Measuring the Kinetics of Ion Permeation in Low Conductance 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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Extraction of Auditory Information by Modulation of Neuronal Ion Channels

The Oxford Handbook of the Auditory Brainstem ◽

10.1093/oxfordhb/9780190849061.013.23 ◽

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.

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Insights into the biophysical properties of GABAA ion channels: Modulation of ion permeation by drugs and protein interactions

Biochimica et Biophysica Acta (BBA) - Biomembranes ◽

10.1016/j.bbamem.2010.11.022 ◽

2011 ◽

Vol 1808 (3) ◽

pp. 667-673 ◽

Cited By ~ 9

Author(s):

M. Louise Tierney

Keyword(s):

Ion Channels ◽

Protein Interactions ◽

Ion Permeation ◽

Biophysical Properties

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Ion Channel Permeation and Selectivity

The Oxford Handbook of Neuronal Ion Channels ◽

10.1093/oxfordhb/9780190669164.013.22 ◽

2019 ◽

Author(s):

Juan J. Nogueira ◽

Ben Corry

Keyword(s):

Ion Channels ◽

Ion Channel ◽

Ion Selectivity ◽

Ionic Currents ◽

Biological Processes ◽

Ion Permeation ◽

Voltage Gated ◽

Physical Mechanisms ◽

Theoretical Approaches ◽

Mechanistic Insight

Many biological processes essential for life rely on the transport of specific ions at specific times across cell membranes. Such exquisite control of ionic currents, which is regulated by protein ion channels, is fundamental for the proper functioning of the cells. It is not surprising, therefore, that the mechanism of ion permeation and selectivity in ion channels has been extensively investigated by means of experimental and theoretical approaches. These studies have provided great mechanistic insight but have also raised new questions that are still unresolved. This chapter first summarizes the main techniques that have provided significant knowledge about ion permeation and selectivity. It then discusses the physical mechanisms leading to ion permeation and the explanations that have been proposed for ion selectivity in voltage-gated potassium, sodium, and calcium channels.

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The M2 transmembrane segment as a molecular determinant of the ion permeation properties in the superfamily of ligand-gated ion channels

Biochemical Society Transactions ◽

10.1042/bst022382s ◽

1994 ◽

Vol 22 (3) ◽

pp. 382S-382S ◽

Cited By ~ 2

Author(s):

ANTONIO V. FERRER-MONTIEL ◽

CRAIG D. PATTEN ◽

WILLIAM SUN ◽

JARAD SCHIFFER ◽

MAURICIO MONTAL

Keyword(s):

Ion Channels ◽

Ion Permeation ◽

Transmembrane Segment ◽

Molecular Determinant ◽

Permeation Properties ◽

Gated Ion Channels ◽

Ligand Gated Ion Channels

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

Faraday Discussions ◽

10.1039/a809608b ◽

1999 ◽

Vol 111 ◽

pp. 247-258 ◽

Cited By ~ 21

Author(s):

Gillian E. Woodhouse ◽

Lionel G. King ◽

Lech Wieczorek ◽

Bruce A. Cornell

Keyword(s):

Ion Channels ◽

Competitive Response ◽

Kinetics Of

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

Scientific Reports ◽

10.1038/srep32918 ◽

2016 ◽

Vol 6 (1) ◽

Cited By ~ 11

Author(s):

Alistair G. Fryatt ◽

Sudad Dayl ◽

Paul M. Cullis ◽

Ralf Schmid ◽

Richard J. Evans

Keyword(s):

Ion Channels ◽

Conformational Changes ◽

Kinetics Of

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A generalized kinetic model describes ion-permeation mechanisms in various ion channels

10.1101/2021.05.08.443239 ◽

2021 ◽

Author(s):

Di Wu

Keyword(s):

