scholarly journals The Physiology of Mechanoelectrical Transduction Channels in Hearing

2014 ◽  
Vol 94 (3) ◽  
pp. 951-986 ◽  
Author(s):  
Robert Fettiplace ◽  
Kyunghee X. Kim
Keyword(s):  
Hair Cell ◽  
Single Channel ◽  
Single Gene ◽  
Sensorineural Deafness ◽  
Coupled Processes ◽  
Resting Potential ◽  
Mechanical Stimuli ◽  
Open Probability ◽  
Tip Link

Much is known about the mechanotransducer (MT) channels mediating transduction in hair cells of the vertrbrate inner ear. With the use of isolated preparations, it is experimentally feasible to deliver precise mechanical stimuli to individual cells and record the ensuing transducer currents. This approach has shown that small (1–100 nm) deflections of the hair-cell stereociliary bundle are transmitted via interciliary tip links to open MT channels at the tops of the stereocilia. These channels are cation-permeable with a high selectivity for Ca2+; two channels are thought to be localized at the lower end of the tip link, each with a large single-channel conductance that increases from the low- to high-frequency end of the cochlea. Ca2+ influx through open channels regulates their resting open probability, which may contribute to setting the hair cell resting potential in vivo. Ca2+ also controls transducer fast adaptation and force generation by the hair bundle, the two coupled processes increasing in speed from cochlear apex to base. The molecular intricacy of the stereocilary bundle and the transduction apparatus is reflected by the large number of single-gene mutations that are linked to sensorineural deafness, especially those in Usher syndrome. Studies of such mutants have led to the discovery of many of the molecules of the transduction complex, including the tip link and its attachments to the stereociliary core. However, the MT channel protein is still not firmly identified, nor is it known whether the channel is activated by force delivered through accessory proteins or by deformation of the lipid bilayer.

scholarly journals Human TRPA1 is an inherently mechanosensitive bilayer-gated ion channel

2020 ◽  
Author(s):  
Lavanya Moparthi ◽  
Peter M. Zygmunt
Keyword(s):  
Ion Channel ◽  
Lipid Bilayers ◽  
Transient Receptor Potential ◽  
Single Channel ◽  
Applied Pressure ◽  
Mechanical Stimuli ◽  
Patch Clamp Technique ◽  
Open Probability ◽  
Pressure Interval

AbstractThe Transient Receptor Potential Ankyrin 1 (TRPA1) channel is an intrinsic chemo- and thermo-sensitive ion channel with distinct sensory signaling properties. Although a role of TRPA1 in mammalian mechanosensory transduction in vivo seems likely, it remains to be shown that TRPA1 has the inherent capability to respond to mechanical stimuli. Here we have used the patch-clamp technique to study the response of human purified TRPA1 (hTRPA1), reconstituted into artificial lipid bilayers, to changes in bilayer pressure. We report that hTRPA1 responded with increased single-channel open probability (Po) within the applied pressure interval of 7.5 to 60 mmHg with a half maximum Po (P50) value of 38.0 ± 2.3 mmHg. The Po value reached a maximum close to 1 (0.87 ± 0.02) at 60 mmHg. Within the same pressure interval, hTRPA1 without its N-terminal ankyrin repeat domain (Δ1-688 hTRPA1) responded fully opened (0.99 ± 0.01) at 60 mmHg and with a P50 value of 39.0 ± 1.1 mmHg. The pressure-evoked responses of hTRPA1 and Δ1-688 hTRPA1 at 45 mmHg were inhibited by the TRPA1 antagonist HC030031, and the activity of purified hTRPA1 at 45 mmHg was abolished by the thiol reducing agent tris(2-carboxyethyl)phosphine (TCEP). In conclusion, hTRPA1 is an inherent mechanosensitive ion channel gated by force-from-lipids. The hTRPA1 mechanosensitivity is dependent on the redox environment, and it is suggested that oxidative stress shifts hTRPA1 into a protein conformation sensitive to mechanical stimuli.

scholarly journals Progressive recruitment of distal MEC-4 channels determines touch response strength in C. elegans

2019 ◽  
Author(s):  
S. Katta ◽  
A. Sanzeni ◽  
A. Das ◽  
M. Vergassola ◽  
M.B. Goodman
Keyword(s):  
Temporal Dynamics ◽  
Mechanical Strain ◽  
Tissue Mechanics ◽  
Mechanical Stimuli ◽  
Patch Clamp Recording ◽  
Open Probability ◽  
C Elegans ◽  
Somatosensory Neurons ◽  
Touch Response

