Superposition properties of independent ion channels

Membrane patches usually contain several ion channels of a given type. However, most of the stochastic modelling on which data analysis (in particular, estimation of kinetic constants) is currently based, relates to a single channel rather than to multiple channels. Attempts to circumvent this problem experimentally by recording under conditions where channel activity is low are restrictive and can introduce bias; moreover, possibly important information on how multichannel systems behave will be missed. We have extended existing theory to multichannel systems by applying results from point process theory to derive some distributional properties of the various types of sojourn time that occur when a given number of channels are open in a system containing a specified number of independent channels in equilibrium. Separate development of properties of a single channel and the superposition of several such independent channels simplifies the presentation of known results and extensions. To illustrate the general theory, particular attention is given to the types of sojourn time that occur in a two channel system; detailed expressions are presented for a selection of models, both Markov and non-Markov.

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TOK Homologue in Neurospora crassa: First Cloning and Functional Characterization of an Ion Channel in a Filamentous Fungus

Eukaryotic Cell ◽

10.1128/ec.2.1.181-190.2003 ◽

2003 ◽

Vol 2 (1) ◽

pp. 181-190 ◽

Cited By ~ 14

Author(s):

Stephen K. Roberts

Keyword(s):

Ion Channels ◽

Ion Channel ◽

Neurospora Crassa ◽

Filamentous Fungus ◽

Single Channel ◽

Functional Characterization ◽

Reversal Potential ◽

Channel Activity ◽

Biophysical Properties ◽

Patch Clamp Technique

ABSTRACT In contrast to animal and plant cells, very little is known of ion channel function in fungal physiology. The life cycle of most fungi depends on the “filamentous” polarized growth of hyphal cells; however, no ion channels have been cloned from filamentous fungi and comparatively few preliminary recordings of ion channel activity have been made. In an attempt to gain an insight into the role of ion channels in fungal hyphal physiology, a homolog of the yeast K+ channel (ScTOK1) was cloned from the filamentous fungus, Neurospora crassa. The patch clamp technique was used to investigate the biophysical properties of the N. crassa K+ channel (NcTOKA) after heterologous expression of NcTOKA in yeast. NcTOKA mediated mainly time-dependent outward whole-cell currents, and the reversal potential of these currents indicated that it conducted K+ efflux. NcTOKA channel gating was sensitive to extracellular K+ such that channel activation was dependent on the reversal potential for K+. However, expression of NcTOKA was able to overcome the K+ auxotrophy of a yeast mutant missing the K+ uptake transporters TRK1 and TRK2, suggesting that NcTOKA also mediated K+ influx. Consistent with this, close inspection of NcTOKA-mediated currents revealed small inward K+ currents at potentials negative of EK. NcTOKA single-channel activity was characterized by rapid flickering between the open and closed states with a unitary conductance of 16 pS. NcTOKA was effectively blocked by extracellular Ca2+, verapamil, quinine, and TEA+ but was insensitive to Cs+, 4-aminopyridine, and glibenclamide. The physiological significance of NcTOKA is discussed in the context of its biophysical properties.

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Statistical analysis of modal gating in ion channels

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2014.0030 ◽

2014 ◽

Vol 470 (2166) ◽

pp. 20140030 ◽

Cited By ~ 8

Author(s):

Ivo Siekmann ◽

James Sneyd ◽

Edmund J. Crampin

Keyword(s):