Ion Channels ◽

Kinetic Model ◽

Patch Clamp ◽

Cellular Responses ◽

Ion Permeation ◽

Patch Clamp Recording ◽

Boltzmann Factor ◽

Current Voltage ◽

Test Voltage ◽

Generalized Kinetic Model

Ion channels conduct various ions across biological membranes to maintain the membrane potential, to transmit the electrical signals, and to elicit the subsequent cellular responses by the signaling ions. Ion channels differ in their capabilities to select and conduct ions, which can be studied by the patch-clamp recording method that compares the current traces responding to the test voltage elicited at different conditions. In these experiments, the current-voltage curves are usually fitted by a sigmoidal function containing the Boltzmann factor. This equation is quite successful in fitting the experimental data in many cases, but it also fails in several others. Regretfully, some useful information may be lost in these data, which otherwise can reveal the ion-permeation mechanisms. Here we present a generalized kinetic model that captures the essential features of the current-voltage relations and describes the simple mechanism of the ion permeation through different ion channels. We demonstrate that this model is capable to fit various types of the patch-clamp data and explain their ion-permeation mechanisms.

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Identification of TMEM206 proteins as pore of PAORAC/ASOR acid-sensitive chloride channels

eLife ◽

10.7554/elife.49187 ◽

2019 ◽

Vol 8 ◽

Cited By ~ 10

Author(s):

Florian Ullrich ◽

Sandy Blin ◽

Katina Lazarow ◽

Tony Daubitz ◽

Jens Peter von Kries ◽

...

Keyword(s):

Cell Death ◽

Plasma Membrane ◽

Ion Channels ◽

Gene Family ◽

Chloride Channels ◽

Anion Channel ◽

Ion Permeation ◽

Acid Sensing Ion Channels ◽

Genome Wide ◽

A Genome

Acid-sensing ion channels have important functions in physiology and pathology, but the molecular composition of acid-activated chloride channels had remained unclear. We now used a genome-wide siRNA screen to molecularly identify the widely expressed acid-sensitive outwardly-rectifying anion channel PAORAC/ASOR. ASOR is formed by TMEM206 proteins which display two transmembrane domains (TMs) and are expressed at the plasma membrane. Ion permeation-changing mutations along the length of TM2 and at the end of TM1 suggest that these segments line ASOR’s pore. While not belonging to a gene family, TMEM206 has orthologs in probably all vertebrates. Currents from evolutionarily distant orthologs share activation by protons, a feature essential for ASOR’s role in acid-induced cell death. TMEM206 defines a novel class of ion channels. Its identification will help to understand its physiological roles and the diverse ways by which anion-selective pores can be formed.

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Conserved His-Gly motif of acid-sensing ion channels resides in a reentrant ‘loop’ implicated in gating and ion selectivity

10.1101/2020.03.02.974154 ◽

2020 ◽

Cited By ~ 1

Author(s):

Nate Yoder ◽

Eric Gouaux

Keyword(s):

Ion Channels ◽

Ion Selectivity ◽

Fear Memory ◽

Amino Terminus ◽

Ion Permeation ◽

Structural Explanation ◽

Cryo Electron Microscopy ◽

Acid Sensing Ion Channels ◽

And Function

ABSTRACTAcid-sensing ion channels (ASICs) are proton-gated members of the epithelial sodium channel/degenerin (ENaC/DEG) superfamily of ion channels and are expressed throughout central and peripheral nervous systems. The homotrimeric splice variant ASIC1a has been implicated in nociception, fear memory, mood disorders and ischemia. Here we extract full-length chicken ASIC1a (cASIC1a) from cell membranes using styrene maleic acid (SMA) copolymer, yielding structures of ASIC1a channels in both high pH resting and low pH desensitized conformations by single-particle cryo-electron microscopy (cryo-EM). The structures of resting and desensitized channels reveal a reentrant loop at the amino terminus of ASIC1a that includes the highly conserved ‘His-Gly’ (HG) motif. The reentrant loop lines the lower ion permeation pathway and buttresses the ‘Gly-Ala-Ser’ (GAS) constriction, thus providing a structural explanation for the role of the His-Gly dipeptide in the structure and function of ASICs.

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