scholarly journals The speed of the hair cell mechanotransducer channel revealed by fluctuation analysis

2021 ◽  
Vol 153 (10) ◽  
Author(s):  
Maryline Beurg ◽  
Jong-Hoon Nam ◽  
Robert Fettiplace
Keyword(s):  
Time Constant ◽  
Single Channel ◽  
Noise Analysis ◽  
Outer Hair Cells ◽  
Fluctuation Analysis ◽  
Molecular Architecture ◽  
Activation Time ◽  
Channel Conductance ◽  
Pass Filter ◽  
Low Pass Filter

Although mechanoelectrical transducer (MET) channels have been extensively studied, uncertainty persists about their molecular architecture and single-channel conductance. We made electrical measurements from mouse cochlear outer hair cells (OHCs) to reexamine the MET channel conductance comparing two different methods. Analysis of fluctuations in the macroscopic currents showed that the channel conductance in apical OHCs determined from nonstationary noise analysis was about half that of single-channel events recorded after tip link destruction. We hypothesized that this difference reflects a bandwidth limitation in the noise analysis, which we tested by simulations of stochastic fluctuations in modeled channels. Modeling indicated that the unitary conductance depended on the relative values of the channel activation time constant and the applied low-pass filter frequency. The modeling enabled the activation time constant of the channel to be estimated for the first time, yielding a value of only a few microseconds. We found that the channel conductance, assayed with both noise and recording of single-channel events, was reduced by a third in a new deafness mutant, Tmc1 p.D528N. Our results indicate that noise analysis is likely to underestimate MET channel amplitude, which is better characterized from recordings of single-channel events.

Single-channel basis for conductance increase induced by isoflurane in Shaker H4 IR K+ channels

2001 ◽  
Vol 280 (5) ◽  
pp. C1130-C1139 ◽  
Author(s):  
Jichang Li ◽  
Ana M. Correa
Keyword(s):  
Time Course ◽  
Xenopus Oocytes ◽  
Single Channel ◽  
Noise Analysis ◽  
Single Channels ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Open Probability ◽  
Slowing Down ◽  
Conductance Increase

Volatile anesthetics modulate the function of various K+ channels. We previously reported that isoflurane induces an increase in macroscopic currents and a slowing down of current deactivation of Shaker H4 IR K+ channels. To understand the single-channel basis of these effects, we performed nonstationary noise analysis of macroscopic currents and analysis of single channels in patches from Xenopus oocytes expressing Shaker H4 IR. Isoflurane (1.2% and 2.5%) induced concentration-dependent, partially reversible increases in macroscopic currents and in the time course of tail currents. Noise analysis of currents (70 mV) revealed an increase in unitary current (∼17%) and maximum open probability (∼20%). Single-channel conductance was larger (∼20%), and opening events were more stable, in isoflurane. Tail-current slow time constants increased by 41% and 136% in 1.2% and 2.5% isoflurane, respectively. Our results show that, in a manner consistent with stabilization of the open state, isoflurane increased the macroscopic conductance of Shaker H4 IR K+ channels by increasing the single-channel conductance and the open probability.

scholarly journals Temperature dependence of ion permeation at the endplate channel.

1983 ◽  
Vol 81 (5) ◽  
pp. 687-703 ◽  
Author(s):  
H M Hoffmann ◽  
V E Dionne
Keyword(s):  
Free Energy ◽  
Single Channel ◽  
Ion Selectivity ◽  
Boltzmann Distribution ◽  
Type Model ◽  
Fluctuation Analysis ◽  
Ion Binding ◽  
Ion Permeation ◽  
Channel Conductance ◽  
Extracellular Side