Ion Channels ◽

Single Channel ◽

Channel Activity ◽

Experimental Conditions ◽

Inositol Trisphosphate Receptor ◽

Statistical Framework ◽

Modal Gating ◽

Opening And Closing ◽

Trisphosphate Receptor ◽

Different Levels

Ion channels regulate the concentrations of ions within cells. By stochastically opening and closing its pore, they enable or prevent ions from crossing the cell membrane. However, rather than opening with a constant probability, many ion channels switch between several different levels of activity even if the experimental conditions are unchanged. This phenomenon is known as modal gating: instead of directly adapting its activity, the channel seems to mix sojourns in active and inactive modes in order to exhibit intermediate open probabilities. Evidence is accumulating that modal gating rather than modulation of opening and closing at a faster time scale is the primary regulatory mechanism of ion channels. However, currently, no method is available for reliably calculating sojourns in different modes. In order to address this challenge, we develop a statistical framework for segmenting single-channel datasets into segments that are characteristic for particular modes. The algorithm finds the number of mode changes, detects their locations and infers the open probabilities of the modes. We apply our approach to data from the inositol-trisphosphate receptor. Based upon these results, we propose that mode changes originate from alternative conformational states of the channel protein that determine a certain level of channel activity.

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Unsupervised idealization of ion channel recordings by Minimum Description Length: Application to human PIEZO1-channels

10.1101/106187 ◽

2017 ◽

Author(s):

Radhakrishnan Gnanasambandam ◽

Morten Schak Nielsen ◽

Christopher Nicolai ◽

Frederick Sachs ◽

Johannes Pauli Hofgaard ◽

...

Keyword(s):

Ion Channels ◽

Ion Channel ◽

Markov Models ◽

Single Channel ◽

Minimum Description Length ◽

Simulated Data ◽

Multiple Channels ◽

Electrophysiological Recordings ◽

Single Channel Currents ◽

Channel Currents

AbstractResearchers can investigate the mechanistic and molecular basis of many physiological phenomena in cells by analyzing the fundamental properties of single ion channels. These analyses entail recording single channel currents and measuring current amplitudes and transition rates between conductance states. Since most electrophysiological recordings contain noise, the data analysis can proceed by idealizing the recordings to isolate the true currents from the noise. This de-noising can be accomplished with threshold crossing algorithms and Hidden Markov Models, but such procedures generally depend on inputs and supervision by the user, thus requiring some prior knowledge of underlying processes. Channels with unknown gating and/or functional sub-states and the presence in the recording of currents from uncorrelated background channels present substantial challenges to unsupervised analyses.Here we describe and characterize an idealization algorithm based on Rissanen’s Minimum Description Length (MDL) Principle. This method uses minimal assumptions and idealizes ion channel recordings without requiring a detailed user input or a priori assumptions about channel conductance and kinetics.. Furthermore, we demonstrate that correlation analysis of conductance steps can resolve properties of single ion channels in recordings contaminated by signals from multiple channels. We first validated our methods on simulated data defined with a range of different signal-to-noise levels, and then showed that our algorithm can recover channel currents and their substates from recordings with multiple channels, even under conditions of high noise. We then tested the MDL algorithm on real experimental data from human PIEZO1 channels and found that our method revealed the presence of substates with alternate conductances.

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COMMUNICATION OF COMMON AND MARGINAL CHARACTERISTICS OF CONDITIONS IN A TWO-CHANNEL SYSTEM WITH SIMPLE STREAMLINES OF APPLICATIONS

VESTNIK OF ASTRAKHAN STATE TECHNICAL UNIVERSITY SERIES MANAGEMENT COMPUTER SCIENCE AND INFORMATICS ◽

10.24143/2072-9502-2017-3-7-19 ◽

2017 ◽

pp. 7-19 ◽

Cited By ~ 1

Author(s):

Georgiy Aleksandrovich Popov

Keyword(s):

Operating Systems ◽

Queue Length ◽

Recurrence Relations ◽

Queuing Systems ◽

Channel System ◽

Current Period ◽

Multichannel Systems ◽

Incoming Call ◽

Marginal Values ◽

Time Required

The article deals with a two-channel queuing system with a Poisson incoming call flow, in which the application processing time on each of the devices is different. Such models are used, in particular, when describing the operation of the system for selecting service requests in a number of operating systems. A complex system characteristic was introduced at the time of service endings on at least one of the devices, including the queue length, the remaining service time on the occupied device, and the time since the beginning of the current period of employment. This characteristic determines the state of the system at any time. Recurrence relations are obtained that connect this characteristic with its marginal values when there is no queue in the system. The method of introducing additional events was chosen as one of the main methods for analyzing the model. The relationships presented in this article can be used for analysis of the average characteristics of this system, as well as in the process of its simulation. Summarizing the results of work on multichannel systems with an arbitrary number of servicing devices will significantly reduce the time required for simulating complex systems described by sets of multichannel queuing systems.

