基于小波变换的离子单通道信号的分析方法

在单通道信号处理中引入尺度能量分布的概念，利用小波变换，通过提取具有特征频率的高频信号，可以在不失真的条件下将单通道信号清晰地检测出来，消除噪声干扰。本文提供的方法在离子通道信号处理中具有较普遍的意义。     

低信噪比离子通道信号的噪声统计消除技术

细胞膜离子单通道信号是一种状态有限、一阶齐次的Markov过程，并且膜片钳记录中以较低频率采样时，由于混叠效应可以认为背景噪声是高斯白噪声^[1]。基于这两个前提我们应用隐式马尔科夫模型（Hidden Markov Model,HMM)信号处理技术来消除膜片钳记录时微弱单通道信号的背景噪声。通过仿真证实该技术可高精度地去除膜片钳记录中白色高斯噪声对微弱单通道信号的干扰。     

基于随机松弛的离散HMM参数估计和信号恢复

细胞膜离子单通道信号是皮安级的跨膜随机离子电流,由于信号的微弱性,膜片钳技术记录中单通道电流往往淹没在强背景噪声中.传统上采用阈值检测器来恢复通道电流信号,这需要人为设定阈值,尤其是信噪比低时,阈值检测器失效.本研究采用隐马尔可夫模型（HMM）的通道信号恢复及参数估计技术,首先利用基于随机松弛（SR）的离散HMM参数全局优化算法,估计通道的动力学参数,确保模型训练中参数收敛到全局最优.在此基础上,从噪声污染的膜片钳记录中恢复通道电流信号.理论和实验结果表明,在低信噪比情况下（SNR＜5.0）,该方法用于白噪声背景下细胞膜离子单通道参数估计和信号恢复时,参数收敛速度快,信号恢复精度高,算法抗噪能力强,可以较好地描述实际对象特性.     

基于自相关约束的信号波形估计及其在诱发电位提取中的应用

从观测数据中估计源信号的波形一直是信号处理领域中的一个重要问题.利用源信号的时间自相关函数构造一个非线性方程组,借助大规模数值计算方法,把原来直接估计源信号这样一个较困难的问题,转化为估计迭代初始值与源信号时间自相关函数的问题.使用小波模极大值法,估计迭代初始值与源信号时间自相关函数,再对方程组迭代求解,收敛后的结果即为对源信号的估计.将该方法应用于诱发电位的单通道、单次提取实验,在信噪比为0 dB时,提取结果与源信号的相关系数约为0.93,对幅度与潜伏期的估计都比较准确.实验结果表明,算法性能受迭代初始值估计精度与源信号时间自相关函数估计精度的影响,受前者影响较小,而受后者的影响相对较大.     

基于单通道FVEP提取的虚拟式颅内压无创检测仪器的实现

研究单通道FVEP信号提取的综合分析方法及其应用。考虑单通道FVEP信号提取的特殊性,引入了参考源通道以满足独立分量分析的应用条件,从而实现单通道FVEP信号与背景EEG噪声的分离;考虑参考源通道与实际检测中的背景噪声不完全匹配而可能带来的消噪效果不理想的问题,利用叠加平均技术与叠加次数的平方根成正比的特性,通过少次的叠加来进一步提高单通道FVEP信号的信噪比;最后利用多分辨率小波变换的多分辨率特性,实现FVEP信号的有效提取。此方法用于虚拟式颅内压无创检测分析仪的临床实验证明了本方法在实现颅内压无创检测方面的有效性。     

基于扩展卡尔曼滤波和奇异值分解算法的单通道胎儿心电提取方法

提出一种将扩展卡尔曼滤波(EKF)算法和奇异值分解(SVD)算法相结合的单通道胎儿心电提取方法。首先,建立母体心电的动态模型,利用该模型通过扩展卡尔曼滤波或扩展卡尔曼平滑(EKS),从孕妇的单通道腹部信号中估计出母体心电成分,然后与单通道腹部信号相减得到胎儿心电信号的初步估计,随后再利用奇异值分解算法,对初步估计出的胎儿心电信号进行去噪处理,以期得到高信噪比的胎儿心电信号。另外,针对胎儿心律不齐的情况,在奇异值分解算法中提出一种改进的心电信号重构矩阵构造方法。对合成腹部信号和实际腹部信号(源于DaISy数据库和PhysioNet中的非侵入式胎儿心电数据库,共计49个腹部通道的数据),进行胎儿心电提取实验。结果表明,使用EKF+SVD或EKS+SVD的算法比单独使用EKF或EKS的算法,提取出的胎儿心电信号的信噪比提高约5 dB,胎儿心电提取的准确性分别达95.60%和95.94%。结合EKF和SVD算法的单通道胎儿心电提取方法,可以有效地提高胎儿心电信号的信噪比和提取的准确性,并且适用于母体或胎儿心律不齐的情况。     

利用运动单位发放信息建立多通道信息的表面肌电信号分解

目的基于多通道信息的表面肌电(surfaceelectromyographic,sEMG)信号分解有助于弥补单通道分解时空间和发放信息不足的缺点.本文提出利用运动单位(motorunit,MU)的发放信息建立多通道 sEMG信号中属于同一 MU的模板映射关系,实现多导信号的信息互补,从而提高分解的准确率.方法对四导仿真信号先分别进行单通道分解,然后利用各通道之间的发放信息建立模板映射关系进行多通道分解.结果仿真实验结果显示单通道分解准确率平均为75%,多通道分解准确率为88%,表明利用MU发放信息建立模板映射关系进行sEMG信号分解能够提高分解有效性.结论将该方法应用于真实信号分解,也能有效得到 MU的波形和发放信息.     

