spontaneous firing, while the upstroke and propagation of action potentials in OSNs are borne by the tetrodotoxin-sensitive Na+ channel subtypes.This work was aided by support from Boston University, the Rocky Mountain Taste and Smell Center Core for Cellular Visualization and Analysis [National Institute on Deafness and Other Communication Disorders (NIDCD) P30 DC-04657; D. Restrepo, principal investigator], and NIDCD Grants DC-04863 to V. Dionne and DC-006070 to D. Restrepo and T. E. Finger. (Boston University; P30 DC-04657 - Rocky Mountain Taste and Smell Center Core for Cellular Visualization and Analysis [National Institute on Deafness and Other Communication Disorders (NIDCD)]; DC-04863 - Rocky Mountain Taste and Smell Center Core for Cellular Visualization and Analysis [National Institute on Deafness and Other Communication Disorders (NIDCD)]; DC-006070 - Rocky Mountain Taste and Smell Center Core for Cellular Visualization and Analysis [National Institute on Deafness and Other Communication Disorders (NIDCD)])https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4122723/Accepted manuscrip
Simulation and observations of stratospheric aerosols from the 2009 Sarychev volcanic eruption
We used a general circulation model of Earth’s climate to conduct simulations of the 12-16 June 2009 eruption of Sarychev volcano (48.1°N, 153.2°E). The model simulates the formation and transport of the stratospheric sulfate aerosol cloud from the eruption and the resulting climate response. We compared optical depth results from these simulations with limb scatter measurements from the Optical Spectrograph and InfraRed Imaging System (OSIRIS), in situ measurements from balloon-borne instruments lofted from Laramie, Wyoming (41.3°N, 105.7°W), and five lidar stations located throughout the Northern Hemisphere. The aerosol cloud covered most of the Northern Hemisphere, extending slightly into the tropics, with peak backscatter measured between 12 and 16 km in altitude. Aerosol concentrations returned to near background levels by Spring, 2010. After accounting for expected sources of discrepancy between each of the data sources, the magnitudes and spatial distributions of aerosol optical depth due to the eruption largely agree. In conducting the simulations, we likely overestimated both particle size and the amount of SO2 injected into the stratosphere, resulting in modeled optical depth values that were a factor of 2-4 too high. Model results of optical depth due to the eruption show a peak too late in high latitudes and too early in low latitudes, suggesting a problem with stratospheric circulation in the model. The model also shows a higher annual decay rate in optical depth than is observed, showing an inaccuracy in seasonal deposition rates. The modeled deposition rate of sulfate aerosols from the Sarychev eruption is higher than the rate calculated for aerosols from the 1991 eruption of Mt. Pinatubo
Expression of Galpha14 in sweet-transducing taste cells of the posterior tongue
<p>Abstract</p> <p>Background</p> <p>"Type II"/Receptor cells express G protein-coupled receptors (GPCRs) for sweet, umami (T1Rs and mGluRs) or bitter (T2Rs), as well as the proteins for downstream signalling cascades. Transduction downstream of T1Rs and T2Rs relies on G-protein and PLCβ2-mediated release of stored Ca<sup>2+</sup>. Whereas Gαgus (gustducin) couples to the T2R (bitter) receptors, which Gα-subunit couples to the sweet (T1R2 + T1R3) receptor is presently not known. We utilized RT-PCR, immunocytochemistry and single-cell gene expression profiling to examine the expression of the Gαq family (q, 11, 14) in mouse taste buds.</p> <p>Results</p> <p>By RT-PCR, Gα14 is expressed strongly and in a taste selective manner in posterior (vallate and foliate), but not anterior (fungiform and palate) taste fields. Gαq and Gα11, although detectable, are not expressed in a taste-selective fashion. Further, expression of Gα14 mRNA is limited to Type II/Receptor cells in taste buds. Immunocytochemistry on vallate papillae using a broad Gαq family antiserum reveals specific staining only in Type II taste cells (i.e. those expressing TrpM5 and PLCβ2). This staining persists in Gαq knockout mice and immunostaining with a Gα11-specific antiserum shows no immunoreactivity in taste buds. Taken together, these data show that Gα14 is the dominant Gαq family member detected. Immunoreactivity for Gα14 strongly correlates with expression of T1R3, the taste receptor subunit present in taste cells responsive to either umami or sweet. Single cell gene expression profiling confirms a tight correlation between the expression of Gα14 and both T1R2 and T1R3, the receptor combination that forms sweet taste receptors.</p> <p>Conclusion</p> <p>Gα14 is co-expressed with the sweet taste receptor in posterior tongue, although not in anterior tongue. Thus, sweet taste transduction may rely on different downstream transduction elements in posterior and anterior taste fields.</p
Dust-Gas Scaling Relations and OH Abundance in the Galactic ISM
Observations of interstellar dust are often used as a proxy for total gas
column density . By comparing thermal dust data
(Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS (Green et
al. 2018), with accurate (opacity-corrected) HI column densities and
newly-published OH data from the Arecibo Millennium survey and 21-SPONGE, we
confirm linear correlations between dust optical depth , reddening
and the total proton column density in the range
(130)10cm, along sightlines with no molecular gas
detections in emission. We derive an / ratio of
(9.41.6)10cmmag for purely atomic sightlines
at 5, which is 60 higher than the canonical value of
Bohlin et al. (1978). We report a 40 increase in opacity