AbstractTouch deforms, or strains, the skin beyond the immediate point of contact. The spatiotemporal nature of the touch-induced strain fields depend on the mechanical properties of the skin and the tissues below. Somatosensory neurons that sense touch branch out within the skin and rely on a set of mechano-electrical transduction channels distributed within their dendrites to detect mechanical stimuli. Here, we sought to understand how tissue mechanics shape touch-induced mechanical strain across the skin over time and how individual channels located in different regions of the strain field contribute to the overall touch response. We leveraged C. elegans’ touch receptor neurons (TRNs) as a simple model amenable to in vivo whole-cell patch clamp recording and an integrated experimental-computational approach to dissect the mechanisms underlying the spatial and temporal dynamics that we observed. Consistent with the idea that strain is produced at a distance, we show that delivering strong stimuli outside the anatomical extent of the neuron is sufficient to evoke MRCs. The amplitude and kinetics of the MRCs depended on both stimulus displacement and speed. Finally, we found that the main factor responsible for touch sensitivity is the recruitment of progressively more distant channels by stronger stimuli, rather than modulation of channel open probability. This principle may generalize to somatosensory neurons with more complex morphologies.SummaryThrough experiment and simulation, Katta et al. reveal that pushing faster and deeper recruits more and more distant mechano-electrical transduction channels during touch. The net result is a dynamic receptive field whose size and shape depends on tissue mechanics, stimulus parameters, and channel distribution within sensory neurons.

scholarly journals Therapeutic inhibition of keratinocyte TRPV3 sensory channel by local anesthetic dyclonine

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Qiang Liu ◽  
Jin Wang ◽  
Xin Wei ◽  
Juan Hu ◽  
Conghui Ping ◽  
...  
Keyword(s):  
Transient Receptor Potential ◽  
Single Channel ◽  
Receptor Potential ◽  
Epidermal Keratinocytes ◽  
Transient Receptor Potential Vanilloid ◽  
Growth Disorders ◽  
Open Probability ◽  
Gain Of Function ◽  
Sensory Channel

The multimodal sensory channel transient receptor potential vanilloid-3 (TRPV3) is expressed in epidermal keratinocytes and implicated in chronic pruritus, allergy, and inflammation-related skin disorders. Gain-of-function mutations of TRPV3 cause hair growth disorders in mice and Olmsted Syndrome in human. We here report that mouse and human TRPV3 channel is targeted by the clinical medication dyclonine that exerts a potent inhibitory effect. Accordingly, dyclonine rescued cell death caused by gain-of-function TRPV3 mutations and suppressed pruritus symptoms in vivo in mouse model. At the single-channel level, dyclonine inhibited TRPV3 open probability but not the unitary conductance. By molecular simulations and mutagenesis, we further uncovered key residues in TRPV3 pore region that could toggle the inhibitory efficiency of dyclonine. The functional and mechanistic insights obtained on dyclonine-TRPV3 interaction will help to conceive updated therapeutics for skin inflammation.

scholarly journals Progressive recruitment of distal MEC-4 channels determines touch response strength in C. elegans

2019 ◽  
Vol 151 (10) ◽  
pp. 1213-1230 ◽  
Author(s):  
Samata Katta ◽  
Alessandro Sanzeni ◽  
Alakananda Das ◽  
Massimo Vergassola ◽  
Miriam B. Goodman
Keyword(s):  
Temporal Dynamics ◽  
Mechanical Strain ◽  
Response Strength ◽  
Tissue Mechanics ◽  
Mechanical Stimuli ◽  
Patch Clamp Recording ◽  
Open Probability ◽  
Somatosensory Neurons ◽  
Touch Response

Touch deforms, or strains, the skin beyond the immediate point of contact. The spatiotemporal nature of the touch-induced strain fields depend on the mechanical properties of the skin and the tissues below. Somatosensory neurons that sense touch branch out within the skin and rely on a set of mechano-electrical transduction channels distributed within their dendrites to detect mechanical stimuli. Here, we sought to understand how tissue mechanics shape touch-induced mechanical strain across the skin over time and how individual channels located in different regions of the strain field contribute to the overall touch response. We leveraged Caenorhabditis elegans’ touch receptor neurons as a simple model amenable to in vivo whole-cell patch-clamp recording and an integrated experimental-computational approach to dissect the mechanisms underlying the spatial and temporal dynamics we observed. Consistent with the idea that strain is produced at a distance, we show that delivering strong stimuli outside the anatomical extent of the neuron is sufficient to evoke MRCs. The amplitude and kinetics of the MRCs depended on both stimulus displacement and speed. Finally, we found that the main factor responsible for touch sensitivity is the recruitment of progressively more distant channels by stronger stimuli, rather than modulation of channel open probability. This principle may generalize to somatosensory neurons with more complex morphologies.

