scholarly journals Origins of open-channel noise in the large potassium channel of sarcoplasmic reticulum.

1994 ◽  
Vol 104 (5) ◽  
pp. 857-883 ◽  
Author(s):  
A H Hainsworth ◽  
R A Levis ◽  
R S Eisenberg
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Open Channel ◽  
Single Channel ◽  
Channel Noise ◽  
Mean Power ◽  
Channel Current ◽  
Power Spectral ◽  
The Mean ◽  
Aqueous Species

Open-channel noise was studied in the large potassium channel of the sarcoplasmic reticulum (SR). Inside-out patches were excised directly from the SR of split skeletal muscle fibers of lobster, with lobster relaxing ringer (LRR) in bath and pipette. The power spectrum of open-channel noise is very low and approximately flat in the 100 Hz-10 kHz frequency range. At 20 degrees C, with an applied voltage of 50 mV, the mean single-channel current (i) is 9 pA (mean single-channel conductance = 180 pS) and the mean power spectral density 1.1 x 10(-29) A2/Hz. The latter increases nonlinearly with (i), showing a progressively steeper dependence as (i) increases. At 20 mV, the mean power spectral density is almost independent of (i) and approximately 1.4 times that of the Johnson noise calculated for the equivalent ideal resistor with zero net current; at 70 mV it increases approximately in proportion to (i)2. The mean power spectral density has a weak temperature dependence, very similar to that of (i), and both are well described by a Q10 of 1.3 throughout the range 3-40 degrees C. Discrete ion transport events are thought to account for a significant fraction of the measured open-channel noise, probably approximately 30-50% at 50 mV. Brief interruptions of the single-channel current, due either to blockage of the open channel by an extrinsic aqueous species, or to intrinsic conformational changes in the channel molecule itself, were a possible additional source of open-channel noise. Experiments in modified bathing solutions indicate, however, that open-channel noise is not affected by any of the identified aqueous species present in LRR. In particular, magnesium ions, the species thought most likely to cause brief blockages, and calcium and hydrogen ions, have no detectable effect. This channel's openings exhibit many brief closings and substrates, due to intrinsic gating of the channel. Unresolved brief full closings are calculated to make a negligible contribution (< 1%) to the measured power spectral density. The only significant source of noise due to band width-limited missed events is brief, frequent 80% substrates (mean duration 20 microseconds, mean frequency 1,000 s-1) which account for a small part of the measured power spectral density (approximately 14%, at 50 mV, 20 degrees C). We conclude that a large fraction of the measured open-channel noise results from intrinsic conductance fluctuations, with a corner frequency higher than the resolution of our recordings, in the range 10(4)-10(7) Hz.(ABSTRACT TRUNCATED AT 400 WORDS)

Feedback regulation of Na channels in rat CCT. III. Response to cAMP

1995 ◽  
Vol 268 (3) ◽  
pp. F480-F489 ◽  
Author(s):  
G. Frindt ◽  
R. B. Silver ◽  
E. E. Windhager ◽  
L. G. Palmer
Keyword(s):  
Open Channel ◽  
Single Channel ◽  
Feedback Inhibition ◽  
Feedback Regulation ◽  
Na Channels ◽  
Patch Clamp Technique ◽  
Channel Current ◽  
Fluorescence Measurements ◽  
Collecting Tubule ◽  
The Mean

The effects of exogenous adenosine 3',5'-cyclic monophosphate (cAMP) on apical Na channels in the rat cortical collecting tubule were studied using the patch-clamp technique and fura 2 fluorescence measurements of intracellular Ca2+ (Ca2+i). When the permeant analogue, 8-(4-chlorophenylthio)-cAMP (CPT-cAMP, 200 microM), was added to the superfusate during recording from cell-attached patches, both the mean number of open channels (NPo) and the single-channel current (i) decreased within 3 min. When the superfusate also contained amiloride (10 microM), there was no effect of CPT-cAMP on either NPo or i. When CPT-cAMP was added to the bath before formation of the patch, the density of conducting channels was increased from 10 +/- 2 to 37 +/- 6 per patch, as estimated by analysis of channel-induced noise. This suggests that cAMP increases open-channel density in the regions of the apical membrane outside the patch but not within the patch. Channels already active in the patch before stimulation with the nucleotide are subject to feedback inhibition secondary to increased Na entry into the cell. CPT-cAMP increased Ca2+i from 104 to 198 nM. This increase in Ca2+i was abolished by benzamil (0.5 microM) or by low extracellular Ca2+. The cAMP-dependent reduction in NPo was still observed in Ca(2+)-free medium, indicating that a rise in Ca2+i was not essential for the feedback response. The decrease in NPo was attenuated, however, when cAMP was added in the absence of Ca2+ and in the presence of ouabain (1 mM) in the superfusate.(ABSTRACT TRUNCATED AT 250 WORDS)