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Autocrine‐Based Selection of Drugs That Target Ion Channels from Combinatorial Venom Peptide Libraries

Angewandte Chemie International Edition ◽

10.1002/anie.201603052 ◽

2016 ◽

Vol 55 (32) ◽

pp. 9306-9310 ◽

Cited By ~ 7

Author(s):

Hongkai Zhang ◽

Mingjuan Du ◽

Jia Xie ◽

Xiao Liu ◽

Jingying Sun ◽

...

Keyword(s):

Ion Channels ◽

Peptide Libraries ◽

Venom Peptide ◽

Selection Of

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Membrane-delimited Inhibition of Maxi-K Channel Activity by the Intermediate Conductance Ca2+-activated K Channel

The Journal of General Physiology ◽

10.1085/jgp.200509457 ◽

2006 ◽

Vol 127 (2) ◽

pp. 159-169 ◽

Cited By ~ 29

Author(s):

Jill Thompson ◽

Ted Begenisich

Keyword(s):

Single Channel ◽

Expression System ◽

Chemical Activation ◽

K Channel ◽

Channel Activity ◽

Single Family ◽

Open Probability ◽

K Channels ◽

Channel Proteins ◽

K Activity

The complexity of mammalian physiology requires a diverse array of ion channel proteins. This diversity extends even to a single family of channels. For example, the family of Ca2+-activated K channels contains three structural subfamilies characterized by small, intermediate, and large single channel conductances. Many cells and tissues, including neurons, vascular smooth muscle, endothelial cells, macrophages, and salivary glands express more than a single class of these channels, raising questions about their specific physiological roles. We demonstrate here a novel interaction between two types of Ca2+-activated K channels: maxi-K channels, encoded by the KCa1.1 gene, and IK1 channels (KCa3.1). In both native parotid acinar cells and in a heterologous expression system, activation of IK1 channels inhibits maxi-K activity. This interaction was independent of the mode of activation of the IK1 channels: direct application of Ca2+, muscarinic receptor stimulation, or by direct chemical activation of the IK1 channels. The IK1-induced inhibition of maxi-K activity occurred in small, cell-free membrane patches and was due to a reduction in the maxi-K channel open probability and not to a change in the single channel current level. These data suggest that IK1 channels inhibit maxi-K channel activity via a direct, membrane-delimited interaction between the channel proteins. A quantitative analysis indicates that each maxi-K channel may be surrounded by four IK1 channels and will be inhibited if any one of these IK1 channels opens. This novel, regulated inhibition of maxi-K channels by activation of IK1 adds to the complexity of the properties of these Ca2+-activated K channels and likely contributes to the diversity of their functional roles.

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Autocrine‐Based Selection of Drugs That Target Ion Channels from Combinatorial Venom Peptide Libraries

Angewandte Chemie ◽

10.1002/ange.201603052 ◽

2016 ◽

Vol 128 (32) ◽

pp. 9452-9456

Author(s):

Hongkai Zhang ◽

Mingjuan Du ◽

Jia Xie ◽

Xiao Liu ◽

Jingying Sun ◽

...

Keyword(s):

Ion Channels ◽

Peptide Libraries ◽

Venom Peptide ◽

Selection Of

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ATP mediates both activation and inhibition of K(ATP) channel activity via cAMP-dependent protein kinase in insulin-secreting cell lines.

