1,721,053 research outputs found
Hair cells
No full textHair cells are the sensory receptors in the inner ear that
detect sound and head motion to begin the processes of
hearing and balance control. The defining feature of hair
cells is the hair bundle, the transduction organelle protruding
from their apical surface composed of ordered
arrays of stereocilia. Mechanical deflection of the hair
bundle, normally induced by physiological stimuli,
increases the open probability of mechanically gated
cation channels located at the tip of stereocilia. The
resulting depolarizing inward current generates a receptor
potential. The information encoded in this electrical
response is transmitted to the auditory or vestibular
afferent nerve fibres via the Ca2+-induced release of
neurotransmitter from the hair cell’s basal pole. In this
way sensory information is relayed to the brain enabling
us to perceive sound and maintain balance. In mammals,
hair cell loss causes irreversible balance and hearing
impairment because these sensory cells show very little or
no regenerative ability
Hair Cells
No full textThe auditory and the vestibular systems use hair
cells (HCs) as their sensory receptors. HCs are neu roepithelial cells characterised by the presence of
a bundle of microvilli-like structures that protrude
from their apical surface, called stereocilia. The
displacement of stereocilia, which is caused by
acoustic stimuli in the cochlea or head movement
in the vestibule, is converted into a depolarising
inward current by mechanoelectrical transducer
(MET) channels located at their tip. The depolarisa tion of HCs opens voltage-dependent Ca2+ channels
at their basolateral synaptic active zones, which
are functionally coupled to glutamate-containing
vesicles at specialised ribbon synapses. There is
also evidence for a nonquantal synaptic transmis sion at the vestibular HCs, likely involving direct
postsynaptic depolarisation by K+ exiting the cells.
In mammals, HC loss causes irreversible balance
and hearing impairment because these cells do not
regenerate
Non-NMDA receptors mediate glutamate-induced depolarization in frog crista ampullaris
No full textThe effect of glutamate on frog crista ampullaris was investigated in order to assess the potential role of this agent as an afferent transmitter in inner ear organs. Intracellular recordings from single afferent axons in the isolated labyrinth showed that, after blocking synaptic transmission with high concentrations of Mg2+, micro-injections of glutamate elicit a dose-dependent postsynaptic depolarization. The amplitude of depolarization was reduced dose-dependently by the competitive non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione. When Na+ concentration in the bath was progressively reduced, depolarization decreased gradually and disappeared almost completely in Na(+)-free Ringer. On the contrary, complete substitution of Ca2+ ions in the bath was without apparent effects. These results indicate that the postsynaptic depolarization induced by glutamate in frog semicircular canals involves the activation of non-NMDA amino acid receptors
L-type Ca channel biophysical properties in vestibular hair cells
No full textIt is presented a description of the elementary properties of voltage-dependent L-type Ca channels expressed by chicken embryo vestibularc hair cell
Excitability properties of rat vestibulocerebellum interneurons
No full textThe excitability properties of rat vestibulocerebellum interneurons were investigated by using the patch-clamp technique in combination with the slice preparation of the vestibulocerebellum. Intrinsic and extrinsic (response to mossy fiber activation) properties are described
Single L-type calcium currents in chick embryo vestibular type I and type II hair cells.
No full textThe study describes the properties of voltage-dependent Ca channels expressed by chick embryo vestibular hair cells. Experiments were performed by using the cell-attached configuration of the patch-clamp technique in combination with the fresh slice preparation of the crista ampullaris. Results show that chicken embryo type I and type II semicircular canal hair cells express a similar calcium channel population. Biophysical and pharmacological properties indicate that inward Ca2+ currents in both hair cell types are carried through L-type Ca channels
Single channel pKir inwardly rectifying currents from pigeon vestibular hair cells
No full textThe study describes the elementary properties of the Inward (anomalous) K rectifier channel expressed by pigeon vestibular hair cells. Experiments were performed by using the cell-attached configuration of the patch-clamp technique in combination with the slice preparation of the pigeon crista ampullaris
Isolation of A-type K+ current in hair cells of the frog crista ampullaris
No full textDifferent procedures to isolate the K+ A-type current (IA) from other membrane currents were tested on the complex inactivating outward K+ current generated in hair cells from the peripheral regions of the frog crista ampullaris. Experiments were performed in thin slices of epithelium using the whole-cell configuration of the patch-clamp technique. The conventional conditioning voltage protocol did not allow a satisfactory isolation of IA, due to the presence of other K+ currents showing overlapping steady-state inactivation properties. An attempt to block other K+ currents using calcium-free saline containing 50 mM TEA also failed to provide a satisfactory isolation of IA, due to contamination by a residual sustained current, probably consisting of a slow delayed outward K+ current (IK). Use of the selective A-channel blocker 4-aminopyridine (4-AP) at concentrations < 12 mM was also unsatisfactory because at these concentrations 4-AP produced a voltage-dependent blockade. Conversely, use of 4-AP at concentrations of 15-20 mM allowed a good separation of an uncontaminated IA. These results indicate that IA in hair cells of vestibular epithelium can be isolated most effectively by the 4-AP procedure, provided that sufficiently high concentrations of the A-channel blocker are used
Electrophysiological properties of vestibular sensory and supporting cells in the labirynth slice: Before and during regeneration.
