Electrical characteristics of the ionic psn-junction as a model of the resting axon membrane

Summary As a model for the resting axon membrane, we propose the ionic psn-junction. Its electrical characteristics can be determined in close analogy to the corresponding electronic semiconductor junction. Using the semianalytic approximation, we calculated the electrical capacity and the ionic currents. In contrast to the abrupt pn-junction, the electrical capacity of the psn-junction turns out to be practically voltage-independent, as it is observed for the squid axon membrane. The passive ionic fluxes for K⁺, Na⁺ and Cl^–, as the main contributions to the total charge flux, are calculated and compared with literature data on the ion fluxes through the resting squid axon membrane as measured by use of radioactive tracers. From this comparison, the ionic permeabilities can be evaluated and used to compute the resting membrane conductivity, which is found to be close to the experimental value. Further evidence in favor of the proposed asymmetrical membrane structure and possible ways of its test by the methods of protein chemistry are discussed.Part of this work was carried out at the Institut für Physiologische Chemie, Universität München, during the tenure of a Habilitandenstipendium of the Deutsche Forschungsgemeinschaft.     

Fluctuations of the electrical characteristics of a membrane in stress states

The general scheme of calculation of current and voltage fluctuations obtained in [4] was applied to the definite theoretical membrane model based on the experimental data. Spectra for the extreme conditions of current and voltage fixation were obtained. The estimation of some parameters of the theory was carried out.     

Clustering of resting state networks

Background

The goal of the study was to demonstrate a hierarchical structure of resting state activity in the healthy brain using a data-driven clustering algorithm.

Methodology/Principal Findings

The fuzzy-c-means clustering algorithm was applied to resting state fMRI data in cortical and subcortical gray matter from two groups acquired separately, one of 17 healthy individuals and the second of 21 healthy individuals. Different numbers of clusters and different starting conditions were used. A cluster dispersion measure determined the optimal numbers of clusters. An inner product metric provided a measure of similarity between different clusters. The two cluster result found the task-negative and task-positive systems. The cluster dispersion measure was minimized with seven and eleven clusters. Each of the clusters in the seven and eleven cluster result was associated with either the task-negative or task-positive system. Applying the algorithm to find seven clusters recovered previously described resting state networks, including the default mode network, frontoparietal control network, ventral and dorsal attention networks, somatomotor, visual, and language networks. The language and ventral attention networks had significant subcortical involvement. This parcellation was consistently found in a large majority of algorithm runs under different conditions and was robust to different methods of initialization.

Conclusions/Significance

The clustering of resting state activity using different optimal numbers of clusters identified resting state networks comparable to previously obtained results. This work reinforces the observation that resting state networks are hierarchically organized.     

Generation of resting membrane potential

This brief review is intended to serve as a refresher on the ideas associated with teaching students the physiological basis of the resting membrane potential. The presentation is targeted toward first-year medical students, first-year graduate students, or senior undergraduates. The emphasis is on general concepts associated with generation of the electrical potential difference that exists across the plasma membrane of every animal cell. The intention is to provide students a general view of the quantitative relationship that exists between 1) transmembrane gradients for K(+) and Na(+) and 2) the relative channel-mediated permeability of the membrane to these ions.     

细胞静息膜电位的测量

实验表明,大细胞表面积与体积的比率是相当大的,以至于离子梯度的下降是极为缓慢的。即使代谢类毒物阻断了依赖ATP的能量代谢,静息膜电位也能维持相当长的时间,这表明依赖ATP的泵不是维持膜电位的直接能源。例如,应用地高辛(cardiac glycol— side)来抑制枪鸟贼巨轴突膜上的Na—K泵,细胞膜电     

Cation selectivity of the resting membrane of squid axon

Summary Permeability constant ratios among monovalent cations were studied in the resting membrane of a giant axon of a Pacific squid,Loligo opalescens, by observing the relationship between the membrane potential and the ion concentration.The average permeability ratios are: Tl, 1.8; K, 1.0; Rb, 0.72; Cs, 0.16; Na, <0.08; Li, <0.08. These permeability ratios suggest that neither valinomycin nor nonactin are adequate models for the sites producing the resting permeability in the axonal membrane.Cyclic polyetherbis(t-butyl cyclohexyl) 18-crown-6 does not increase the permeability ratioP _Cs/P _K except when applied at concentrations (5×10^–5 m) at which the surfactant properties of this molecule may become significant.     

Robust reproducible resting state networks in the awake rodent brain

Resting state networks (RSNs) have been studied extensively with functional MRI in humans in health and disease to reflect brain function in the un-stimulated state as well as reveal how the brain is altered with disease. Rodent models of disease have been used comprehensively to understand the biology of the disease as well as in the development of new therapies. RSN reported studies in rodents, however, are few, and most studies are performed with anesthetized rodents that might alter networks and differ from their non-anesthetized state. Acquiring RSN data in the awake rodent avoids the issues of anesthesia effects on brain function. Using high field fMRI we determined RSNs in awake rats using an independent component analysis (ICA) approach, however, ICA analysis can produce a large number of components, some with biological relevance (networks). We further have applied a novel method to determine networks that are robust and reproducible among all the components found with ICA. This analysis indicates that 7 networks are robust and reproducible in the rat and their putative role is discussed.     

细胞静息膜电位的产生和维持

根据中学生物学教学及教材中涉及到有关细胞膜电位的内容,特别请我刊编委、北京师范大学生命科学学院左明雪教授撰写了相关知识,将在2006年4、5、6期连续刊登。     

Spectral-correlation characteristics of the electrical activity of the brain of the rabbit in a state of calm wakefulness

Inter- and intrahemispheric relations of electrical activity of the pre-motor, sensorimotor (representation of forelimb and blinking) and visual zones of rabbit's cerebral cortex in calm alertness was studied by method of spectral-correlative analysis. Mean coherence levels of the EEG of tested hemispheric symmetric points and symmetric pairs of leads in the left and right hemispheres were characterized by a high temporal stability in the state of calm alertness and during sensory stimulation. A comparison of mean coherence values of EEG in symmetric leads, revealed a tendency to left-side dominance of statistical bonds of electrical processes. A tendency was shown towards interhemispheric asymmetry by mean parameters of EEG power spectra: the left hemisphere of the rabbit is characterized by a lower mean frequency of electrical activity and a more narrow effective frequency of the spectrum.     

The molecular organizational characteristics of the cell nucleus components at different phases of the mitotic cycle and in the resting state]

Data about the changes of the cell nucleus structure at different levels of its organization are summarized in the review. The data about the change of the DNA break number during the cycle and in resting state are presented and the role of the changes of the repair efficiency in this process is discussed. The changes of the chromatin protein spectrum, the chromatin structure at nucleosomal and supranucleosomal levels, the DNA superhelicity, topoisomerase activity, nuclear matrix composition and structure are discussed as well. The nucleus structure during the S-phase and mitosis and the cycle-related changes of the chromatin structure in lower eukaryotes are reviewed separately.