The dependence of acetylcholine receptor mean single-channel conductance on temperature was studied at garter snake twitch-muscle endplates using fluctuation analysis. In normal saline under conditions where most of the endplate current was carried by Na+, the channel conductance increased continuously from near 0 degrees C to approximately 23 degrees C with a Q10 of 1.97 +/- 0.14 (mean +/- SD). When 50% of the bath Na+ was replaced by either Li+, Rb+, or Cs+, the Q10 did not change significantly; however, at any temperature the channel conductance was greatest in Cs-saline and decreased with the ion sequence Cs greater than Rb greater than Na greater than Li. The results were fit by an Eyring-type model consisting of one free-energy well on the extracellular side of a single energy barrier. Ion selectivity appeared to result from ion-specific differences in the well and not in the barrier of this model. With a constant barrier enthalpy for different ions, well free-energy depth was greatest for Cs+ and graded identical to the permeability sequence. The correlation between increased well depth (i.e., ion binding) and increased channel conductance can be accounted for by the Boltzmann distribution of thermal energy.

scholarly journals Mechanisms of activation and desensitization of full-length glycine receptor in membranes

2019 ◽  
Author(s):  
Arvind Kumar ◽  
Sandip Basak ◽  
Shanlin Rao ◽  
Yvonne Gicheru ◽  
Megan L. Mayer ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Single Channel ◽  
Glycine Receptor ◽  
Full Length ◽  
Structural Basis ◽  
Molecular Architecture ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
The Central Nervous System ◽  
Dynamics Simulations

AbstractGlycinergic synapses play a central role in motor control and pain processing in the central nervous system. Glycine receptors (GlyR) are key players in mediating fast inhibitory neurotransmission at these synapses. While previous high-resolution structural studies have provided insights into the molecular architecture of GlyR, several mechanistic questions pertaining to channel function are still unknown. Here, we present Cryo-EM structures of the full-length GlyR protein reconstituted into lipid nanodiscs that are captured in the unliganded (closed) and glycine-bound (open and desensitized) conformations. A comparison of the three states reveals global conformational changes underlying GlyR channel gating. The functional state assignments were validated by molecular dynamics simulations of the structures incorporated in a lipid bilayer. Observed permeation events are in agreement with the anion selectivity of the channel and the reported single-channel conductance of GlyR. These studies establish the structural basis for gating, selectivity, and single-channel conductance of GlyR in a physiological environment.

Frequency-domain characteristics and filtering of blood flow following the onset of exercise: implications for kinetics analysis

2006 ◽  
Vol 100 (3) ◽  
pp. 817-825 ◽  
Author(s):  
Leonardo F. Ferreira ◽  
Allison J. Harper ◽  
Thomas J. Barstow
Keyword(s):  
Blood Flow ◽  
Power Spectrum ◽  
Time Constant ◽  
Standard Error ◽  
Phase 1 ◽  
High Signal ◽  
Parameter Estimates ◽  
Phase 2 ◽  
Pass Filter ◽  
Low Pass Filter

We examined the validity and usefulness of a low-pass filter (LPFILTER) to reduce point-to-point variability and enhance parameter estimation of the kinetics of blood flow (BF). Computer simulations were used to determine the power spectrum of simulated responses. Moreover, we studied the leg BF response to a single transition in four subjects during supine knee-extension exercise using three methods of data processing [beat-by-beat, average of 3 cardiac cycles (AVG3 BEATS), and LPFILTER]. The power spectrum of BF containing the kinetics information (≤0.2 Hz) did not overlap with the oscillations due to muscle contraction and cardiac cycle (simulations and Doppler measurements). There were no significant differences between the parameter estimates for a two-exponential model using Beat-by-Beat, AVG3 BEATS, and LPFILTER ( P > 0.05; n = 4). However, LPFILTER (cutoff = 0.2 Hz) resulted in a significantly lower standard error of the estimate for all parameters ( P < 0.05). The means ± SD for the standard error of the estimate for Beat-by-Beat, AVG3 BEATS, and LPFILTER were, respectively, time constant- phase 1 = 5.0 ± 1.1 s, 4.5 ± 2.1 s, and 0.3 ± 0.2 s; time delay- phase 2 = 17.8 ± 7.9 s, 12.8 ± 7.5 s, and 1.4 ± 1.4 s; time constant- phase 2 = 15.8 ± 4.6 s, 9.9 ± 2.9 s, and 1.1 ± 0.5 s. In conclusion, LPFILTER appeared to be a valid procedure providing a high signal-to-noise ratio and data density and thus LPFILTER resulted in the smallest confidence interval for parameter estimates of BF kinetics.