=/, when moving from the low column
density (510cm) to moderate column
density (510cm) regime, and suggest that
this rise is due to the evolution of dust grains in the atomic ISM. Failure to
account for HI opacity can cause an additional apparent rise in ,
of the order of a further 20. We estimate molecular hydrogen column
densities from our derived linear relations, and hence
derive the OH/H abundance ratio of 110
for all molecular sightlines. Our results show no evidence of systematic trends
in OH abundance with in the range
(0.110)10cm. This suggests
that OH may be used as a reliable proxy for H in this range, which includes
sightlines with both CO-dark and CO-bright gas.Comment: The revised manuscript is accepted for publication in The
Astrophysical Journa
Immunohistochemical localization of enkephalin and ACTH-related substances in the pituitary of the lamprey
The distributions of ACTH-, αMSH-, β LPH-, and enkephalin-related substances were determined immunohistochemically in the pituitary of the brook lamprey, Lampetra lamotenii . An antiserum directed against the middle region of ACTH reacted chiefly with cells in the proadenohypophysis. An antiserum specific for αMSH reacted with all of the cells of the meta-adenohypophysis, but did not react with any of the middle ACTH-positive cells in the pro-adenohypophysis. Several antisera which crossreact with both β LPH and β -endorphin did not react with any region of the lamprey pituitary. However, an antiserum directed against γLPH did react with a small population of cells in the meso-adenohypophysis. This reactivity could be blocked following pre-absorption with mouse β LPH but was not blocked by synthetic β -endorphin(1–31).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/47679/1/441_2004_Article_BF00213730.pd
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Is TrpM5 a reliable marker for chemosensory cells? Multiple types of microvillous cells in the main olfactory epithelium of mice
<p>Abstract</p> <p>Background</p> <p>In the past, ciliated receptor neurons, basal cells, and supporting cells were considered the principal components of the main olfactory epithelium. Several studies reported the presence of microvillous cells but their function is unknown. A recent report showed cells in the main olfactory epithelium that express the transient receptor potential channel TrpM5 claiming that these cells are chemosensory and that TrpM5 is an intrinsic signaling component of mammalian chemosensory organs. We asked whether the TrpM5-positive cells in the olfactory epithelium are microvillous and whether they belong to a chemosensory system, i.e. are olfactory neurons or trigeminally-innervated solitary chemosensory cells.</p> <p>Results</p> <p>We investigated the main olfactory epithelium of mice at the light and electron microscopic level and describe several subpopulations of microvillous cells. The ultrastructure of the microvillous cells reveals at least three morphologically different types two of which express the TrpM5 channel. None of these cells have an axon that projects to the olfactory bulb. Tests with a large panel of cell markers indicate that the TrpM5-positive cells are not sensory since they express neither neuronal markers nor are contacted by trigeminal nerve fibers.</p> <p>Conclusion</p> <p>We conclude that TrpM5 is not a reliable marker for chemosensory cells. The TrpM5-positive cells of the olfactory epithelium are microvillous and may be chemoresponsive albeit not part of the sensory apparatus. Activity of these microvillous cells may however influence functionality of local elements of the olfactory system.</p
Dust–Gas Scaling Relations and OH Abundance in the Galactic ISM
Observations of interstellar dust are often used as a proxy for total gas column density NH. By comparing Planck thermal dust data (Release 1.2) and new dust reddening maps from Pan-STARRS 1 and 2MASS, with accurate (opacity-corrected) H I column densities and newly published OH data from the Arecibo Millennium survey and 21-SPONGE, we confirm linear correlations between dust optical depth τ353, reddening E(B − V), and the total proton column density NH in the range (1–30) × 1020 cm−2, along sightlines with no molecular gas detections in emission. We derive an NH/E(B − V) ratio of (9.4 ± 1.6) × 1021 cm−2 mag−1 for purely atomic sightlines at |b| \u3e 5°, which is 60% higher than the canonical value of Bohlin et al. We report a ~40% increase in opacity σ353 = τ 353/NH, when moving from the low column density (NH \u3c 5 × 1020 cm−2) to the moderate column density (NH \u3e 5 × 1020 cm−2) regime, and suggest that this rise is due to the evolution of dust grains in the atomic interstellar medium. Failure to account for H I opacity can cause an additional apparent rise in σ353 of the order of a further ~20%. We estimate molecular hydrogen column densities NH2 from our derived linear relations, and hence derive the OH/H2 abundance ratio of XOH ~ 1 × 10−7 for all molecular sightlines. Our results show no evidence of systematic trends in OH abundance with NH2 in the range NH2 ~ (0.1−10) × 1021 cm−2. This suggests that OH may be used as a reliable proxy for H2 in this range, which includes sightlines with both CO-dark and CO-bright gas
Critique of a Pion Exchange Model for Interquark Forces
I describe four serious defects of a widely discussed pion exchange model for
interquark forces: it doesn't solve the "spin-orbit problem" as advertised, it
fails to describe the internal structure of baryon resonances, it leads to
disastrous conclusions when extended to mesons, and it is not reasonably
connected to the physics of heavy-light systems.Comment: 20 pages, 6 figures; some clarifications and references adde
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