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Voltage Changes (voltage + change)
Selected AbstractsElectrophysiological properties of BK channels in Xenopus motor nerve terminalsTHE JOURNAL OF PHYSIOLOGY, Issue 1 2004Xiao-Ping Sun Single channel properties of Ca2+ -activated K+ (BK or Maxi-K) channels have been investigated in presynaptic membranes in Xenopus motoneurone,muscle cell cultures. The occurrence and density of BK channels increased with maturation/synaptogenesis and was not uniform: highest at the release face of bouton-like synaptic varicosities in contact with muscle cells, and lowest in varicosities that did not contact muscle cells. The Ca2+ affinity of the channel (Kd= 7.7 ,m at a membrane potential of +20 mV) was lower than those of BK channels that have been characterized in other terminals. Hill coefficients varied between 1.5 and 2.8 at different potentials and open probability increased e-fold per 16 mV change in membrane potential over a range of [Ca2+]i from 1 ,m to 1 mm. The maximal activation rate of ensembled single BK channel currents was in the submillisecond range at ,+20 mV. The activation rate increased ,10-fold in response to a [Ca2+]i increase from 1 to 100 ,m, but increased only ,2-fold with a voltage change from +20 to +130 mV. The fastest activation kinetics of BK channels in cell-attached patches resembled that in inside-out patches with [Ca2+]i of 100 ,m or more, suggesting that many BK channels are located very close to calcium channels. Given the low Ca2+ affinity and rapid Ca2+ binding/unbinding properties, we conclude that BK channels in this preparation are adapted to play an important role in regulation of neurotransmitter release, and they are ideal reporters of local [Ca2+] at the inner membrane surface. [source] Antagonism of calcium currents and neurotransmitter release by barium ions at frog motor nerve endingsBRITISH JOURNAL OF PHARMACOLOGY, Issue 2 2000Eugene M Silinsky The effects of Ba2+ (0.1,2 mM) on the component of the perineural voltage change associated with nerve terminal calcium currents (prejunctional Ca2+ currents) were compared with the effects of this ion to antagonize calcium-dependent acetylcholine (ACh) release. These experiments were made on isolated neuromuscular junctions of the frog. In the presence of sufficient concentrations of K+ channel blockers to eliminate measurable prejunctional K+ currents, low concentrations of Ba2+ selectively antagonized prejunctional Ca2+ currents in normal Ca2+ solutions. Higher concentrations of Ba2+ also substantially reduced the Na+ component of the perineural waveform. Ba2+ inhibited the prolonged prejunctional Ca2+ currents that developed in the presence of higher concentrations of K+ channel blockers. Simultaneous measurements of the prejunctional Ca2+ currents and the electrophysiological correlates of ACh release (i.e. end-plate potentials, EPPs) were made under conditions of modest K+ channel blockade. Under these conditions, Ba2+ generally produced simultaneous decreases in both Ca2+ currents and EPP amplitudes. In some instances, a prolongation of prejunctional Ca2+ currents and a transient increase in EPP amplitudes preceded the decreases in both electrophysiological events. These results suggest that Ba2+ ions can antagonize the entry of calcium into motor nerve endings and this effect is likely to be responsible for the inhibitory effects of Ba2+ on evoked ACh release. British Journal of Pharmacology (2000) 129, 360,366; doi:10.1038/sj.bjp.0703036 [source] On the kinetics of voltage formation in purple membranes of Halobacterium salinariumFEBS JOURNAL, Issue 19 2000Richard W. Hendler The kinetics of the bacteriorhodopsin photocycle, measured by voltage changes in a closed membrane system using the direct electrometrical method (DEM) of Drachev, L.A., Jasaitus, A.A., Kaulen, A.D., Kondrashin, A.A., Liberman, E.A., Nemecek, I.B., Ostroumov, S.A., Semenov, Yu, A. & Skulachev, V.P. (1974) Nature249, 321,324 are sixfold slower than the kinetics obtained in optical studies with suspensions of purple membrane patches. In this study, we have investigated the reasons for this discrepancy. In the presence of the uncouplers carbonyl cyanide m -chlorophenylhydrazone or valinomycin, the rates in the DEM system are similar to the rates in suspensions of purple membrane. Two alternative explanations for the effects of uncouplers were evaluated: (a) the ,back-pressure' of the ,µ,H+ slows the kinetic steps leading to its formation, and (b) the apparent difference between the two systems is due to slow major electrogenic events that produce little or no change in optical absorbance. In the latter case, the uncouplers would decrease the RC time constant for membrane capacitance leading to a quicker discharge of voltage and concomitant decrease in photocycle turnover time. The experimental results show that the primary cause for the slower kinetics of voltage changes in the DEM system is thermodynamic back-pressure as described by Westerhoff, H.V. & Dancshazy, Z. (1984) Trends Biochem. Sci.9, 112,117. [source] Optimization of output matching network for class F power amplifier according to envelope in the envelope elimination and restoration transmitterMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 8 2010Chongmin Lee Abstract This article presents the design and optimization of output matching network according to envelope for class F power amplifier (PA), which is to apply to envelope elimination and restoration (EER) transmitter. In this article, to increase the PAE of class F PA, which applies to EER transmitter, the varactor diode has been used on output matching network. As envelope changes, it optimizes constitution of harmonic trap that is short circuit in second-harmonic and is open circuit in third-harmonic. When drain voltage changes from 25 V to 30 V, some percentage is improved in the PAE. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 1890,1893, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.25335 [source] Ageing in granular aluminium insulating thin filmsANNALEN DER PHYSIK, Issue 12 2009J. Delahaye Abstract We present a new set of electrical field effect measurements on granular aluminium insulating thin films. We have explored how the conductance relaxations induced by gate voltage changes depend on the age of the system, namely the time elapsed since its quench at low temperature. A clear age dependence of the relaxations is seen, qualitatively similar to ageing effects seen in other well studied glassy systems such as spin glasses or polymers. We explain how our results differ from the previous ones obtained with different protocols in indium oxide and granular aluminium thin films. Our experimental findings bring new information on the dynamics of the system and put new constraints on the theoretical models that may explain slow conductance relaxations in disordered insulators. [source] Electrical and Structural Remodeling in Left Ventricular Hypertrophy,A Substrate for a Decrease in QRS Voltage?ANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 3 2007Ljuba Bacharova M.D., M.B.A., Ph.D. Electrical remodeling in advanced stages of cardiovascular diseases creates a substrate for triggering and maintenance of arrhythmias. The electrical remodeling is a continuous process initiated already in the early stages of cardiological pathology. The aim of this opinion article was to discuss the changes in electrical properties of myocardium in left ventricular hypertrophy (LVH), with special focus on its early stage, as well as their possible reflection in the QRS amplitude of the electrocardiogram. It critically appraises the classical hypothesis related to the QRS voltage changes in LVH. The hypothesis of the relative voltage deficit is discussed in the context of supporting evidence from clinical studies, animal experiments, and simulation studies. The underlying determinants of electrical impulse propagation which may explain discrepancies between "normal" ECG findings and increased left ventricular size/mass in LVH are reviewed. [source] | ||||||||||