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Charge Movement (charge + movement)
Selected AbstractsIncreased CaV,1a expression with aging contributes to skeletal muscle weaknessAGING CELL, Issue 5 2009Jackson R. Taylor Summary Ca2+ release from the sarcoplasmic reticulum (SR) into the cytosol is a crucial part of excitation,contraction (E-C) coupling. Excitation,contraction uncoupling, a deficit in Ca2+ release from the SR, is thought to be responsible for at least some of the loss in specific force observed in aging skeletal muscle. Excitation,contraction uncoupling may be caused by alterations in expression of the voltage-dependent calcium channel ,1s (CaV1.1) and ,1a (CaV,1a) subunits, both of which are necessary for E-C coupling to occur. While previous studies have found CaV1.1 expression declines in old rodents, CaV,1a expression has not been previously examined in aging models. Western blot analysis shows a substantial increase of CaV,1a expression over the full lifespan of Friend Virus B (FVB) mice. To examine the specific effects of CaV,1a overexpression, a CaV,1a -YFP plasmid was electroporated in vivo into young animals. The resulting increase in expression of CaV,1a corresponded to decline of CaV1.1 over the same time period. YFP fluorescence, used as a measure of CaV,1a -YFP expression in individual fibers, also showed an inverse relationship with charge movement, measured using the whole-cell patch-clamp technique. Specific force was significantly reduced in young CaV,1a -YFP electroporated muscle fibers compared with sham-electroporated, age-matched controls. siRNA interference of CaV,1a in young muscles reduced charge movement, while charge movement in old was restored to young control levels. These studies imply CaV,1a serves as both a positive and negative regulator CaV1.1 expression, and that endogenous overexpression of CaV,1a during old age may play a role in the loss of specific force. [source] Development of a packaging material using antistatic ionomer part 2: charge distributions of potassium ionomerPACKAGING TECHNOLOGY AND SCIENCE, Issue 5 2007Nobuyuki Maki Abstract Generally, plastics and plastic films are low in moisture absorption and high in electric insulation. They are inherently easy to be charged with static and can cause a variety of static troubles. We developed a functional packaging material to solve these static problems, by using potassium ionomer. We reported good antistatic performance (e.g. short static decay time, and excellent ash test) of potassium ionomer films in a previous paper. However, a mechanism underlying the antistatic property of potassium ionomer has not yet been fully elucidated. In this study, we measured the space charge distributions of potassium ionomer using the pulsed electro-acoustic method. As a result of the space charge measurements, we found characteristic charge distribution of potassium ionomer film. On the basis of the existence of this characteristic charge distribution, we speculate that the space electric charge distribution of a potassium ionomer film under a direct current electric field shows apparent electric charge movement. Copyright © 2006 John Wiley & Sons, Ltd. [source] Review of electronic and optical properties of semiconducting ,-conjugated polymers: applications in optoelectronicsPOLYMER INTERNATIONAL, Issue 10 2004André Moliton Abstract A general overview of the optoelectronic properties of ,-conjugated polymers is presented. Two types of polymer are discerned: interchangeable structures of the same energy (degenerate), such as polyacetylene; and non-degenerate polymers, such as poly(para -phenylene). The band structures of degenerate and non-degenerate polymers are related to their conductivities in doped and non-doped states. In both cases, disorder and impurities play an important role in conductivity. Polarons, bipolarons and excitons are detailed with respect to doping and charge transfers. Given the fibrillic nature of these materials, the variable range hopping (VRH) law for semiconducting polymers is modified to account for metallic behaviours. Optoelectronic properties,electroluminescence and photovoltaic activity,are explained in terms of HOMO and LUMO bands, polaron-exciton and charge movement over one or more molecules. The properties of H- or J-type aggregates and their effects on transitions are related to target applications. Device structures of polymer light-emitting diodes are explicitly linked to optimising polaron recombinations and overall quantum efficiencies. The particularly promising use of ,-conjugated polymers in photovoltaic devices is discussed. Copyright © 2004 Society of Chemical Industry [source] The ultrastructural distribution of prestin in outer hair cells: a post-embedding immunogold investigation of low-frequency and high-frequency regions of the rat cochleaEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2010Shanthini Mahendrasingam Abstract Outer hair cells (OHCs) of the mammalian cochlea besides being sensory receptors also generate force to amplify sound-induced displacements of the basilar membrane thus enhancing auditory sensitivity and frequency selectivity. This force generation is attributable to the voltage-dependent contractility of the OHCs underpinned by the motile protein, prestin. Prestin is located in the basolateral wall of OHCs and is thought to alter its conformation in response to changes in membrane potential. The precise ultrastructural distribution of prestin was determined using post-embedding immunogold labelling and the density of the labelling was compared in low-frequency and high-frequency regions of the cochlea. The labelling was confined to the basolateral plasma membrane in hearing rats but declined towards the base of the cells below the nucleus. In pre-hearing animals, prestin labelling was lower in the membrane and also occurred in the cytoplasm, presumably reflecting its production during development. The densities of labelling in low-frequency and high-frequency regions of the cochlea were similar. Non-linear capacitance, thought to reflect charge movements during conformational changes in prestin, was measured in OHCs in isolated cochlear coils of hearing animals. The OHC non-linear capacitance in the same regions assayed in the immunolabelling was also similar in both the apex and base, with charge densities of 10 000/,m2 expressed relative to the lateral membrane area. The results suggest that prestin density, and by implication force production, is similar in low-frequency and high-frequency OHCs. [source] Simultaneous flux and current measurement from single plant protoplasts reveals a strong link between K+ fluxes and current, but no link between Ca2+ fluxes and currentTHE PLANT JOURNAL, Issue 1 2006Matthew Gilliham Summary We present a thorough calibration and verification of a combined non-invasive self-referencing microelectrode-based ion-flux measurement and whole-cell patch clamp system as a novel and powerful tool for the study of ion transport. The system is shown to be capable of revealing the movement of multiple ions across the plasma membrane of a single protoplast at multiple voltages and in complex physiologically relevant solutions. Wheat root protoplasts are patch clamped in the whole-cell configuration and current,voltage relations obtained whilst monitoring net K+ and Ca2+ flux adjacent to the membrane with ion-selective electrodes. At each voltage, net ion flux (nmol m,2 sec,1) is converted to an equivalent current density (mA m,2) taking into account geometry and electrode efficiency, and compared with the net current density measured with the patch clamp system. Using this technique, it is demonstrated that the K+ -permeable outwardly rectifying conductance (KORC) is responsible for net outward K+ movement across the plasma membrane [1:1 flux-to-current ratio (1.21 ± 0.14 SEM, n = 15)]. Variation in the K+ flux-to-current ratio among single protoplasts suggests a heterogeneous distribution of KORC channels on the membrane surface. As a demonstration of the power of the technique we show that despite a significant Ca2+ permeability being associated with KORC (analysis of tail current reversal potentials), there is no correlation between Ca2+ flux and KORC activity. A very significant observation is that large Ca2+ fluxes are electrically silent and probably tightly coupled to compensatory charge movements. This analysis demonstrates that it is mandatory to measure flux and currents simultaneously to investigate properly Ca2+ transport mechanisms and selectivity of ion channels in general. [source] | ||||||||||