Characterization of a high-voltage-activated IA current with a role in spike timing and locomotor pattern generation

Transient A-type K+ channels (IA) in neurons have been implicated in the delay of the spike onset and the decrease in the firing frequency. Here we have characterized biophysically and pharmacologically an IA current in lamprey locomotor network neurons that is activated by suprathreshold depolarization and is specifically blocked by catechol at 100 μM. The biophysical properties of this current are similar to the mammalian Kv3.4 channel. The role of the IA current both in single neuron firing and in locomotor pattern generation was analyzed. The IA current facilitates Na+ channel recovery from inactivation and thus sustains repetitive firing. The role of the IA current in motor pattern generation was examined by applying catechol during fictive locomotion induced by N-methyl-d-aspartate. Blockade of this current increased the locomotor burst frequency and decreased the firing of motoneurons. Although an alternating motor pattern could still be generated, the cycle duration was less regular, with ventral roots bursts failing on some cycles. Our results thus provide insights into the contribution of a high-voltage-activated IA current to the regulation of firing properties and motor coordination in the lamprey spinal cord.

Lambert-Eaton sera reduce low-voltage and high-voltage activated Ca2+ currents in murine dorsal root ganglion neurons.

Voltage-gated Ca2+ channels are categorized as either high-voltage activated (HVA) or low-voltage activated (LVA), and a subtype (or subtypes) of HVA Ca2+ channels link the presynaptic depolarization to rapid neuro-transmitter release. Reductions in transmitter release are characteristic of the autoimmune disorder, Lambert-Eaton syndrome (LES). Because antibodies from LES patients reduce Ca2+ influx in a variety of cell types and disrupt the intramembrane organization of active zones at neuromuscular synapses, specificity of LES antibodies for the Ca2+ channels that control transmitter release has been suggested as the mechanism for disease. We tested sera from four patients with LES. Serum samples from three of the four patients reduced both the maximal LVA and HVA Ca2+ conductances in murine dorsal root ganglion neurons. Thus, even though LES is expressed as a neuromuscular and autonomic disorder, our studies suggest that Ca2+ channels may be broadly affected in LES patients. To account for the specificity of disease expression, we suggest that incapacitation of only a fraction of the Ca2+ channels clustered at active zones would severely depress transmitter release. In particular, if several Ca2+ channels in a cluster are normally required to open simultaneously before transmitter release becomes likely, the loss of a few active zone Ca2+ channels would exponentially reduce the probability of transmitter release. This model may explain why LES is expressed as a neuromuscular disorder and can account for a clinical hallmark of LES, facilitation of neuromuscular transmission produced by vigorous voluntary effort.

Galvanic Corrosion of High-Temperature Low-Sag (HTLS) High Voltage Conductors: New Materials - New Challenges

High-Temperature Low-Sag (HTLS) high voltage overhead conductors offer higher operating temperatures, reduced resistance and less sag than conventional designs. With up to twice the current capacity for the same diameter conductor, they may help ease the power shortage in the constantly increasing electricity demand, but there might be some concerns about their corrosion resistance. These new conductors use materials relatively new to the power industry, such as advanced carbon fiber polymer matrix composites and unique metal matrix composites/nano-composites predominantly used in aerospace industries. This study has made an initial assessment of potential galvanic corrosion problems in three very different HTLS designs: ACCC (Aluminum Conductor Composite Core), ACCR (Aluminum Conductor Composite Reinforced) and ACSS (Aluminum Conductor Steel Supported). In particular the ACCC design was evaluated for its resistance to corrosion and compared to the other designs. The study concludes that all three designs can develop galvanic corrosion under certain circumstances. While the results are not sufficient to make service life predictions of any of the tested conductors, they point out the necessity of thorough corrosion testing of all new conductor designs.

Transistor current -- voltage relationships : a consideration of high voltage dc operation of junction transistors with special reference to avalanche multiplication and related phenomena /

"August 6, 1963"

Some investigations in the area of high voltage, high current D-C amplifiers /

Issued also as thesis (M.S.) University of Illinois.

High voltage thermionic converters. Prepared under Contract no. AF33(615)-1533

"Project no. 8173, Task no. 817305."

A versatile high-voltage bias supply for extended range MIS C(V) and G(V) measurements /

Includes bibliographical references (p. 61).

High voltage electrical safety orders.

Mode of access: Internet.

Crane, H. Richard "Dick" Experiments - High Voltage Accelerator

Glass Slide #11

Auxiliary subunit regulation of high-voltage activated calcium channels expressed in mammalian cells

The effects of auxiliary calcium channel subunits on the expression and functional properties of high-voltage activated (HVA) calcium channels have been studied extensively in the Xenopus oocyte expression system, but are less completely characterized in a mammalian cellular environment. Here, we provide the first systematic analysis of the effects of calcium channel beta and alpha(2)-delta subunits on expression levels and biophysical properties of three different types (Ca(v)1.2, Ca(v)2.1 and Ca(v)2.3) of HVA calcium channels expressed in tsA-201 cells. Our data show that Ca(v)1.2 and Ca(v)2.3 channels yield significant barium current in the absence of any auxiliary subunits. Although calcium channel beta subunits were in principle capable of increasing whole cell conductance, this effect was dependent on the type of calcium channel alpha(1) subunit, and beta(3) subunits altogether failed to enhance current amplitude irrespective of channel subtype. Moreover, the alpha(2)-delta subunit alone is capable of increasing current amplitude of each channel type examined, and at least for members of the Ca(v)2 channel family, appears to act synergistically with beta subunits. In general agreement with previous studies, channel activation and inactivation gating was regulated both by beta and by alpha(2)-delta subunits. However, whereas pronounced regulation of inactivation characteristics was seen with the majority of the auxiliary subunits, effects on voltage dependence of activation were only small (< 5 mV). Overall, through a systematic approach, we have elucidated a previously underestimated role of the alpha(2)-delta(1) subunit with regard to current enhancement and kinetics. Moreover, the effects of each auxiliary subunit on whole cell conductance and channel gating appear to be specifically tailored to subsets of calcium channel subtypes.

Simulation and Evaluation of High-Voltage Power Systems for Civil Aircraft

A status report of the modelling and simulation work that is being undertaken as part of the TIMES (Totally Integrated More Electric Systems) project is presented. Dynamic power quality simulations have been used to asses the performance of the electrical system of a EMA based actuation system for an Airbus A330 size aircraft, for both low voltage 115 V, and high voltage 230 V three-phase AC systems. The high voltage system is shown to have benefits in terms of power quality and reduced size and weight of equipment.

Danger High Voltage Sign

General note: Title and date provided by Bettye Lane.