Open channel noise. VI. Analysis of amplitude histograms to determine rapid kinetic parameters

Heinemann, Stefan; Sigworth, Fred J.

doi:10.1016/s0006-3495(91)82087-2

Cited by 54 publications

(41 citation statements)

References 19 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In biological systems, shot noise and noise from conformational variations are now widely recognized as sources of fluctuations in open channel currents [7], In this study, we demonstrate that noise analysis can also be used to measure the rate constants of rapid chemical reactions that occur within the pore of a channel, if those reactions modulate the open channel conductance. We report that current noise may be produced by the reversible protonation of amino-acid sites in the channelforming molecule.…”

mentioning

confidence: 84%

See 1 more Smart Citation

Current noise reveals protonation kinetics and number of ionizable sites in an open protein ion channel

1993

View full text Add to dashboard Cite

In analogy to current fluctuations found in solid state electronic microstructure devices, excess noise generated by the reversible ionization of sites in a transmembrane ionic channel was observed. By analyzing the pH-dependent fluctuations in the current through fully open single channels formed by the a-toxin protein, we were able to evaluate the protonation rate constants, the number of sites participating in the protonation process, and the effect of recharging a single site on the channel conductance.PACS numbers: 87.22.Bt, 66.10.Ed, 82.30.Fi Ions in aqueous solution cannot cross the poorly polarizable lipid bilayer membranes surrounding cells [1]. Instead, they pass through ion channels formed by a class of membrane spanning proteins that play key roles in the generation of nerve action potentials, cell-cell communication, and other critical cellular functions [2]. Protein ion channels have multiple conformation states, some of which have a hydrophilic pore open to the flow of ions. The difference in energy between these states is sufficiently small that thermal fluctuations cause ion channels to switch between different levels of conductance. Transitions between states in a single molecule can therefore be observed as a fluctuating ion current [3] in analogy to recent observations of the light-scattering signal from a single trapped ion switching between different energy levels [4,5].Noise analysis has been successfully used to develop a molecular understanding of physical and chemical systems [6]. In biological systems, shot noise and noise from conformational variations are now widely recognized as sources of fluctuations in open channel currents [7], In this study, we demonstrate that noise analysis can also be used to measure the rate constants of rapid chemical reactions that occur within the pore of a channel, if those reactions modulate the open channel conductance. We report that current noise may be produced by the reversible protonation of amino-acid sites in the channelforming molecule. Moreover, we show that this technique can be used to determine the number of ionizable sites that modulate the channel conductance. The mechanism of the phenomenon we report here is analogous to that found for conductance fluctuations in solid state devices where recharging of a single trap [8,9] or a chain of localized states [10] was shown to be the fluctuation source.Current through the channel formed by the a-toxin protein [11] was measured with Ag-AgCl electrodes placed in compartments of a Teflon chamber illustrated in Fig. 1. The current recordings in Fig. 2 show the spontaneous formation of a single channel at three different pH values. Two features are clearly seen. First, the mean conductance of the a-toxin channel decreases when the p\\ is increased over the range 4.5

show abstract

mentioning

confidence: 84%

“…4 are caused by structural fluctuations. In this case, at least for linear models of noise generation, the spectral density of current noise should be proportional to the square of the mean channel current [7]. However, this is not true (Fig.…”

mentioning

confidence: 99%

Current noise reveals protonation kinetics and number of ionizable sites in an open protein ion channel

1993

View full text Add to dashboard Cite

show abstract

“…Detailed discussions of these can be found in textbooks on basic statistics, such as Spiegel (1975), Bevington (1969) and Kendall (1947) (see also Fesce, 1990;Heinemann and Sigworth, 1991). A short summary is given here.…”

Section: Appendix a Some Principles Of Statisticsmentioning

confidence: 99%

Combining deconvolution and fluctuation analysis to determine quantal parameters and release rates

Neher

Sakaba

2003

Journal of Neuroscience Methods

View full text Add to dashboard Cite

Analysis methods are described which integrate information from fluctuation analysis with that from deconvolution. Together the two approaches allow to derive a consistent quantitative description of quantal release (both evoked, spontaneous and asynchronous) under conditions in which quantal parameters may change during a repetitively applied stimulation protocol. Specifically, our methods take into account the effects of accumulating transmitter in the synaptic cleft and postsynaptic receptor desensitization, which may develop during strong stimulation. Several ways to handle non-stationarities are described. Examples are provided for the Calyx of Held, a glutamatergic synapse, in which both the pre- and the postsynaptic compartments can be voltage-clamped.

show abstract

“…2) are more the realm of biophysicists: whereas these fast processes may at first glance not be immediately relevant for physiological function, their analysis provides crucial clues to the understanding of stability and dynamics of ion channels and their interaction with blockers or other molecules. 24,25,32,33 Furthermore, computational approaches like molecular dynamics simulations are becoming increasingly powerful, and it is expected that they will be able to predict gating dynamics ( Fig. 1) based on the dynamics of individual chemical interactions or conformational changes in a protein.…”

Section: Introductionmentioning

confidence: 99%

“…33 Instead of a beta distribution they used the sum of gaussians and their higher-order cumulants to analyze the ca. 1 ms short closures of gramicidin channels recorded at 10 kHz bandwidth.…”

mentioning

confidence: 99%

How to resolve microsecond current fluctuations in single ion channels: The power of beta distributions

Schroeder

2015

Channels

View full text Add to dashboard Cite

A main ingredient for the understanding of structure/ function correlates of ion channels is the quantitative description of single-channel gating and conductance. However, a wealth of information provided from fast current fluctuations beyond the temporal resolution of the recording system is often ignored, even though it is close to the time window accessible to molecular dynamics simulations. This kind of current fluctuations provide a special technical challenge, because individual opening/closing or blocking/ unblocking events cannot be resolved, and the resulting averaging over undetected events decreases the singlechannel current. Here, I briefly summarize the history of fastcurrent fluctuation analysis and focus on the so-called "beta distributions." This tool exploits characteristics of current fluctuation-induced excess noise on the current amplitude histograms to reconstruct the true single-channel current and kinetic parameters. A guideline for the analysis and recent applications demonstrate that a construction of theoretical beta distributions by Markov Model simulations offers maximum flexibility as compared to analytical solutions.

show abstract

Open channel noise. VI. Analysis of amplitude histograms to determine rapid kinetic parameters

Cited by 54 publications

References 19 publications

Current noise reveals protonation kinetics and number of ionizable sites in an open protein ion channel

Current noise reveals protonation kinetics and number of ionizable sites in an open protein ion channel

Combining deconvolution and fluctuation analysis to determine quantal parameters and release rates

How to resolve microsecond current fluctuations in single ion channels: The power of beta distributions

Contact Info

Product

Resources

About