Mechanisms of Pi regulation of the skeletal muscle SR Ca2+ release channel

2000 ◽  
Vol 278 (3) ◽  
pp. C601-C611 ◽  
Author(s):  
Edward M. Balog ◽  
Bradley R. Fruen ◽  
Patricia K. Kane ◽  
Charles F. Louis
Keyword(s):  
Skeletal Muscle ◽  
Single Channel ◽  
Adenine Nucleotides ◽  
Muscle Fibers ◽  
Open Probability ◽  
Release Channel ◽  
High Concentrations ◽  
Channel Open Time ◽  
Stimulation Of

Inorganic phosphate (Pi) accumulates in the fibers of actively working muscle where it acts at various sites to modulate contraction. To characterize the role of Pi as a regulator of the sarcoplasmic reticulum (SR) calcium (Ca2+) release channel, we examined the action of Pi on purified SR Ca2+ release channels, isolated SR vesicles, and skinned skeletal muscle fibers. In single channel studies, addition of Pi to the cis chamber increased single channel open probability ( P o; 0.079 ± 0.020 in 0 Pi, 0.157 ± 0.034 in 20 mM Pi) by decreasing mean channel closed time; mean channel open times were unaffected. In contrast, the ATP analog, β,γ-methyleneadenosine 5′-triphosphate (AMP-PCP), enhanced P o by increasing single channel open time and decreasing channel closed time. Pi stimulation of [3H]ryanodine binding by SR vesicles was similar at all concentrations of AMP-PCP, suggesting Pi and adenine nucleotides act via independent sites. In skinned muscle fibers, 40 mM Pi enhanced Ca2+-induced Ca2+ release, suggesting an in situ stimulation of the release channel by high concentrations of Pi. Our results support the hypothesis that Pi may be an important endogenous modulator of the skeletal muscle SR Ca2+ release channel under fatiguing conditions in vivo, acting via a mechanism distinct from adenine nucleotides.

scholarly journals The development of cooperative channels explains the maturation of hair cell’s mechanotransduction

2019 ◽  
Author(s):  
Francesco Gianoli ◽  
Thomas Risler ◽  
Andrei S. Kozlov
Keyword(s):  
Ion Channels ◽  
Hair Cell ◽  
Inner Ear ◽  
Hair Cells ◽  
Hair Bundle ◽  
Mechanical Stimuli ◽  
Biophysical Properties ◽  
Tip Link ◽  
Fast Adaptation ◽  
Kinetics Of

ABSTRACTHearing relies on the conversion of mechanical stimuli into electrical signals. In vertebrates, this process of mechano-electrical transduction (MET) is performed by specialized receptors of the inner ear, the hair cells. Each hair cell is crowned by a hair bundle, a cluster of microvilli that pivot in response to sound vibrations, causing the opening and closing of mechanosensitive ion channels. Mechanical forces are projected onto the channels by molecular springs called tip links. Each tip link is thought to connect to a small number of MET channels that gate cooperatively and operate as a single transduction unit. Pushing the hair bundle in the excitatory direction opens the channels, after which they rapidly reclose in a process called fast adaptation. It has been experimentally observed that the hair cell’s biophysical properties mature gradually during postnatal development: the maximal transduction current increases, sensitivity sharpens, transduction occurs at smaller hair-bundle displacements, and adaptation becomes faster. Similar observations have been reported during tip-link regeneration after acoustic damage. Moreover, when measured at intermediate developmental stages, the kinetics of fast adaptation varies in a given cell depending on the magnitude of the imposed displacement. The mechanisms underlying these seemingly disparate observations have so far remained elusive. Here, we show that these phenomena can all be explained by the progressive addition of MET channels of constant properties, which populate the hair bundle first as isolated entities, then progressively as clusters of more sensitive, cooperative MET channels. As the proposed mechanism relies on the difference in biophysical properties between isolated and clustered channels, this work highlights the importance of cooperative interactions between mechanosensitive ion channels for hearing.SIGNIFICANCEHair cells are the sensory receptors of the inner ear that convert mechanical stimuli into electrical signals transmitted to the brain. Sensitivity to mechanical stimuli and the kinetics of mechanotransduction currents change during hair-cell development. The same trend, albeit on a shorter timescale, is also observed during hair-cell recovery from acoustic trauma. Furthermore, the current kinetics in a given hair cell depends on the stimulus magnitude, and the degree of that dependence varies with development. These phenomena have so far remained unexplained. Here, we show that they can all be reproduced using a single unifying mechanism: the progressive formation of channel pairs, in which individual channels interact through the lipid bilayer and gate cooperatively.

