Home About us Contact
|
Home About us Contact | ||
|
|
||
Current Components (current + component)
Selected AbstractsVoltage-gated sodium channel isoform-specific effects of pompilidotoxinsFEBS JOURNAL, Issue 4 2010Emanuele Schiavon Pompilidotoxins (PMTXs, , and ,) are small peptides consisting of 13 amino acids purified from the venom of the solitary wasps Anoplius samariensis (,-PMTX) and Batozonellus maculifrons (,-PMTX). They are known to facilitate synaptic transmission in the lobster neuromuscular junction, and to slow sodium channel inactivation. By using ,-PMTX, ,-PMTX and four synthetic analogs with amino acid changes, we conducted a thorough study of the effects of PMTXs on sodium current inactivation in seven mammalian voltage-gated sodium channel (VGSC) isoforms and one insect VGSC (DmNav1). By evaluating three components of which the inactivating current is composed (fast, slow and steady-state components), we could distinguish three distinct groups of PMTX effects. The first group concerned the insect and Nav1.6 channels, which showed a large increase in the steady-state current component without any increase in the slow component. Moreover, the dose-dependent increase in this steady-state component was correlated with the dose-dependent decrease in the fast component. A second group of effects concerned the Nav1.1, Nav1.2, Nav1.3 and Nav1.7 isoforms, which responded with a large increase in the slow component, and showed only a small steady-state component. As with the first group of effects, the slow component was dose-dependent and correlated with the decrease in the fast component. Finally, a third group of effects concerned Nav1.4 and Nav1.5, which did not show any change in the slow or steady-state component. These data shed light on the complex and intriguing behavior of VGSCs in response to PMTXs, helping us to better understand the molecular determinants explaining isoform-specific effects. [source] Tetanic stimulation of Schaffer collaterals induces rhythmic bursts via NMDA receptor activation in rat CA1 pyramidal neuronsHIPPOCAMPUS, Issue 4 2002Christian Bonansco Abstract Exploring the principles that regulate rhythmic membrane potential (Vm) oscillations and bursts in hippocampal CA1 pyramidal neurons is essential to understanding the , rhythm (,). Recordings were performed in vitro in hippocampal slices from young rats, and a group of the recorded CA1 pyramidal cells were dye-filled with carboxifluorescein and immunolabeled for the R1 subunit of the NMDA receptor. Tetanic stimulation of Schaffer collaterals (SCs) and iontophoresis of glutamate evoked rhythmic Vm oscillations and bursts (,10 mV, ,7 Hz, 2,5 spikes per burst) in cells (31%) placed close to the midline ("medial cells"). Rhythmic bursts remained under picrotoxin (10 ,M) and Vm oscillations persisted with tetrodotoxin (1.5 ,M), but bursts were blocked by AP5 (25 ,M) and Mg2+ -free solutions. Depolarization and AMPA never induced rhythmic bursts. The rest of the neurons (69%), recorded closer to the CA3 region ("lateral cells"), discharged rhythmically single repetitive spikes under SC stimulation and glutamate in control conditions, but fired rhythmic bursts under similar stimulation, both when NMDA was applied and when non-NMDA receptors were blocked with CNQX (20 ,M). Medial cells exhibited a larger NMDA current component and a higher NMDAR1 density at the apical dendritic shafts than lateral cells, suggesting that these differences underlie the dissimilar responses of both cell groups. We conclude that the ",-like" rhythmic oscillations and bursts induced by glutamate and SC stimulation relied on the activation of NMDA receptors at the apical dendrites of medial cells. These results suggest a role of CA3 pyramidal neurons in the generation of CA1 , via the activation of NMDA receptors of CA1 pyramidal neurons. Hippocampus 2002;12:434,446. © 2002 Wiley-Liss, Inc. [source] Effect of Chronic Stress and Mifepristone Treatment on Voltage-Dependent Ca2+ Currents in Rat Hippocampal Dentate GyrusJOURNAL OF NEUROENDOCRINOLOGY, Issue 10 2006N. G. Van Gemert Chronic unpredictable stress affects many properties in rat brain. In the dentate gyrus, among other things, increased mRNA expression of the Ca2+ channel ,1C subunit has been found after 21 days of unpredictable stress in combination with acute corticosterone application (100 nM). In the present study, we examined: (i) whether these changes in expression are accompanied by altered Ca2+ currents in rat dentate granule cells recorded on day 22 and (ii) whether treatment with the glucocorticoid receptor antagonist mifepristone during the last 4 days of the stress protocol normalises the putative stress-induced effects. Three weeks of unpredictable stress did not affect Ca2+ current amplitude in dentate granule cells under basal conditions (i.e. after incubation with vehicle solution). However, the sustained Ca2+ current component (which largely depends on the ,1C subunit) was significantly increased in amplitude after chronic stress when slices had been treated with corticosterone 