Application of IMC-PID in the Hydraulic Headbox Total Pressure Control

2012 ◽  
Vol 462 ◽  
pp. 789-795
Author(s):  
Wei Tang ◽  
Xu Zhong Niu ◽  
Wen Juan Shan
Keyword(s):  
Control System ◽  
Time Constant ◽  
Total Pressure ◽  
Pressure Control ◽  
Internal Model Control ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Model Control ◽  
Low Pass ◽  
Pressure Control System

It is very difficult to obtain perfect performance to apply the conventional PID (Proportional-Integral-Derivative) controller, because hydraulic headbox needs high precision total pressure control. Transfer function of total pressure control system was identified by using the direct identification method which is based on the least square method for the first-order plus delay time model. Then combined with IMC (Internal-Model-control) –PID method, an IMC-PID controller was designed, which is simple and only needed to adjust one parameter-the time constant of low pass filter. Acceptable performance can also be obtained by tuning time constant of the low pass filter when the model doesn't match with the real process. The algorithm was applied to total pressure control system of hydraulic headbox. Simulation and practical application show that, IMC-PID is of strong robustness and good dynamic characteristics. Finally, the control system is implemented by S7-300 PLC.

scholarly journals Basolateral K channels in an insect epithelium. Channel density, conductance, and block by barium.

1986 ◽  
Vol 87 (3) ◽  
pp. 443-466 ◽  
Author(s):  
J W Hanrahan ◽  
N K Wills ◽  
J E Phillips ◽  
S A Lewis
Keyword(s):  
Single Channel ◽  
Short Circuit ◽  
Noise Analysis ◽  
Basolateral Membrane ◽  
Membrane Conductance ◽  
Short Circuit Current ◽  
Corner Frequency ◽  
Fluctuation Analysis ◽  
K Channels ◽  
K Current

K channels in the basolateral membrane of insect hindgut were studied using current fluctuation analysis and microelectrodes. Locust recta were mounted in Ussing-type chambers containing Cl-free saline and cyclic AMP (cAMP). A transepithelial K current was induced by raising serosal [K] under short-circuit conditions. Adding Ba to the mucosal (luminal) side under these conditions had no effect; however, serosal Ba reversibly inhibited the short-circuit current (Isc), increased transepithelial resistance (Rt), and added a Lorentzian component to power density spectra of the Isc. A nonlinear relationship between corner frequency and serosal [Ba] was observed, which suggests that the rate constant for Ba association with basolateral channels increased as [Ba] was elevated. Microelectrode experiments revealed that the basolateral membrane hyperpolarized when Ba was added: this change in membrane potential could explain the nonlinearity of the 2 pi fc vs. [Ba] relationship if external Ba sensed about three-quarters of the basolateral membrane field. Conventional microelectrodes were used to determine the correspondence between transepithelially measured current noise and basolateral membrane conductance fluctuations, and ion-sensitive microelectrodes were used to measure intracellular K activity (acK). From the relationship between the net electrochemical potential for K across the basolateral membrane and the single channel current calculated from noise analysis, we estimate that the conductance of basolateral K channels is approximately 60 pS, and that there are approximately 180 million channels per square centimeter of tissue area.