Optimal Wiener Filter for a Body Mounted Inertial Attitude Sensor

2008 ◽  
Vol 61 (3) ◽  
pp. 455-472 ◽  
Author(s):  
Peter Rizun
Keyword(s):  
Spectral Density ◽  
White Noise ◽  
Power Spectral Density ◽  
Human Body ◽  
Linear Acceleration ◽  
Mean Square ◽  
White Noise Process ◽  
Noise Process ◽  
Power Spectral ◽  
The Mean

An optimal attitude estimator is presented for a human body-mounted inertial measurement unit employing orthogonal triads of gyroscopes, accelerometers and magnetometers. The estimator continuously fuses gyroscope and accelerometer measurements together in a manner that minimizes the mean square error in the estimate of the gravity vector, based on known spectral characteristics for the gyroscope noise and the linear acceleration of points on the human body. The gyroscope noise is modelled as a white noise process of power spectral density δn2/2 while the linear acceleration is modelled as the derivative of a band-limited white noise process of power spectral density δv2/2. The estimator is robust to centripetal acceleration and guaranteed to have zero mean error regardless of the motion of the sensor. The mean square angular error in attitude is shown to be independent of the module's angular velocity and equal to 21/2g−1/2δn3/2δv1/2.

scholarly journals Power Spectral Density Response of Bridge-Like Structures Loaded by Stochastic Moving Forces

2019 ◽  
Vol 2019 ◽  
pp. 1-10
Author(s):  
Silvio Sorrentino
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Spectral Density Function ◽  
Mean Value ◽  
Moving Loads ◽  
Mean Values ◽  
Power Spectral ◽  
Potential Applications ◽  
Spectral Density Functions ◽  
The Mean

In this study, simple and manageable closed form expressions are obtained for the mean value, the spectral density function, and the standard deviation of the deflection induced by stochastic moving loads on bridge-like structures. As a basic case, a simply supported beam is considered, loaded by a sequence of concentrated forces moving in the same direction, with random instants of arrival, constant random crossing speeds, and constant random amplitudes. The loads are described by three stochastic processes, representing an idealization of vehicular traffic on a bridge in case of negligible inertial coupling effects between moving masses and structure. System’s responses are analytically determined in terms of mean values and power spectral density functions, yielding standard deviations, with the possibility to easily extend the results to more refined models of single span bridge-like structures. Potential applications regard structural analysis, vibration control, and condition monitoring of traffic excited bridges.

Evolutionary power spectral density of strong-motion earthquakes

1970 ◽  
Vol 60 (3) ◽  
pp. 891-900 ◽  
Author(s):  
S. C. Liu
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Strong Motion ◽  
Earthquake Simulation ◽  
Power Spectral ◽  
Power Spectral Densities ◽  
Frequency Independent ◽  
Peak Location ◽  
The Mean ◽  
Earthquake Accelerograms

Abstract This paper presents the evolutionary (time-dependent) power spectral density curves of six strong-motion earthquakes. The earthquake accelerograms are treated as piecewise-separable and the frequency-independent modulating function is estimated by applying the mean square minimization criterion. The results show that, as the time increases, the power spectral densities of earthquakes can vary both in magnitude and in peak location over the frequency axis. The analysis demonstrates that the nonstationary characteristics of earthquakes can be reasonably assessed by a simple computation procedure and the information thus obtained can be helpful in developing improved stochastic models for earthquake simulation.

