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息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Ｍａｒｋｏｖｘ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Ｍａｒｋｏ     

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.     

细胞膜离子单通道信号的统计重构算法研究

离子单通道信号是皮安级的随机离子流，用膜片钳技术可以记录下来，但由于信号的微弱性，记录中通道信号往往被背景噪声所淹没，传统上用阈值检测器消除噪声并重构信号，但信噪比低时，阈值检测器失效，本文提出了基于最大后验概率的状态估计和最大似然函数的序列估计两种信号的统计重构技术，在白色背景噪声和有色背景噪声情况下，分别进行仿真实验，证实其重构精度较高，鲁棒性较强，性能远比阈值检测器优越。     

滤波和有色背景噪声影响下细胞膜离子单通道信号的自适应恢复算法研究

为了克服反混叠滤波器和有色背景噪声的影响。本文提出了一种自适应算法，估计离子通道的动力学特征参数和背景噪声的统计特征。然后基于这些参数，运用统计技术从强噪声的膜片钳记录中恢复离子通道信号，这种算法叉耦合了递归的expectation-maximization(EM)算法和递归扩展最小二乘算法，递归EM算法最优地估计隐Markov模型参数，递归扩展最小二乘算法最优地估计背景噪声的特征。仿真研究表明这种交叉耦合算法一致收敛，并且对构象状态数目误差有很强的鲁棒性。     

大鼠背根神经节分离神经元的延时整流的钾离子单通道

运用膜片钳技术对急性分离的大鼠背根神经节神经元细胞上的电压依赖性钾离子通道进行了研究.在细胞贴附式记录模式下,去极化可以激活一个电导为20pS的钾离子单通道电流,分析了其单通道的特性,提出了其动力学的模型.对于了解大鼠背根神经节神经元细胞的电活动机制具有重要的意义.     

基于EM算法的自适应离子单通道信号参数估计技术研究

许多离子通道的电流信号特别微弱,运用标准的阈值检测器方法不能估计出通道信号的各种参数。基于隐Markov模型（HMM)的各种算法运算量大,不具有自适应功能。本文借用增广最小二乘法（ELS）参数辩识算法中的运算技巧,应用随机逼近原理,在EM算法的基础上推导出一种具有自适应能力的离子通道信号参数估计技术,仿真证明其估计精度较高,稳健性强,而且易于实现。     

在inside-out膜片上caffeine对猪冠状动脉平滑肌细胞钙激活钾通道的调节作用及ryanodine的影响

目的:利用膜片钳技术,研究咖啡因对钙激活钾通道(calcium-activated potassium channel,KCa)的作用机制,及咖啡因存在时兰尼定(ryanodine)对KCa的影响以阐明冠状动脉平滑肌的调控机制。方法:采用急性酶分离方法,应用膜片钳单通道电流记录技术记录猪冠状动脉平滑肌钿胞上KCa电流活动。电流信号经放大、滤波及A/D、D/A转换后输入微机进行采样和储存。应用PCLAMP9.0软件系统进行数据采集及分析。结果:在内面向外式(inside-out)膜片下,咖啡因(0.1、0.5、1.0、5.0mmol/L)可浓度依赖性地增加通道开放概率,而对电流幅值无明显影响,开放概率增加是通过明显缩短平均关闭时间实现的(n=8,P0.01);洗去药物后通道活性可以恢复到对照水平;5.0mmol/L咖啡因对KCa激活作用最大(P0.01)。在细胞贴附式(cell-attached)膜片上,咖啡因激活KCa后,ryanodine(10-40μmol/L)浓度依赖性地抑制通道开放概率,开放时间缩短,关闭时间延长,对电流幅度无明显影响。结论:在inside-out膜片下,咖啡因能够直接激活猪冠状动脉平滑肌细胞KCa通道。在cell-atta-ched构型上,ryanodine可通过胞内一定的信号通路浓度依赖性间接抑制咖啡因对KCa激活。     