scholarly journals Exclusion of alternative exon 33 of CaV1.2 calcium channels in heart is proarrhythmogenic

2017 ◽  
Vol 114 (21) ◽  
pp. E4288-E4295 ◽  
Author(s):  
Guang Li ◽  
Juejin Wang ◽  
Ping Liao ◽  
Peter Bartels ◽  
Hengyu Zhang ◽  
...  
Keyword(s):  
Alternative Splicing ◽  
Calcium Channel ◽  
Single Channel ◽  
Heart Function ◽  
Alternative Exon ◽  
Electrophysiological Property ◽  
Open Probability ◽  
Premature Ventricular Contractions ◽  
Channel Function

Alternative splicing changes the CaV1.2 calcium channel electrophysiological property, but the in vivo significance of such altered channel function is lacking. Structure–function studies of heterologously expressed CaV1.2 channels could not recapitulate channel function in the native milieu of the cardiomyocyte. To address this gap in knowledge, we investigated the role of alternative exon 33 of the CaV1.2 calcium channel in heart function. Exclusion of exon 33 in CaV1.2 channels has been reported to shift the activation potential −10.4 mV to the hyperpolarized direction, and increased expression of CaV1.2Δ33 channels was observed in rat myocardial infarcted hearts. However, how a change in CaV1.2 channel electrophysiological property, due to alternative splicing, might affect cardiac function in vivo is unknown. To address these questions, we generated mCacna1c exon 33−/−-null mice. These mice contained CaV1.2Δ33 channels with a gain-of-function that included conduction of larger currents that reflects a shift in voltage dependence and a modest increase in single-channel open probability. This altered channel property underscored the development of ventricular arrhythmia, which is reflected in significantly more deaths of exon 33−/− mice from β-adrenergic stimulation. In vivo telemetric recordings also confirmed increased frequencies in premature ventricular contractions, tachycardia, and lengthened QT interval. Taken together, the significant decrease or absence of exon 33-containing CaV1.2 channels is potentially proarrhythmic in the heart. Of clinical relevance, human ischemic and dilated cardiomyopathy hearts showed increased inclusion of exon 33. However, the possible role that inclusion of exon 33 in CaV1.2 channels may play in the pathogenesis of human heart failure remains unclear.

Biophysical and pharmacological characterization of inwardly rectifying K+ currents in rat spinal cord astrocytes

1995 ◽  
Vol 73 (1) ◽  
pp. 333-346 ◽  
Author(s):  
C. B. Ransom ◽  
H. Sontheimer
Keyword(s):  
Spinal Cord ◽  
Single Channel ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Dependent Manner ◽  
Rat Spinal Cord ◽  
Open Probability ◽  
Kir Channels ◽  
Inwardly Rectifying ◽  
K Currents

1. Whole cell and cell-attached patch-clamp recordings were obtained from rat spinal cord astrocytes maintained in culture for 6-14 days. It was found that the resting conductance in these astrocytes is primarily due to inwardly rectifying K+ (Kir) channels. 2. Two types of astrocytic Kir channels were identified with single-channel conductances of approximately 28 and approximately 80 pS, respectively. Channels displayed some voltage dependence in their open probability, which was largest (0.8-0.9) near the K+ equilibrium potential (Ek) and decreased at more negative potentials. The resting potential closely followed Ek, so it can be assumed that Kir channels have a high open probability at the resting potential. 3. The conductance of inwardly rectifying K+ currents (Kir) depended strongly on [K+]o and was approximately proportional to the square-root of [K+]o. 4. Kir currents inactivated in a time- and voltage-dependent manner. The Na+ dependence of inactivation was studied with ion substitution experiments. Replacement of [Na+]o with choline or Li+ removed inactivation. This dependence of current inactivation on [Na+]o resembles the previously described block of Kir channels in other systems by [Na+]o. 5. Kir currents were also blocked in a dose-dependent manner by Cs+ (Kd = 189 microM at -140 mV), Ba2+ (Kd = 3.5 microM), and tetraethylammonium (TEA; 90% block at 10 mM) but were insensitive to 4-aminopyridine (4-AP; 5 mM). In the current-clamp mode, Ba2+ and TEA inhibition of Kir currents was associated with a marked depolarization, suggesting that Kir channel activity played a role in the establishment of the negative resting potential typical of astrocytes. 6. These biophysical features of astrocyte inwardly rectifying K+ channels are consistent with those properties required for their proposed involvement in [K+]o clearance: 1) high open probability at the resting potential, 2) increasing conductance with increasing [K+]o, and 3) rectification, e.g., channel closure, at positive potentials. It is proposed, therefore, that the dissipation of [K+]o following neuronal activity is mediated primarily by the activity of astrocytic Kir channels.

