1,720,968 research outputs found
Reverse transduction measured in the isolated cochlea by laser Michelson interferometry.
No full textIT is thought that the sensitivity of mammalian hearing depends on amplification of the incoming sound within the cochlea by a select population of sensory cells, the outer hair cells. It has been suggested that these cells sense displacements and feedback forces which enhance the basilar membrane motion by reducing the inherent damping of the cochlear partition1-7. In support of this hypothesis, outer hair cells show membrane-potential-induced length changes1-3 at acoustic rates. This process has been termed 'reverse transduction'. For amplification, the forces should be large enough to move the basilar membrane. Using a displacement-sensitive interferometer8, we tested this hypothesis in an isolated cochlea while stimulating the outer hair cells with current passed across the partition. We show here that the cochlear partition distorts under the action of electrically driven hair cell length changes and produces place-specific vibration of the basilar membrane of a magnitude comparable to that observed near auditory threshold (about 1 nm). Such measurements supply direct evidence that cochlear amplification arises from the properties of the outer hair cell population
Can you still see the cochlea for the molecules?
No full textIt is now established that the mammalian cochlea uses active amplification of incoming sound to achieve sensitivity. Cellular details are emerging slowly, Recent studies of sensory hair cells have highlighted the possible molecular bases for amplification and the components of sensitivity regulation within the cochlea: a synthesis is likely to depend on effective and physiologically informed modelling
Differential expression of outer hair cell potassium currents in the isolated cochlea of the guinea pig.
Full text link1. Whole-cell currents were recorded from outer hair cells (OHCs) in undissociated tissues from the organ of Corti. The experiments allowed ionic currents to be measured in cells with precise localization on the three most apical cochlear turns.
2. Two major potassium currents were expressed in the cells. One current, named I,, was half-activated at -24 mV and was most prominent in the most apical turn, turn 4. A second, named I-K,(n) was half-activated at -92 mV and was the major contributor to the current-voltage (I-V) curve of cells from the more basal turns, turns 3 and 2, of the cochlea.
3. I-K was specifically blocked by 100 mu M 4-aminopyridine (4-AP). In contrast, I-K,(n) was reduced by 5 mM external barium. Superfusion with zero calcium produced no effect on currents in the range from -60 to 0 mV, but reduced currents by a maximum of 15% outside this range.
4. The cell input conductance increased systematically from 3.4 nS in turn 4 to 40 nS in turn 2 measured at a holding potential of -70 mV.
5. The mean leak conductance, measured from the slope of the I-V curve at -110 mV,decreased systematically from 5.2 nS in turn 2, to 2.9 nS in turn 3 and 2.2 nS in turn 4.
6. These data show that hair cell properties can be determined in undissociated cells and are likely to pros ide a good estimate of the properties of the cells in the intact cochlea. Differences with the properties of isolated OHCs are discussed
A laser interferometer for sub nanometre measurements in the cochlea.
No full textA modification of a light microscope is described here which allows measurement of nanometre movements along the optical axis of the microscope. The light path is reflected off 10-mu m-diametre small glass beads which are individually imaged with the microscope objective. The interferometer is under computer control to allow it to remain in quadrature and so maximise sensitivity. The algorithm is described. Although the techniques are applied to detection of movements of the cochlear partition, they can be used to measure sub-micron movements of any reflecting structures accessible to microscopy
Purinergic control of intercellular communication between Hensen's cells of the guinea pig cochlea
Full text linkHensen's cells in the isolated cochlea were stimulated by extracellular adenosine 5 ' -triphosphate (XTP) applied to their endolymphatic surface while changes in membrane current and intracellular calcium concentration ([Ca(2+)](i)) were measured simultaneously. The response consisted of (i) an initial rapid inward current accompanied by elevation of the [Ca(2+)](i), (ii) a more slowly rising inward current accompanied by a rise of the [Ca(2+)](i) and (iii) a slowly developing reduction of input conductance
Patch clamped responses from outer hair cells in the intact adult organ of Corti.
No full textOuter hair cells (OHCs) from the mammalian cochlea act as both sensory cells and motor cells. We report here whole-cell tight seal recordings of OHC activity in their natural embedding tissue, the intact organ of Corti, using a temporal bone preparation. The mean cell resting potential, - 76 +/- 4 mV (n = 19) and input conductance (10 +/- 3 nS at - 70 mV) of third turn hair cells were significantly lower than have been found in isolated cells. Two main K+ currents in the cell were identified. One current, activated positive to - 100 mV, was reduced by 5mM BaCl2. The other current, activated above - 49 mV, was reduced by 100 mu M 4-aminopyridine (4-AP) and by 30 mM tetraethylammonium (TEA). Both of these currents have been also identified in recordings reported from isolated cells. On stepping to different membrane potentials, cells imaged in the organ of Corti changed length by an amount large enough to cause visible distortions in neighbouring cells. By quantifying such distortions we estimate that the forces generated by OHCs can account for the enhanced response to sound required by the cochlear amplifier
Dissecting the outer hair cell feedback loop.
No full textWe have investigated the mechanical responses of outer hair cells and their modulation by ATP
The pharmacology of the outer hair cell motor.
No full textSeveral observations have recently contributed significantly to our knowledge of the processes involved in the transmission of signals in the auditory system. These events include the mechanical motion pattern of the cochlear partition, the motion of hair cell cilia, gating of receptor currents, hair cell motility, synaptic transmission and signal processing in central nuclei and in the auditory cortex. Hearing may therefore be considered to arise from a series of active processes which modify the signals sent to the brain. This book provides the edited proceedings of a Wenner-Gren International Symposium held in Stockholm in May, 1994. Focusing on the dynamic aspects of the hearing process, the content represents the work of the major research laboratories in all fields of auditory research. The chapters are organized to proceed out from the brain, level by level, towards the periphery
Fast vesicle replenishment allows indefatigable signalling at the first auditory synapse
No full textRibbon-type synapses in inner hair cells of the mammalian cochlea encode the complexity of auditory signals by fast and tonic release through fusion of neurotransmitter-containing vesicles. At any instant, only about 100 vesicles are tethered to the synaptic ribbon, and about 14 of these are docked to the plasma membrane(1,2), constituting the readily releasable pool(3). Although this pool contains about the same number of vesicles as that of conventional synapses(4,5), ribbon release sites operate at rates of about two orders of magnitude higher(3,6,7) and with submillisecond precision(8-11). How these sites replenish their vesicles so efficiently remains unclear(3,12,13). We show here, using two-photon imaging of single release sites in the intact cochlea, that preformed vesicles derived from cytoplasmic vesicle-generating compartments(14) participate in fast release and replenishment. Vesicles were released at a maximal initial rate of 3 per millisecond during a depolarizing pulse, and were replenished at a rate of 1.9 per millisecond. We propose that such rapid resupply of vesicles enables temporally precise and sustained release rates. This may explain how the first auditory synapse can encode with indefatigable precision without having to rely on the slow, local endocytic vesicle cycle(7)
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