120,197 research outputs found
Actin instability alters red blood cell mechanics and Piezo1 channel activity
No full textThe organization and dynamics of the spectrin-actin membrane cytoskeleton play a crucial role in determining the mechanical properties of red blood cells (RBC). RBC are subjected to various forces that induce deformation during blood microcirculation. Such forces also regulate membrane tension, leading to Piezo1 channel activation, which is functionally linked to RBC dehydration through calcium influx and subsequent activation of Gardos channels, ultimately resulting in variations in RBC volume. In this study, we investigated how actin instability affects Piezo1 channel gating, in relation to RBC deformation and mechanical properties, using micropipette aspiration and optical tweezers. Actin instability, induced by 0.5 μM Cytochalasin-D (Cyt-D), led to a 22% reduction in the activation pressure. Additionally, we observed a decreasing trend in Young's modulus, membrane tension, and viscosity. By measuring the time required for cell shape recovery after deformation in an optical trap, we found that Cyt-D-treated RBC took approximately 14% longer to recover compared to untreated cells. The bimodal imaging feature of our experimental approach allowed us to simultaneously measure and correlate activation pressure with mechanical properties at the single-cell level. A significant correlation was found between these parameters in both treated and untreated RBC. Our findings demonstrate the influence of actin instability on both Piezo1 activation and RBC mechanics. These results offer new insights into the interplay between F-actin and Piezo1 in RBC mechanobiology
Dirac cohomology of one-W-type representations
No full textThe smooth hermitian representations of a split reductive p-adic group whose restriction to a maximal hyperspecial compact subgroup contain a single K-type with Iwahori fixed vectors have been studied in [D. Barbasch, A. Moy, Classification of one K-type representations, Trans. Amer. Math. Soc. 351 (1999), no. 10, 4245-4261] in the more general setting of modules for graded affine Hecke algebras with parameters. We show that every such one K-type module has nonzero Dirac cohomology (in the sense of [D. Barbasch, D. Ciubotaru, P. Trapa, The Dirac operator for graded affine Hecke algebras, arXiv:1006.3822]), and use Dirac operator techniques to determine the semisimple part of the Langlands parameter for these modules, thus completing their classification
Design and Construction of a Cost-Effective Spinning Disk System for Live Imaging of Inner Ear Tissue
No full textConfocal imaging of fluorescent probes offers a powerful, non-invasive tool which enables data collection from vast population of cells at high spatial and temporal resolution. Spinning disk confocal microscopy parallelizes the imaging process permitting the study of dynamic events in populations of living cells on the millisecond time scale. Several spinning disk microscopy solutions are commercially available, however these are often poorly configurable and relatively expensive. This chapter describes a procedure to assemble a cost-effective homemade spinning disk system for fluorescence microscopy, which is highly flexible and easily configurable. We finally illustrate a reliable protocol to obtain high-quality Ca(2+) and voltage imaging data from cochlear preparations
Sensing noise damage in the inner ear through intercellular calcium waves
No full textOur sense of hearing requires functional sensory hair cells. Throughout life those hair cells are subjected to various traumas, the most common being loud sound. The primary effect of acoustic trauma is manifested as damage to the delicate mechanosensory apparatus of the hair cell stereocilia [1]. This may eventually lead to hair cell death [2] and irreversible deafness [3]. Little is known about the way in which noxious sound stimuli affect individual cellular components of the auditory sensory epithelium. However, studies in different types of cell cultures have shown that damage and mechanical stimulation can activate changes in intracellular free calcium concentration ([Ca(2+)](i)) and elicit intercellular Ca(2+) waves [4]. Thus an attractive hypothesis is that changes in [Ca(2+)](i), propagating as a wave through support cells in the organ of Corti, may constitute a fundamental mechanism to signal the occurrence of hair cell damage. The mechanism we describe here exhibits nanomolar sensitivity to extracellular ATP, involves regenerative propagation of intercellular calcium waves due to ATP originating from hair cells, and depends on functional IP(3)-sensitive intracellular stores in support cells
Presynaptic Calcium Stores Modulate Afferent Release in Vestibular Hair Cells
No full textHair cells, the mechanoreceptors of the acoustic and vestibular system, are presynaptic to primary afferent neurons of the eighth nerve and excite neural activity by the release of glutamate. In the present work, the role played by intracellular Ca2+ stores in afferent transmission was investigated, at the presynaptic level, by monitoring changes in the intracellular Ca2+ concentration [Ca2+]i in vestibular hair cells, and, at the postsynaptic level, by recording from single vestibular afferent fibers. Application of 1-10 mM caffeine to hair cells potentiated Ca2+ responses evoked by depolarization at selected Ca2+ hotspots, and also induced a graded increase in celi membrane capacitance (deltaCm), signaling exocytosis of transmìtter. Ca2+ signals evoked by caffeine peaked in a region located about 10 microm from the base of the hair cell. Similarly localized [Ca2+]i increases were observed following 500 ms depolarizations, but not with 50 ms depolarizations, suggesting the occurrence of calcium-induced calcium release (CICR) from the same stores. Both [Ca]i and deltaCm responses were inhibited following incubation wìth ryanodine (40 microM) for 8-10 min. Consistent with these results, afferent transmission was potentiated by caffeine and inhibited by ryanodine both at the level of action potentials (APs) and of excitatory postsynaptic potentials (EPSP). Neither caffeine nor ryanodine affected the shape and amplitude of miniature EPSP (mEPSP), indicating that both drugs acted at the presynaptic level. These results strongly suggest that endogenous modulators of the CICR process will affect afferent activity elicited by mechanical stimuli in the physiological frequency range