基于HMM的低信噪比离子通道信号的恢复及参数估计

细胞膜离子单通道信号是皮安级的随机电流 ,膜片钳技术可以记录这些信号。一般认为它是一阶的、状态有限的 Markov过程。某些种类的离子通道 ,电流信号特别微弱 ,完全淹没在背景噪声中 ,传统的膜片钳技术很难检测到 ,只能运用数学方法恢复和估计。在低采样频率情况下 ,由于混叠效应 ,可认为背景噪声是白色的 ;在高采样频率条件下 (高于奈奎斯特频率 ) ,背景噪声是有色的。本文分别综述了白色背景噪声条件下基于隐式 Markov模型和有色背景噪声条件下基于隐式矢量 Markov模型的低信噪比离子单通道信号的恢复和参数估计 ,主要包括前后向算法、EM算法等     

细胞膜离子单通道信号的频域分析方法

利用离散小波变换构造尺度能量分布函数 (Power distribution function,PDF) ,分析单通道信号的频域特征 ;同时采用功率密度谱 (Power spectral density,PSD)方法进行分析。结果表明 ,基于离散小波变换 (Discretewavelet transform,DWT)的尺度能量分布是一种非常有效的单通道信号的频域分析方法。     

一种用于超声多普勒回波信号解调的单通道乘法器电路

为准确、快速提取超声多普勒频移信号,本研究提出了一种结构简单、成本低廉的单通道乘法器电路.该电路的一路输入为超声回波信号,另一路为与发射信号频率有确定频差的正弦波.通过设计的多普勒信号模拟装置对电路进行测试,并对实验数据进行频谱分析,结果显示,解调得到的多普勒频移信号的频率符合多普勒效应的原理.实验证明,本研究的单通道...     

A novel method for analysis of single ion channel signal based on wavelet transform

A single ion channel signal was analysed by the power distribution fraction constructed by a discrete wavelet transform. Average opening time and energy distribution of the signal can be obtained directly by this method. The method can also be used when the signal is corrupted by noise. By contrast, the conventional frequency domain analysis method--power spectral density--is less effective. Power distribution fraction will therefore give more useful information in analysis of experimental ion channel signals, principally by giving values of the mean channel opening time. The method may be applied to distinguish different ion channels more efficiently and to find their reactions to drugs.     

A patch-clamp analysis of membrane currents in salamander olfactory receptor cells

Isolated olfactory receptor cells were obtained from salamander olfactory epithelium and kept in short term culture conditions. They were studied by means of the whole cell patch-clamp technique associated with ionic substitutions and channel blockers. Under physiological ionic gradients, these cells had a resting potential of –39±10 mV and an input resistance above 2 G.Using different channel blockers and ion substitutions, we could separate several distinct components in the overall whole cell current. In most cells, inward current reflected the activation of a TTX resistant conductance which was blocked by cobalt ions. This inward current lasted only for about 5 min of whole cell recording. In a minority of cells, a TTX sensitive sodium current was also observed.The outward K⁺ current was blocked when the cells were loaded with cesium and tetraethylammonium. It inactivated slowly and incompletely and could act as a depolarization limiter in case of intense odour stimulations. Single channel analysis from outside out patches suggested that it corresponded to the activity of 34 pS channels. In some cells a rapidly inactivating K⁺ current was also present.Single channel activities (27±6 pS) were commonly recorded with KCl-filled pipettes, at resting or hyperpolarized membrane potentials but not at depolarized potentials. Membrane hyperpolarization increased the open-state probability. A preliminary study with odorant stimulations indicated the existence of a stimulus-induced current probably corresponding to the activation of the chemoreceptive membrane.     

Single Ca-activated cation channels in bursting neurons ofHelix

The depolarizing drive that maintains bursting inHelix neurons is carried by a long-lasting calcium-activated inward current. This current was studied using cell-attached and inside-out patches from the right parietal fast burster neuron ofHelix pomatia.One population of unitary currents was inward at –50 mV and showed an increased probability of opening when Ca²⁺ was injected or when excised patches were bathed in solutions with 10^–7 to 10^–5 M free Ca²⁺ levels. Cell-attached patches (patch electrodes filled with 10^–7 M Ca²⁺ Ringer) had single channel conductances near 30 pS with reversal potentials near –20 mV; excised patches had similar conductances in symmetrical Na⁺ solutions and reversal potentials within a few millivolts of zero. Calculations, assuming a simple spherical cell, yield a channel density of only about 1/6 m². The increased channel opening probability characteristically persisted well beyond the duration of transient whole-cell inward current. We conclude from this that the later phase of Ca-activated inward currents is normally masked by outward currents.     