1,4 h before recording. These findings suggest that dentate granule cells are exposed to an increased calcium load after exposure to an acute stressor when they have a history of chronic stress, potentially leading to increased vulnerability of the cells. The present results are in line with the molecular data on Ca2+ channel ,1C subunit expression. A significant three-way interaction between chronic stress, corticosterone application and mifepristone treatment was found, indicating that the combined effect of stress and corticosterone depends on mifepristone cotreatment. Interestingly, current density (defined as total current divided by capacitance) did not differ between the groups. This indicates that the observed changes in Ca2+ current amplitude could be attributable to changes in cell size. [source] Use of wavelet transform to the method-of-moments matrix arising from electromagnetic scattering problems of 2D objects due to oblique plane-wave incidenceMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2002Jin Yu Abstract An efficient method is presented for transforming the matrix of the method of moments obtained by the expansion of the unknown surface currents with pulse basis function and the use of point match testing to a matrix with wavelet basis and testing functions. When the electromagnetic scattering object is a dielectric or object under oblique plane-wave incidence, more than one equivalent surface current component exists at the object surface. When these currents are connected into one current vector in the method of moments, there must be some discontinuities between the current components. These discontinuities make the direct wavelet transform to the whole MoM matrix inefficient and not equivalent to the use of the wavelet functions in the expansion of the unknown currents and the testing. Therefore, the wavelet transform must be constructed in a different way to avoid these discontinuities. Here, the proper wavelet transform that is equivalent to the use of the wavelet functions in the MoM, which avoids such discontinuities, is presented. This transform is referred to as wavelet subtransform. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 130,134, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10394 [source] Formalin-Induced Short- and Long-Term Modulation of Cav Currents Expressed in Xenopus Oocytes: An In Vitro Cellular Model for Formalin-Induced PainBASIC AND CLINICAL PHARMACOLOGY & TOXICOLOGY, Issue 4 2010Senthilkumar Rajagopal Cav channels were expressed with ,1,1b and ,2, sub-units and the currents (IBa) were studied by voltage clamp. None of the oocytes was dead during the exposure to formalin. Oocyte death was significant between day 1 and day 5 after the exposure to formalin and was uniform among the oocytes expressing various Cav channels. Peak IBa of all Cav and A1, the inactivating current component was decreased whereas the non-inactivated R current was not affected by 5 min. exposure to formalin. On day 1 after the exposure to formalin, Cav1.2c currents were increased, 2.1 and 2.2 currents were decreased and 2.3 currents were unaltered. On day 5, both peak IBa and A1 currents were increased. Cav1.2c, 2.2 and 2.3 currents were increased and Cav2.1 was unaltered on day 10 after the exposure to formalin. Protein kinase C (PKC) may be involved in formalin-induced increase in Cav currents due to the (i) requirement for Cav,1b sub-units; (ii) decreased phorbol-12-myristate,13-acetate potentiation of Cav2.3 currents; (iii) absence of potentiation of Cav2.3 currents following down-regulation of PKC; and (iv) absence of potentiation of Cav2.2 or 2.3 currents with Ser,Ala mutation of Cav,12.2 or 2.3 sub-units. Increased Cav currents and PKC activation may coincide with changes observed in in vivo pain investigations, and oocytes incubated with formalin may serve as an in vitro model for some cellular mechanisms of pain. [source] Elimination Procedure as a Novel and Promising Mathematical Approach in Voltammetric MethodsELECTROANALYSIS, Issue 17-18 2010Nuria Serrano Abstract In the contribution, it has been demonstrated that Elimination Voltammetry with Linear Scan (EVLS) introduces an enhancement of the linear sweep and/or cyclic voltammetric results, and provides information about the type of the currents involved in the considered process. An extension of EVLS has been developed for any combination of scan rates (integers) for six elimination functions that are capable of conserving or eliminating of some voltammetric current components. Simple procedure to obtain the necessary coefficients from the chosen scan rates has been reported. In addition, the calculation and discussion of the relative error of elimination function (REEF) have been presented. The verification of the presented calculations has been done by studying different ratios of scan rates for reduction and oxidation processes of Cd(II) at a hanging mercury drop electrode (HMDE). [source] Independent control of positive- and negative-sequence current components in a doubly fed machineEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 3 2005J. Bendl Abstract This paper analyses the operation of a power unit with a doubly fed machine. A novel vector control method is presented which enables independent control of both positive- and negative-sequence components of stator currents. Also, operation of the system under the condition of unbalanced voltage supply applied to the stator is discussed. Copyright © 2005 John Wiley & Sons, Ltd. [source] On the compensation of non-active current components of three-phase loads with quickly changing unsymmetryEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 5 2001V. Staudt Some types of loads, like arc furnaces, present a special challenge to compensation strategies. They vary quickly and have a very high rated power. For example the arcs of an arc furnace are not burning continuously especially when starting the melting process. This causes variations of the line voltage with frequencies well below the line frequency commonly known as voltage flicker. Because of cost efficiency the energy storage capability of compensators for the mitigation of voltage flicker effects can still only be small compared to the energy taken by the arc furnace during one period of the line voltage. This paper discusses the use of a compensation tool which quickly detects negative sequence current components in comparison to the calculation of an equivalent conductance using the so-called FBD method (Fryze-Buchholz-Depenbrock method). Simulations are used to demonstrate the advantages and disadvantages of the tool for detecting negative sequence current components. It is shown that the quick detection and compensation of negative sequence current components can reduce the amount of voltage flicker considerably. [source] Use of wavelet transform to the method-of-moments matrix arising from electromagnetic scattering problems of 2D objects due to oblique plane-wave incidenceMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2002Jin Yu Abstract An efficient method is presented for transforming the matrix of the method of moments obtained by the expansion of the unknown surface currents with pulse basis function and the use of point match testing to a matrix with wavelet basis and testing functions. When the electromagnetic scattering object is a dielectric or object under oblique plane-wave incidence, more than one equivalent surface current component exists at the object surface. When these currents are connected into one current vector in the method of moments, there must be some discontinuities between the current components. These discontinuities make the direct wavelet transform to the whole MoM matrix inefficient and not equivalent to the use of the wavelet functions in the expansion of the unknown currents and the testing. Therefore, the wavelet transform must be constructed in a different way to avoid these discontinuities. Here, the proper wavelet transform that is equivalent to the use of the wavelet functions in the MoM, which avoids such discontinuities, is presented. This transform is referred to as wavelet subtransform. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 130,134, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10394 [source] Regulation of glucagon release in mouse ,-cells by KATP channels and inactivation of TTX-sensitive Na+ channelsTHE JOURNAL OF PHYSIOLOGY, Issue 3 2000S. O. Göpel 1The perforated patch whole-cell configuration of the patch-clamp technique was applied to superficial glucagon-secreting ,-cells in intact mouse pancreatic islets. 2,-cells were distinguished from the ,- and ,-cells by the presence of a large TTX-blockable Na+ current, a TEA-resistant transient K+ current sensitive to 4-AP (A-current) and the presence of two kinetically separable Ca2+ current components corresponding to low- (T-type) and high-threshold (L-type) Ca2+ channels. 3The T-type Ca2+, Na+ and A-currents were subject to steady-state voltage-dependent inactivation, which was half-maximal at ,45, ,47 and ,68 mV, respectively. 4Pancreatic ,-cells were equipped with tolbutamide-sensitive, ATP-regulated K+ (KATP) channels. Addition of tolbutamide (0·1 mm) evoked a brief period of electrical activity followed by a depolarisation to a plateau of ,30 mV with no regenerative electrical activity. 5Glucagon secretion in the absence of glucose was strongly inhibited by TTX, nifedipine and tolbutamide. When diazoxide was added in the presence of 10 mm glucose, concentrations up to 2 ,m stimulated glucagon secretion to the same extent as removal of glucose. 6We conclude that electrical activity and secretion in the ,-cells is dependent on the generation of Na+ -dependent action potentials. Glucagon secretion depends on low activity of KATP channels to keep the membrane potential sufficiently negative to prevent voltage-dependent inactivation of voltage-gated membrane currents. Glucose may inhibit glucagon release by depolarising the ,-cell with resultant inactivation of the ion channels participating in action potential generation. [source] | |||||||||||||||||||