Electrical Properties Of Cells Research Articles

Synaptic responses and electrical properties of cells in brain slices of the mouse anteroventral cochlear nucleus

Intracellular recordings were made from cells in brain slices of the anteroventral cochlear nucleus. Responses to electrical stimulation of the stump of the auditory nerve were: (1) all-or-none, following the stimulus with no delay, and insensitive to the removal of extracellular Ca2+, probably representing the firing of directly stimulated auditory nerve fibers, or (2) graded, excitatory postsynaptic potentials, with synaptic delays of about 0.7 msec, which were often followed by graded, inhibitory synaptic potentials with synaptic delays of 1.2 msec or longer. The excitatory and inhibitory synaptic potentials were abolished by the removal of extracellular Ca2+. The result that delays of inhibitory synaptic responses were at least 2 times as long as those of excitatory ones indicates that probably an additional synapse was interposed. Responses to intracellularly injected current pulses show that cells in the anteroventral cochlear nucleus have one of two types of electrical characteristics. Type I properties are characterized by linear current-voltage relationships in the subthreshold voltage range and large, regularly firing action potentials in the suprathreshold range. Type II properties are characterized by nonlinear current-voltage relationships; suprathreshold depolarization elicits only one or two small action potentials. Type II characteristics are particularly well suited for maintaining the information contained in the timing and patterns of firing of the auditory nerve fibers.

The molecular basis of neurotransmission at the muscarinic receptor

Neurotransmitters, hormones, and many drugs cause their effects by interacting specifically with their receptors. In most cases these receptors are highly specialized proteins on the outside surface of the cell. For agonists but not antagonists these interactions may induce conformational changes in the receptor molecule. These receptor changes induced by agonists may affect the electrical properties of cells by changing the membrane permeability, which ultimately leads to a biological response. The link between receptor activation and cellular response is mediated by various effecters. It has been hypothesized that receptors and effecters freely diffuse in the plane of the membrane and that coupling of the two takes place after the agonist-receptor complex has formed [l, 21. Effecters may be ion channels or enzymes (e.g. adenylate cyclase). In the case where they are channels, receptor-mediated permeability changes can arise in two possible ways: (a) the channel effector directly couples to the receptor, and conformational changes in the receptor molecule induced by the agonist result in conformational changes in the effector, thereby altering its permeability; or (b) activation of the receptor indirectly leads to the change in permeability by activating some intracellular metabolic pathway that causes the change. Prolonged exposure of receptors to agonist (over-stimulation) may lead to changes in the receptor, the effector, or the receptor-effector coupling. The result is desensitization which is likely a necessary consequence of activation for many neurotransmitter receptors. Different receptors can interact with common effecters and would therefore cause identical changes within the cell when these receptors are activated. In addition, the same receptor could be linked to different effecters on different cell types and, therefore, upon activation cause changes peculiar to the cell type. It is possible that some receptors for a neurotransmitter lack effecters on certain cell types, and in this case the receptors would be nonfunctioning.

Rubidium efflux from neural cell lines through voltage-dependent potassium channels

Cloned cell lines derived from the rat and mouse nervous systems were screened for the presence of voltage-dependent K+ channels by assaying for an increase in 86Rb+ efflux under depolarizing conditions. Two types of depolarizing stimuli, (a) 100 mM KCl and (b) a combination of veratridine and scorpion venom, produced parallel results in all of 11 excitable cell lines tested; i.e., a cell line either responded to both sets of stimuli (8 examples) or to neither (3 examples). In the case of three cell lines where it was possible to compare the Rb+ efflux results with electrophysiological measurements of K+ currents the two methods gave qualitatively parallel results; i.e., cell lines that exhibited delayed rectification responded positively to depolarization in the Rb+ efflux assay, while cell lines that failed to exhibit K+ currents did not respond in the efflux assay. KCl-induced 86Rb+ efflux from the excitable cell lines did not appear to involve a Ca2+-dependent K+ channel, since efflux was not blocked by lowering extracellular Ca2+ from 2 to 0.1 mM. Efflux also was not blocked by tetraethylammonium or 4-aminopyridine, but could be blocked by scorpion venom. Of 14 cell lines previously classified as glial, 7 failed to show evidence of depolarization-induced 86Rb+ efflux while 7 others responded positively to 100 mM K+. Efflux from the latter 7 lines could be distinguished from efflux from the excitable lines in three ways. (1) Veratridine plus scorpion venom did not stimulate efflux. (2) Scorpion venom did not block KCl-induced efflux. (3) Tetraethylammonium and 4-aminopyridine were effective in blocking KCl-induced efflux from 4 of the 7 lines. These results extend the usefulness of ion flux measurements as a means of assessing the electrical properties of cells and raise some interesting questions concerning the nature of cells that appear to have K+ channels but not Na+ channels.

