Kinetics of the competitive response of receptors immobilised to ion-channels which have been incorporated into a tethered bilayer

1999 ◽  
Vol 111 ◽  
pp. 247-258 ◽  
Author(s):  
Gillian E. Woodhouse ◽  
Lionel G. King ◽  
Lech Wieczorek ◽  
Bruce A. Cornell
Keyword(s):  
Ion Channels ◽  
Competitive Response ◽  
Kinetics Of

Extraction of Auditory Information by Modulation of Neuronal Ion Channels

2018 ◽  
pp. 272-300
Author(s):  
Leonard K. Kaczmarek
Keyword(s):  
Ion Channels ◽  
Neuronal Firing ◽  
Auditory Information ◽  
Auditory Neurons ◽  
Complex Sound ◽  
Medial Nucleus ◽  
Rapid Changes ◽  
Genes Encoding ◽  
Kinetics Of ◽  
Trapezoid Body

All neurons express a subset of over seventy genes encoding potassium channel subunits. These channels have been studied in auditory neurons, particularly in the medial nucleus of the trapezoid body. The amplitude and kinetics of various channels in these neurons can be modified by the auditory environment. It has been suggested that such modulation is an adaptation of neuronal firing patterns to specific patterns of auditory inputs. Alternatively, such modulation may allow a group of neurons, all expressing the same set of channels, to represent a variety of responses to the same pattern of incoming stimuli. Such diversity would ensure that a small number of genetically identical neurons could capture and encode many aspects of complex sound, including rapid changes in timing and amplitude. This review covers the modulation of ion channels in the medial nucleus of the trapezoid body and how it may maximize the extraction of auditory information.All neurons express a subset of over seventy genes encoding potassium channel subunits. These channels have been studied in auditory neurons, particularly in the medial nucleus of the trapezoid body. The amplitude and kinetics of various channels in these neurons can be modified by the auditory environment. It has been suggested that such modulation is an adaptation of neuronal firing patterns to specific patterns of auditory inputs. Alternatively, such modulation may allow a group of neurons, all expressing the same set of channels, to represent a variety of responses to the same pattern of incoming stimuli. Such diversity would ensure that a small number of genetically identical neurons could capture and encode many aspects of complex sound, including rapid changes in timing and amplitude. This review covers the modulation of ion channels in the medial nucleus of the trapezoid body and how it may maximize the extraction of auditory information.

scholarly journals Mechanistic insights from resolving ligand-dependent kinetics of conformational changes at ATP-gated P2X1R ion channels

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Alistair G. Fryatt ◽  
Sudad Dayl ◽  
Paul M. Cullis ◽  
Ralf Schmid ◽  
Richard J. Evans
Keyword(s):  
Ion Channels ◽  
Conformational Changes ◽  
Kinetics Of

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 Kramers’ Diffusion Theory Applied to Gating Kinetics of Voltage-Dependent Ion Channels

1999 ◽  
Vol 76 (2) ◽  
pp. 782-803 ◽  
Author(s):  
Daniel Sigg ◽  
Hong Qian ◽  
Francisco Bezanilla
Keyword(s):  
Ion Channels ◽  
Diffusion Theory ◽  
Gating Kinetics ◽  
Voltage Dependent ◽  
Kinetics Of

scholarly journals Measuring the Kinetics of Ion Permeation in Low Conductance Ion Channels

2018 ◽  
Vol 114 (3) ◽  
pp. 546a
Author(s):  
Neville P. Bethel ◽  
Sara Capponi ◽  
John M. Rosenberg ◽  
Michael Grabe
Keyword(s):  
Ion Channels ◽  
Ion Permeation ◽  
Kinetics Of

Slow Photo-Cross-Linking Kinetics of Benzophenone-Labeled Voltage Sensors of Ion Channels†

Biochemistry ◽  
2001 ◽  
Vol 40 (35) ◽  
pp. 10707-10716 ◽  
Author(s):  
Shinghua Ding ◽  
Richard Horn
Keyword(s):  
Ion Channels ◽  
Cross Linking ◽  
Voltage Sensors ◽  
Kinetics Of

scholarly journals Voltage-dependence of Ion Permeation in Cyclic GMP–gated Ion Channels Is Optimized for Cell Function in Rod and Cone Photoreceptors

2002 ◽  
Vol 119 (4) ◽  
pp. 341-354 ◽  
Author(s):  
Tsuyoshi Ohyama ◽  
Arturo Picones ◽  
Juan I. Korenbrot
Keyword(s):  
Ion Channels ◽  
Cyclic Nucleotide ◽  
Time Course ◽  
Cell Function ◽  
Membrane Voltage ◽  
Rate Theory ◽  
Ion Permeation ◽  
Voltage Range ◽  
Kinetics Of ◽  
Gated Ion Channels

The kinetics of the photocurrent in both rod and cone retinal photoreceptors are independent of membrane voltage over the physiological range (−30 to −65 mV). This is surprising since the photocurrent time course is regulated by the influx of Ca2+ through cGMP-gated ion channels (CNG) and the force driving this flux changes with membrane voltage. To understand this paradigm, we measured Pf, the fraction of the cyclic nucleotide–gated current specifically carried by Ca2+ in intact, isolated photoreceptors. To measure Pf we activated CNG channels by suddenly increasing free 8-Br-cGMP in the cytoplasm of rods or cones loaded with a caged ester of the cyclic nucleotide. Simultaneous with the uncaging flash, we measured the cyclic nucleotide–dependent changes in membrane current and fluorescence of the Ca2+ binding dye, Fura-2, also loaded into the cells. We determined Pf under physiological solutions at various holding membrane voltages between −65 and −25 mV. Pf is larger in cones than in rods, but in both photoreceptor types its value is independent of membrane voltage over the range tested. This biophysical feature of the CNG channels offers a functional advantage since it insures that the kinetics of the phototransduction current are controlled by light, and not by membrane voltage. To explain our observation, we developed a rate theory model of ion permeation through CNG channels that assumes the existence of two ion binding sites within the permeation pore. To assign values to the kinetic rates in the model, we measured experimental I-V curves in membrane patches of rods and cones over the voltage range −90 to 90 mV in the presence of simple biionic solutions at different concentrations. We optimized the fit between simulated and experimental data. Model simulations describe well experimental photocurrents measured under physiological solutions in intact cones and are consistent with the voltage-independence of Pf, a feature that is optimized for the function of the channel in photoreceptors.

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