No full textThe whole cell patch-clamp technique in combination with the slice preparation was used to investigate the electrophysiological properties of pigeon semicircular canal sensory and supporting cells. These properties were also characterized in regenerating neuroepithelia of pigeons preinjected with streptomycin to kill the hair cells. Type II hair cells from each of the three semicircular canals showed similar, topographically related patterns of passive and active membrane properties. Hair cells located in the peripheral regions (zone I, near the planum semilunatum) had less negative resting potentials [0-current voltage in current-clamp mode (Vz) = -62.8 +/- 8.7 mV, mean +/- SD; n = 13] and smaller membrane capacitances (Cm = 5.0 +/- 0.9 pF, n = 14) than cells of the intermediate (zone II; Vz = -79.3 +/- 7.5 mV, n = 3; Cm = 5.9 +/- 1.2 pF, n = 4) and central (zone III; Vz = -68.0 +/- 9.6 mV, n = 17; Cm = 7.1 +/- 1.5 pF, n = 18) regions. In peripheral hair cells, ionic currents were dominated by a rapidly activating/inactivating outward K+ current, presumably an A-type K+ current (IKA). Little or no inwardly rectifying current was present in these cells. Conversely, ionic currents of central hair cells were dominated by a slowly activating/inactivating outward K+ current resembling a delayed rectifier K+ current (IKD). Moreover, an inward rectifying current at voltages negative to -80 mV was present in all central cells. This current was composed of two components: a slowly activating, noninactivating component (Ih), described in photoreceptors and saccular hair cells, and a faster-activating, partially inactivating component (IK1) also described in saccular hair cells in some species. Ih and IK1 were sometimes independently expressed by hair cells. Hair cells located in the intermediate region (zone II) had ionic currents more similar to those of central hair cells than peripheral hair cells. Outward currents in intermediate hair cells activated only slightly more quickly than those of the cells of the central region, but much more slowly than those of the peripheral cells. Additionally, intermediate hair cells, like central hair cells, always expressed an inward rectifying current. The regional distribution of outward rectifying potassium conductances resulted in macroscopic currents differing in peak-to-steady state ratio. We quantified this by measuring the peak (Gp) and steady-state (Gs) slope conductance in the linear region of the current-voltage relationship (-40 to 0 mV) for the hair cells located in the different zones. Gp/Gs average values (4.1 +/- 2.1, n = 15) from currents in peripheral hair cells were higher than those from intermediate hair cells (2.3 +/- 0.8, n = 4) and central hair cells(1.9 +/- 0.8, n = 21). The statistically significant differences (P < 0.001) in Gp/Gs ratios could be accounted for by KA channels being preferentially expressed in peripheral hair cells. Hair cell electrophysiological properties in animals pretreated with streptomycin were investigated at approximately 3 wk and approximately 9-10 wk post injection sequence (PIS). At 3 wk PIS, hair cells (all zones combined) had a statistically significantly (P < 0.001) lower Cm (4.6 +/- 1.1 pF, n = 24) and a statistically significantly (P < 0.01) lower Gp(48.4 +/- 20.8 nS, n = 26) than control animals (Cm = 6.2 +/- 1.6 pF, n = 36; Gp = 66 +/- 38.9 nS, n = 40). Regional differences in values of Vz, as well as the distribution of outward and inward rectifying currents, seen in control animals, were still obvious. But, differences in the relative contribution of the expression of the different ionic current components changed. This result could be explained by a relative decrease in IKA compared with IKD during that interval of regeneration, which was particularly evident in peripheral hair cells
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