Depletion layer studies in organic films: Low frequency capacitance measurements in polycrystalline tetracene

The study of the electrical properties of (metal 1‖ organic ‖metal 2) cells has not led to a consistent model of their origin. On the one hand, conductivity measurements suggest that many organic materials behave as insulators (low carrier concentrations) while photovoltaic properties of some of these same materials may be rationalized using the concepts of semiconductor physics, suggesting that the organic film has a high carrier concentration. In this paper the voltage dependence of the capacitance of a (Al‖tetracene‖Au or Nesatron) cell is investigated in an attempt to better understand this contradiction. The electrical properties of this cell are explained in terms of a model in which depletion layers are made from a high density of immobile trapped charge. The trapped charge can be mobilized by light and then evidence is found for a Schottky depletion region (∼2000 Å thick) in the tetracene film.

Development of a sodium/sulphur battery for rail applications

The energy and power requirements of sodium/sulphur batteries to meet three different rail-traction applications are considered. Cell design options to meet these requirements are discussed briefly, and it can be shown that the central-sulphur tube-cell design can meet the requirements of the three rail-traction applications. The design features of a central-sulphur cell design are discussed and data are presented to indicate the state of cell development in terms of cell performance, reliability reproducibility and safety. The electrical properties of cells connected in series/parallel arrays for battery operation are discussed, together with battery thermal management and safety. A practical 10kWh battery comprising 176 cells connected as two 11 × 8 series-parallel arrays has been tested, and problems which can arise from overdischarge, thermal management and electrical short circuits are discussed.

Analysis of the photoelastic effect in ionic crystals

Cells submitted to an electric field gradient experience dielectrophoresis. Such a force is useful for pairing cells prior to electrofusion. The latter event is induced by the application of electric field pulses leading to membrane fusion while cells are in physical contact. Nevertheless, the efficiency of dielectrophoretic pairing and electrofusion of cells are highly dependent on medium properties (osmolarity and conductivity). In this paper, we examine the effect of medium osmolarity on volume, viability and electrical properties of cells. Then we characterize in real time the impact of electropermeabilization of cells on their dielectrophoretic response. To do so, a microfluidic device, inducing particular field topologies is used. These real time observations are correlated to numerical analysis of the Clausius–Mossotti factor. Taking into account the identified changes, an electrofusion protocol adequate to the optimal medium (100 mOsm, 0.03 S/m) is defined. Up to 75% simultaneous binuclear rapid electrofusions were achieved and monitored with average membrane fusion duration lower than 12 s.

Measurement of the Impedance of Frog Skeletal Muscle Fibers

Impedance measurements are necessary to determine the passive electrical properties of cells including the equivalent circuits of the several pathways for current flow. Such measurements are usually made with microelectrodes of high impedance (some 15 MOmega) over a wide frequency range (1-10,000 Hz) and so are subject to many errors. An input amplifier has been developed which has negligible phase shift in this frequency range because it uses negative feedback to keep tiny the voltage on top of the microelectrode. An important source of artifact is the extracellular potential produced by capacitive current flow through the wall of the microelectrodes and the effective resistance of the bathing solution. This artifact is reduced some 10 times by shielding the current microelectrode with a conductive paint. The residual artifact is analyzed, measured, and subtracted from our results. The interelectrode coupling capacitance is reduced below 2 x 10(-17) F and can be neglected. Phase and amplitude measurements are made with phase-sensitive detectors insensitive to noise. The entire apparatus is calibrated at different signal to noise ratios and the nature of the extracellular potential is investigated. The phase shift in the last 5-20 mum of the microelectrode tip is shown to be small and quite independent of frequency under several conditions. Experimental measurements of the phase characteristic of muscle fibers in normal Ringer are presented. The improvements in apparatus and the physiological significance of impedance measurements are discussed. It is suggested that the interpretation of impedance measurements is sensitive to small errors and so it is necessary to present objective evidence of the reliability of one's apparatus and measurements.

Interpretation of some microelectrode measurements of electrical properties of cells.

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