Numerical analysis of a 3-D printed porous trailing edge for broadband noise reduction
No full textLattice Boltzmann simulations were carried out to investigate the noise mitigation mechanisms of a 3-D printed porous trailing-edge insert, elucidating the link between noise reduction and material permeability. The porous insert is based on a unit cell resembling a lattice of diamond atoms. It replaces the last 20 % chord of a NACA 0018 at zero angle-of-attack. A partially blocked insert is considered by adding a solid partition between 84 % and 96 % of the aerofoil chord. The regular porous insert achieves a substantial noise reduction at low frequencies, although a slight noise increase is found at high frequencies. The partially blocked porous insert exhibits a lower noise reduction level, but the noise emission at mid-to-high frequency is slightly affected. The segment of the porous insert near the tip plays a dominant role in promoting noise mitigation, whereas the solid-porous junction contributes, in addition to the rough surface, towards the high-frequency excess noise. The current study demonstrates the existence of an entrance length associated with the porous material geometry, which is linked to the pressure release process that is responsible for promoting noise mitigation. This process is characterised by the aerodynamic interaction between pressure fluctuations across the porous medium, which is found at locations where the porous insert thickness is less than twice the entrance length. Present results also suggest that the noise attenuation level is related to both the chordwise extent of the porous insert and the streamwise turbulent length scale. The porous inserts also cause a slight drag increase compared to their solid counterpart. Wind Energ
Purinergic signalling and intercellular Ca2+ wave propagation in the organ of Corti
No full textExtracellular ATP is a key neuromodulator of visual and auditory sensory epithelia. In the rat cochlea, pharmacological dissection indicates that ATP, acting through a highly sensitive purinergic/IP(3)-mediated signaling pathway with (little or) no involvement of ryanodine receptors, is the principal paracrine mediator implicated in the propagation of calcium waves through supporting and epithelial cells. Measurement of sensitivity to UTP and other purinergic agonists implicate P2Y(2) and P2Y(4) as the main P2Y receptor isoforms involved in these responses. Ca2+ waves, elicited under highly reproducible conditions by carefully controlling dose (1 microM) and timing of focal agonist application (0.2s), extended over radial distance greater than 160 microm from the source, identical to those activated by damaging single outer hair cells. Altogether, these results indicate that intercellular calcium waves are a robust phenomenon that confers a significant ability for cell-cell communication in the mammalian cochlea. Further ongoing research will reveal the roles that such Ca2+ waves play in the inner ear
Permeability and Gating Properties of Human Connexins 26 and 30 expressed in HeLa cells.
No full textHuman connexins 26 and 30 were expressed either through the bicistronic pIRES-EGFP expression vector or as EYFP-tagged chimeras. When transiently transfected in communication-incompetent HeLa cells, hCx26–pIRES transfectants were permeable to dyes up to 622 Da, but were significantly less permeable to 759 Da molecules. Under the same conditions, permeability of hCx26–EYFP fusion products was comparable to that of hCx26–pIRES, but with significant increase in diffusion at 759 Da, possibly as a consequence of having selected large fluorescent junctional plaques. Dye transfer was limited to 457 Da in hCx30–EYFP transfectants. When reconstructed from confocal serial sections, fluorescent plaques formed by hCx26–EYFP and hCx30–EYFP appeared irregular, often with long protrusions or deep invagination. Similar plaques were observed following immunostaining both in cells transfected with hCx26–pIRES and in HeLa cells stably transfected with mouse Cx26. Tissue conductance (Tgj) displayed significantly smaller values (28.8 ± 1.8 nS) for stably transfected mCx26 than transiently transfected hCx26 (43.5 ± 3.3 nS). These differences reflected in distinct functional dependence of normalized junctional conductance (Gj) on transjunctional voltage (Vj). The half-activation voltage for Gj was close to ±95 and ±58 mV in mCx26 and hCx26, respectively. The corresponding parameters for hCx30 transfectants were Tgj=45.2±3.5 nS and V0=±34 mV. These results highlight unexpected differences between mCx26 and hCx26 in this expression system, reinforce the concept that channel permeability may be related to Cx level expression, and indicate that fusion of hCx30 to GFP colour mutants produces channels that are suitable for permeability and gating studies
A 2 h periodic variation in the low-mass X-ray binary Ser X-1
No full textSpectroscopy of the low-mass X-ray binary Ser X-1 using the Gran Telescopio Canarias have revealed a ?2 h periodic variability that is present in the three strongest emission lines. We tentatively interpret this variability as due to orbital motion, making it the first indication of the orbital period of Ser X-1. Together with the fact that the emission lines are remarkably narrow, but still resolved, we show that a main-sequence K dwarf together with a canonical 1.4 M? neutron star gives a good description of the system. In this scenario, the most likely place for the emission lines to arise is the accretion disc, instead of a localized region in the binary (such as the irradiated surface or the stream-impact point), and their narrowness is due instead to the low inclination (?10°) of Ser X-1
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