Spectral aspect of earthquakes

1959 ◽  
Vol 49 (1) ◽  
pp. 91-98
Author(s):  
William T. Thomson
Keyword(s):  
Spectral Density ◽  
Power Spectral Density ◽  
Statistical Approach ◽  
Wave Shape ◽  
Ground Acceleration ◽  
Power Spectral ◽  
The Mean ◽  
Energy Theory ◽  
Equipartition Of Energy ◽  
Wave Shapes

Abstract Considering ground acceleration associated with earthquakes to be composed of a series of velocity impulses of random amplitude, time spacing, and wave shapes, a statistical approach is used to establish its power spectral density. The general result indicates that if the mean of the velocity pulses is zero, the power spectral density becomes a constant, regardless of wave shape and time spacing, thereby supporting the equipartition of energy theory, first advanced by Housner.

Ion channel block by acetylcholine, carbachol and suberyldicholine at the frog neuromuscular junction

1985 ◽  
Vol 225 (1240) ◽  
pp. 329-355 ◽  
Keyword(s):  
Open Channel ◽  
Single Channel ◽  
Equilibrium Constants ◽  
Channel Noise ◽  
Muscle Fibres ◽  
Frog Neuromuscular Junction ◽  
Open Time ◽  
The Mean ◽  
Single Channel Currents ◽  
Channel Currents

Three nicotinic agonists, suberyldicholine, acetylcholine and carbachol, have been investigated by single channel recording at the endplates of adult frog muscle fibres. All three agonists can block the channels that they open. Suberyldicholine is the most potent blocker; it has an equilibrium constant for binding to the open channel of about 6 μM and blockages last for about 5 ms on average, at —105 mV. A plot of the mean number of blockages per unit open time against concentration (‘blockage frequency plot’) suggests that suberyldicholine does not produce long-lived blocked states such as might occur, for example, if it could be trapped within a shut channel. The characteristics of the 'blockage frequency plot’ are analysed in Appendix 2. Block by acetylcholine and carbachol has much lower affinity (the equilibrium constants being a few millimolar for both), and blockages are much briefer, so that blockage appears to produce noisy single channel currents of reduced amplitude. A method based on the spectral density of the excess ‘open’ channel noise has been used to investigate the rate of blocking and unblocking. The basis of this method is discussed in Appendix 1. It is estimated that the mean duration of a blockage is about 18 μs for acetylcholine and 9 μs for carbachol.

scholarly journals Ca2+ block and flickering both contribute to the negative slope of the IV curve in BK channels

2013 ◽  
Vol 141 (4) ◽  
pp. 499-505 ◽  
Author(s):  
Indra Schroeder ◽  
Gerhard Thiel ◽  
Ulf-Peter Hansen
Keyword(s):  
Open Channel ◽  
Single Channel ◽  
Bk Channels ◽  
Negative Slope ◽  
Channel Noise ◽  
Channel Current ◽  
Single Channel Current ◽  
Current Voltage ◽  
Per Se ◽  
Iv Curves

Single-channel current–voltage (IV) curves of human large-conductance, voltage- and Ca2+-activated K+ (BK) channels are quite linear in 150 mM KCl. In the presence of Ca2+ and/or Mg2+, they show a negative slope conductance at high positive potentials. This is generally explained by a Ca2+/Mg2+ block as by Geng et al. (2013. J. Gen. Physiol. http://dx.doi.org/10.1085/jgp.201210955) in this issue. Here, we basically support this finding but add a refinement: the analysis of the open-channel noise by means of β distributions reveals what would be found if measurements were done with an amplifier of sufficient temporal resolution (10 MHz), namely that the block by 2.5 mM Ca2+ and 2.5 mM Mg2+ per se would only cause a saturating curve up to +160 mV. Further bending down requires the involvement of a second process related to flickering in the microsecond range. This flickering is hardly affected by the presence or absence of Ca2+/Mg2+. In contrast to the experiments reported here, previous experiments in BK channels (Schroeder and Hansen. 2007. J. Gen. Physiol. http://dx.doi.org/10.1085/jgp.200709802) showed saturating IV curves already in the absence of Ca2+/Mg2+. The reason for this discrepancy could not be identified so far. However, the flickering component was very similar in the old and new experiments, regardless of the occurrence of noncanonical IV curves.

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