The Journal of General Physiology ◽

10.1085/jgp.94.4.693 ◽

1989 ◽

Vol 94 (4) ◽

pp. 693-717 ◽

Cited By ~ 49

Author(s):

B Ribalet ◽

S Ciani ◽

G T Eddlestone

Keyword(s):

Protein Kinase ◽

Kinase Inhibitor ◽

Single Channel ◽

K Channel ◽

Channel Activity ◽

Dependent Protein Kinase ◽

Camp Dependent Protein Kinase ◽

Insulin Secreting Cells ◽

Dependent Protein ◽

Inside Out

The single-channel recording technique was employed to investigate the mechanism conferring ATP sensitivity to a metabolite-sensitive K channel in insulin-secreting cells. ATP stimulated channel activity in the 0-10 microM range, but depressed it at higher concentrations. In inside-out patches, addition of the cAMP-dependent protein kinase inhibitor (PKI) reduced channel activity, suggesting that the stimulatory effect of ATP occurs via cAMP-dependent protein kinase-mediated phosphorylation. Raising ATP between 10 and 500 microM in the presence of exogenous PKI progressively reduced the channel activity; it is proposed that this inactivation results from a reduction in kinase activity owing to an ATP-dependent binding of PKI or a protein with similar inhibitory properties to the kinase. A model describing the effects of ATP was developed, incorporating these two separate roles for the nucleotide. Assuming that the efficacy of ATP in controlling the channel activity depends upon the relative concentrations of inhibitor and catalytic subunit associated with the membrane, our model predicts that the channel sensitivity to ATP will vary when the ratio of these two modulators is altered. Based upon this, it is shown that the apparent discrepancy existing between the sensitivity of the channel to low ATP concentrations in the excised patch and the elevated intracellular level of ATP may be explained by postulating a change in the inhibitor/kinase ratio from 1:1 to 3:2 owing to the loss of protein kinase after patch excision. At a low concentration of ATP (10-20 microM), a nonhydrolyzable ATP analogue, AMP-PNP, enhanced the channel activity when present below 10 microM, whereas the analogue blocked the channel activity at higher concentrations. It is postulated that AMP-PNP inhibits the formation of the kinase-inhibitor complex in the former case, and prevents phosphate transfer in the latter. A similar mechanism would explain the interaction between ATP and ADP which is characterized by enhanced activity at low ADP concentrations and blocking at higher concentrations.

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Myotubes from transgenic mdx mice expressing full-length dystrophin show normal calcium regulation.

Molecular Biology of the Cell ◽

10.1091/mbc.5.10.1159 ◽

1994 ◽

Vol 5 (10) ◽

pp. 1159-1167 ◽

Cited By ~ 17

Author(s):

W F Denetclaw ◽

F W Hopf ◽

G A Cox ◽

J S Chamberlain ◽

R A Steinhardt

Keyword(s):

Single Channel ◽

Calcium Regulation ◽

Full Length ◽

Mdx Mice ◽

Free Calcium ◽

Muscle Degeneration ◽

Channel Activity ◽

Mouse Muscle ◽

Calcium Dependent ◽

Normal Calcium

A lack of dystrophin results in muscle degeneration in Duchenne muscular dystrophy. Dystrophin-deficient human and mouse muscle cells have higher resting levels of intracellular free calcium ([Ca2+]i) and show a related increase in single-channel open probabilities of calcium leak channels. Elevated [Ca2+]i results in high levels of calcium-dependent proteolysis, which in turn increases calcium leak channel activity. This process could initiate muscle degeneration by further increasing [Ca2+]i and proteolysis in a positive feedback loop. Here, we tested the direct effect of restoration of dystrophin on [Ca2+]i and channel activity in primary myotubes from mdx mice made transgenic for full-length dystrophin. Transgenic mdx mice have been previously shown to have normal dystrophin localization and no muscle degeneration. Fura-2 calcium measurements and single-channel patch recordings showed that resting [Ca2+]i levels and open probabilities of calcium leak channels of transgenic mdx myotubes were similar to normal levels and significantly lower than mdx littermate controls (mdx) that lack dystrophin. Thus, restoration of normal calcium regulation in transgenic mdx mice may underlie the resulting absence of degeneration.

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