scholarly journals β-Adrenergic agonists differentially regulate highly selective and nonselective epithelial sodium channels to promote alveolar fluid clearance in vivo

2012 ◽  
Vol 302 (11) ◽  
pp. L1167-L1178 ◽  
Author(s):  
Charles A. Downs ◽  
Lisa H. Kriener ◽  
Ling Yu ◽  
Douglas C. Eaton ◽  
Lucky Jain ◽  
...  
Keyword(s):  
Single Channel ◽  
Selective Inhibition ◽  
Alveolar Epithelial Cells ◽  
Alveolar Type ◽  
Channel Measurements ◽  
Open Probability ◽  
Alveolar Epithelial ◽  
Lung Fluid ◽  
T1 And T2

β-Adrenergic receptors (β-AR) increase epithelial sodium channel (ENaC) activity to promote lung fluid clearance. However, the effect of selective β-AR agonist on highly selective cation (HSC) channels or nonselective cation (NSC) channels in alveolar type 1 (T1) and type 2 (T2) cells is unknown. We hypothesized that stimulation with β1-AR agonist (denopamine) or β2-AR agonist (terbutaline) would increase HSC and/or NSC channel activity in alveolar epithelial cells. We performed single-channel measurements from T1 and T2 cells accessed from rat lung slices. Terbutaline (20 μM) increased HSC ENaC activity (open probability, NPo) in T1 (from 0.96 ± 0.61 to 1.25 ± 0.71, n = 5, P <0.05) and T2 cells (from 0.28 ± 0.14 to 1.0 ± 0.30, n = 8, P = 0.02). Denopamine (20 μM) increased NSC NPo in T1 cells (from 0.34 ± 0.09 to 0.63 ± 0.14, n = 7, P = 0.02) and in T2 cells (from 0.47 ± 0.09 to 0.68 ± 0.10, P = 0.004). In vivo X-ray imaging of lung fluid clearance and ICI 118,551 selective inhibition of β2-ARs confirmed patch-clamp findings. cAMP concentrations increased following treatment with denopamine or terbutaline ( n = 3, P < 0.002). The effects of systemic (intraperitoneal, IP) and local (intratracheal, IT) modes of delivery on lung fluid clearance were assessed. IT delivery of denopamine promoted alveolar flooding, whereas IP delivery promoted delayed fluid clearance. In summary, β-AR agonists differentially regulate HSC and NSC in T1 and T2 cells to promote lung fluid clearance in vivo, and the mode of drug delivery is critical for maximizing β-AR agonist efficacy.

scholarly journals On the Interaction of Neomycin with the Slow Vacuolar Channel of Arabidopsis thaliana

2006 ◽  
Vol 127 (3) ◽  
pp. 329-340 ◽  
Author(s):  
Joachim Scholz-Starke ◽  
Armando Carpaneto ◽  
Franco Gambale
Keyword(s):  
Arabidopsis Thaliana ◽  
Single Channel ◽  
Aminoglycoside Antibiotic ◽  
Dependent Manner ◽  
Open Probability ◽  
Mesophyll Cells ◽  
Concentration Dependent Manner ◽  
Slow Vacuolar Channel ◽  
Sv Channel

This study investigates the interaction of the aminoglycoside antibiotic neomycin with the slow vacuolar (SV) channel in vacuoles from Arabidopsis thaliana mesophyll cells. Patch-clamp experiments in the excised patch configuration revealed a complex pattern of neomycin effects on the channel: applied at concentrations in the submicromolar to millimolar range neomycin (a) blocked macroscopic SV currents in a voltage- and concentration-dependent manner, (b) slowed down activation and deactivation kinetics of the channel, and most interestingly, (c) at concentrations above 10 μM, neomycin shifted the SV activation threshold towards negative membrane potentials, causing a two-phasic activation at high concentrations. Single channel experiments showed that neomycin causes these macroscopic effects by combining a decrease of the single channel conductance with a concomitant increase of the channel's open probability. Our results clearly demonstrate that the SV channel can be activated at physiologically relevant tonoplast potentials in the presence of an organic effector molecule. We therefore propose the existence of a cellular equivalent regulating the activity of the SV channel in vivo.

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