Differentiation of NG108-15 cells alters channel conductance and desensitization kinetics of the 5-HT3 receptor

1991 ◽  
Vol 65 (3) ◽  
pp. 630-638 ◽  
Author(s):  
X. M. Shao ◽  
J. L. Yakel ◽  
M. B. Jackson
Keyword(s):  
Single Channel ◽  
Noise Analysis ◽  
Morphological Differentiation ◽  
Culture Conditions ◽  
Receptor Subtypes ◽  
Channel Conductance ◽  
Differentiated Cells ◽  
Undifferentiated Cells ◽  
Current Voltage Curve ◽  
Single Channel Currents

1. NG108-15 cells undergo morphological differentiation in response to appropriate culture conditions. We have used patch clamp techniques to compare responses mediated by the 5-HT3 receptor in differentiated and undifferentiated NG108-15 cells. 2. In differentiated cells, desensitization of 5-hydroxytryptamine (5-HT) responses was much slower than in undifferentiated cells. Desensitization in differentiated cells was also highly variable, with half-times varying by greater than 40-fold. Rapidly desensitized responses in differentiated cells were qualitatively similar to the responses of undifferentiated cells. 3. In outside-out patches from undifferentiated cells, single channel currents could be seen after 5-HT application. These channels had a conductance of 12 pS. The 5-HT-activated channels in differentiated cells were too small to observe at the single-channel level. Noise analysis indicated that the channel conductance was approximately 4 pS. In differentiated cells, both rapidly and slowly desensitized responses were generated by channels with essentially the same conductance. 4. The 5-HT responses of differentiated cells were also distinguished from those of undifferentiated cells on the basis of the voltage dependence of desensitization and the curvature of the current-voltage curve. 5. NG108-15 cells can produce different receptor subtypes, which may be expressed in different tissues or at different stages of development. These variations in receptor behavior suggest that there are at least two distinct mechanisms for regulation of the 5-HT3 receptor.

Activation of NMDA Receptors in Rat Dentate Gyrus Granule Cells by Spontaneous and Evoked Transmitter Release

2003 ◽  
Vol 90 (2) ◽  
pp. 786-797 ◽  
Author(s):  
Nils Ole Dalby ◽  
Istvan Mody
Keyword(s):  
Nmda Receptor ◽  
Dentate Gyrus ◽  
Nmda Receptors ◽  
Granule Cells ◽  
Single Channel ◽  
Complex Mixture ◽  
Fluctuation Analysis ◽  
Channel Conductance ◽  
Single Channel Conductance ◽  
Current Shift

Activation of N-methyl-d-aspartate (NMDA) receptors by synaptically released glutamate in the nervous system is usually studied using evoked events mediated by a complex mixture of AMPA, kainate, and NMDA receptors. Here we have characterized pharmacologically isolated spontaneous NMDA receptor-mediated synaptic events and compared them to stimulus evoked excitatory postsynaptic currents (EPSCs) in the same cell to distinguish between various modes of activation of NMDA receptors. Spontaneous NMDA receptor-mediated EPSCs recorded at 34°C in dentate gyrus granule cells (DGGC) have a frequency of 2.5 ± 0.3 Hz and an average peak amplitude of 13.2 ± 0.8 pA, a 10–90% rise time of 5.4 ± 0.3 ms, and a decay time constant of 42.1 ± 2.1 ms. The single-channel conductance estimated by nonstationary fluctuation analysis was 60 ± 5 pS. The amplitudes (46.5 ± 6.4 pA) and 10–90% rise times (18 ± 2.3 ms) of EPSCs evoked from the entorhinal cortex/subiculum border are significantly larger than the same parameters for spontaneous events (paired t-test, P < 0.05, n = 17). Perfusion of 50 μM d(–)-2-amino-5-phosphonopentanoic acid blocked all spontaneous activity and caused a significant baseline current shift of 18.8 ± 3.0 pA, thus identifying a tonic conductance mediated by NMDA receptors. The NR2B antagonist ifenprodil (10 μM) significantly reduced the frequency of spontaneous events but had no effect on their kinetics or on the baseline current or variance. At the same time, the peak current and charge of stimulus-evoked events were significantly diminished by ifenprodil. Thus spontaneous NMDA receptor-mediated events in DGGC are predominantly mediated by NR2A or possibly NR2A/NR2B receptors while the activation of NR2B receptors reduces the excitability of entorhinal afferents either directly or through an effect on the entorhinal cells.

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