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。     

Cell-attached膜片上,咖啡因对猪冠状动脉平滑肌细胞KCa的调节作用

目的:研究咖啡因对猪冠状动脉平滑肌细胞KCa通道的调控机理,以期揭示胞内钙库RyR激活后,局部钙离子浓度升高和KCa的关系。方法:采用急性酶分离方法,应用膜片钳单通道电流记录技术记录大脑皮层神经元猪冠状动脉平滑肌细胞上KCa通道电流活动。电流信号经放大、滤波及A/D、D/A转换后输入微机进行采样和储存。实验数据应用CLAMP9.0软件系统进行数据采集及分析。结果:在cell-attached膜片上咖啡因对KCa通道有明显的作用,咖啡(0.1-5.0 mM)可以增加通道的开放概率(NPo),呈现出浓度依赖性,开放时间延长,关闭时间也随之缩短,而对电流幅值无明显影响,开放概率的增加是通过明显缩短平均关闭时间实现的(n=8,P<0.05);洗去药物后通道活性可以一定程度的恢复到对照水平,再加入一定浓度咖啡因(如1.0mM)可再次激活KCa,激活程度与洗脱前较接近。结论:在细胞贴附式构型上咖啡因浓度依赖性地激活KCa,有饱和性。可能是通过影响胞内信号转导过程而调控KCa活性。     

A method for exceptionally low noise single channel recordings

Summary We present a method whereby, with integrating electronics, quartz patch electrodes and a novel use of silicone oil, background noise levels as low as .083 pA RMS in a 5 kHz bandwidth (4-pole Butterworth filter) have been achieved in single channel patch clamp recordings. These approaches result in much higher signal to noise ratios for single channel recording than have previously been reported and should allow many investigators to significantly reduce noise at a constant bandwidth or to increase their recording bandwidths by several kHz.     

伤口巨噬细胞离子通道活动的实验研究

目的：研究伤口巨噬细胞离子通道活动的特点。方法：采用cell-attached膜片离子单通道记录方法。结果：伤口巨噬细胞膜上可记录到离子通道自发开放，这些自发性开放的通道包括以钾离子为载体的阳离子通道与以氯离子为载体的阴离子通道。文中对伤口巨噬细胞离子通道的生理功能进行了初步探讨。     

Electrophysiologically identified subpopulations of taste bud cells

The heterogeneous population of mammalian taste cells includes several cellular subtypes specializing in distinct physiological functions. They are poorly understood at the single cell level because the available physiological data have generally been obtained from unidentified taste cells. We recorded them from individual taste cells isolated from circumvallate, foliate, and fungiform papilla of the mouse, employing the patch clamp technique, and tried to elucidate whether universal electrophysiological criteria may be established for the identification of functionally different cellular subpopulations. It was found that irrespective of the papillae type, most ( approximately 96%) of robust taste cells could be categorized into three distinct subgroups on the basis of families of whole-cell (WC) currents exhibited in response to membrane polarization. The validity of this quite simple criterion was further confirmed by using different voltage clamp protocols, ion substitutions, and channel blockers to record different ionic currents, including voltage-gated (VG) Ca(2+), inward-rectifying K(+), and hyperpolarization-activated currents. Given that our findings are based on the statistically significant number of recordings, we believe that the electrophysiological identification of taste cells presented here may be effective for further studies on single taste cell physiology, including taste transduction.     

The fractal random telegraph signal: Signal analysis and applications

A random telegraph signal is a time series whose value S(t) at time t is either one of only two possible values. Many processes including chemical reactions, cell membrane ion channels, and electronic noise generate such signals. Usually, Markov models have been used to model and analyze such data. Instead, we present a new fractal random telegraph signal that is statistically self-similar in time. We show how to analyze such signals and apply those techniques to study burst noise in a defective operational amplifier and ion currents recorded through individual ion channels in a cell membrane.     

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     

A thin slice preparation for patch clamp recordings from neurones of the mammalian central nervous system

(1) A preparation is described which allows patch clamp recordings to be made on mammalian central nervous system (CNS) neurones in situ. (2) A vibrating tissue slicer was used to cut thin slices in which individual neurones could be identified visually. Localized cleaning of cell somata with physiological saline freed the cell membrane, allowing the formation of a high resistance seal between the membrane and the patch pipette. (3) The various configurations of the patch clamp technique were used to demonstrate recording of membrane potential, whole cell currents and single channel currents from neurones and isolated patches. (4) The patch clamp technique was used to record from neurones filled with fluorescent dyes. Staining was achieved by filling cells during recording or by previous retrograde labelling. (5) Thin slice cleaning and patch clamp techniques were shown to be applicable to the spinal cord and almost any brain region and to various species. These techniques are also applicable to animals of a wide variety of postnatal ages, from newborn to adult.