The automated analysis of data from single ionic channels

The development of single channel recordings has brought with it the need to analyse enormous amounts of data. The data analysis is time consuming and subject to observer biases since the events are random in time and are contaminated with uncorrelated noise. We have developed a heuristic pattern recognition program which identifies with high precision single channel currents and rejects contaminating noise. The program interactively provides for a variety of amplitude and duration measures. Analysis is flexible and rapid: a file containing over 10,000 events can be analysed in under 2 h.Specific detection features include variable lowpass filtering, automatic baseline restoration, and adaptive amplitude thresholds. A record is analysed through duration histograms, binomial estimates of the number of active channels present, cross-correlation estimates between parameters, spectral analysis of events and background noise, and stationarity of mean channel current. The graphic output facilities can plot raw data (after filtering and baseline restoration) with the idealized signal superimposed or with detected events underlined. A batch processing facility has been included to allow processing of data during periods of low computer demand.     

Electrical events during gamete maturation and fertilization in animals and humans

Gamete cells are electrogenic, i.e. capable of responding to electrical stimuli and modifying their electrical properties during the crucial periods of maturation and fertilization. Ion channels have been widely demonstrated on the plasma membrane of the oocyte and spermatozoon in all animals studied, and electrical modifications in gametes are due to ion currents that are modulated via these ion channels. The modification of intracellular calcium levels in gametes has been extensively studied, and these modifications are recognized to be a second messenger system for gamete maturation and fertilization. Other ions also move through the plasma membrane, either in association with or independent of calcium, and these generate typical features such as fertilization currents and oscillation of resting potential. These modifications were first studied in marine invertebrates, and the observations subsequently compared with mammalian systems, including human. The precise role played by these currents in the processes of maturation and fertilization is still poorly understood; however, recent research opens new frontiers for their clinical and technological application.     

A newly identified Ca2+ dependent K+ channel in the smooth muscle membrane of single cells dispersed from the rabbit portal vein

We found a new type of Ca²⁺-dependent K⁺ channel in smooth muscle cell membranes of single cells of the rabbit portal vein. A slope conductance of the current was 180 pS when 142 mM K⁺ solution was exposed to both sides of the membrane (this channel was named the K_M channel, in comparison to the known K_L and K_S channels from the same membrane patch; Inoue et al. 1985). This K_M channel was less sensitive to the cytoplasmic Ca²⁺ concentration, [Ca²⁺]_i, but was sensitive to the extracellular Ca²⁺, [Ca²⁺]_o, e.g. in the outside-out membrane patch, lowering the [Ca²⁺]_o in the bath markedly reduced the open probability of this channel, and also in cell-attached configuration, lowering of the [Ca²⁺]_o using the internally perfused patch clamp electrode device reduced the opening of K_M channel. TEA⁺ (1–10 mM) reduced the amplitude of the elementary current through the K_M channel applied from each side of the membrane, but this agent inhibited the K_M channel to a greater extent when applied to the inner than to the outer surface of the membrane. Furthermore, this K_M channel had a weak voltage dependency, and the open probability of the channel remained much the same within a wide range of potential (from –60 mV to +60 mV). Whereas most Ca²⁺-dependent K⁺ channels are regulated mainly by [Ca²⁺]_i and possess a voltage dependency, these properties of the K_M channel differed from other Ca²⁺-dependent K⁺ channels. The elucidation of this K_M channel should facilitate explanations of the actions of external Ca²⁺ or TEA⁺ on the membrane potential, in the smooth muscles of the rabbit portal vein.     

Single channel activity associated with the calcium dependent outward current inHelix pomatia

A recently improved version of the extracellular patch clamp technique (9, 13) was used to record currents from microscopic membrane areas of Helix neurons with predominant Ca²⁺ dependent outward currents. Current fluctuations in the patches consisted mainly of frequently interrupted, one-sided steps indicating discrete open-closed state changes of single channels with an ohmic conductance of approximately 19 pS. Frequency of occurrence of the elementary events compares with amplitudes of macroscopic currents during depolarizing voltage steps of varied amplitude. Average delays in appearance of the events vary in line with delayed time courses of the cell's outward current.     

荧光共振能量转移技术在细胞离子研究中的应用

细胞许多新陈代谢活动都伴随着离子浓度的改变,通过对离子浓度的检测可以间接检测细胞代谢状态。荧光共振能量转移技术(fluorescence resonance energy transfer,FRET)可以实现在活细胞内对离子浓度微弱变化的动态检测,为细胞离子代谢的可视化检测提供了有力工具。本文综述了FRET技术在离子浓度、离子通道以及膜电位检测方面的应用。