Transient Current Peak Research Articles

A study of the mechanisms of corrosion inhibition of AA2024-T3 by vanadates using the split cell technique

The mechanisms of corrosion inhibition of AA2024-T3 by vanadates were studied in this work using the split cell technique and polarization curves. The electrochemical behavior of clear solutions containing metavanadates and orange solutions containing decavanadates was clearly distinctive. Injection of metavanadates to the cathode side of the different split cell setups greatly reduced the galvanic current, indicating a potent inhibition of the oxygen reduction kinetics. The galvanic current never exhibited a transient current peak, suggesting that metavanadates inhibit AA2024-T3 corrosion by a mechanism that does not involve electrochemical reduction. Injection of metavanadate to the anode side of the different split cells had no effect on the galvanic current. Injection of orange decavanadate to the cathode side of the AA2024-T3 split cell resulted in a large current peak, associated with the electrochemical reduction of decavanadate. However, decavanadates did not impart significant corrosion protection.

Transient substrate currents in junction-isolated lateral IGBT

In this brief, experimental results of transient substrate currents that occur during clamped inductive switching of a junction-isolated lateral insulated gate bipolar transistor are analyzed. The transient substrate current peak at turn off is broader and higher than the value at turn on. The peak substrate current increases with increasing anode voltage, and anode injection efficiency significantly influences the characteristics of the transient currents. Two-dimensional numerical simulations are used to evaluate the internal dynamics of the device. It is shown that the Kirk effect is responsible for the transient currents during the switching of a lateral insulated gate bipolar transistor.

KCachannel insensitivity to Ca2+sparks underlies fractional uncoupling in newborn cerebral artery smooth muscle cells

In smooth muscle cells, localized intracellular Ca2+ transients, termed "Ca2+ sparks," activate several large-conductance Ca2+-activated K+ (KCa) channels, resulting in a transient KCa current. In some smooth muscle cell types, a significant proportion of Ca2+ sparks do not activate KCa channels. The goal of this study was to explore mechanisms that underlie fractional Ca2+ spark-KCa channel coupling. We investigated whether membrane depolarization or ryanodine-sensitive Ca2+ release (RyR) channel activation modulates coupling in newborn (1- to 3-day-old) porcine cerebral artery myocytes. At steady membrane potentials of -40, 0, and +40 mV, mean transient KCa current frequency was approximately 0.18, 0.43, and 0.26 Hz and KCa channel activity [number of KCa channels activated by Ca2+ sparksxopen probability of KCa channels at peak of Ca2+ sparks (NPo)] at the transient KCa current peak was approximately 4, 12, and 24, respectively. Depolarization between -40 and +40 mV increased KCa channel sensitivity to Ca2+ sparks and elevated the percentage of Ca2+ sparks that activated a transient KCa current from 59 to 86%. In a Ca2+-free bath solution or in diltiazem, a voltage-dependent Ca2+ channel blocker, steady membrane depolarization between -40 and +40 mV increased transient KCa current frequency up to approximately 1.6-fold. In contrast, caffeine (10 microM), an RyR channel activator, increased mean transient KCa current frequency but did not alter Ca2+ spark-KCa channel coupling. These data indicate that coupling is increased by mechanisms that elevate KCa channel sensitivity to Ca2+ sparks, but not by RyR channel activation. Overall, KCa channel insensitivity to Ca2+ sparks is a prominent factor underlying fractional Ca2+ spark uncoupling in newborn cerebral artery myocytes.

MEMBRANE DEPOLARIZATION COUPLESCa2+ SPARKS TO KCa CHANNELS IN NEWBORN ARTERIAL SMOOTH MUSCLE CELLS

In arterial smooth muscle cells, localized intracellular Ca2+ transients, termed “Ca2+ sparks”, activate several large-conductance calcium-activated potassium (KCa) channels, resulting in a transient KCa current. In newborn porcine cerebral artery smooth muscle cells, a significant proportion of Ca2+ sparks (~40 %) do not activate a transient KCa current. The goal of this study was to investigate mechanisms that underlie sub-unitary Ca2+ spark to KCa channel coupling in newborn (1–3 day old) porcine cerebral artery smooth muscle cells, and determine if ryanodine-sensitive Ca2+ release (RyR) channel activation or an elevation in KCa channel Ca2+-sensitivity increase coupling. At steady membrane potentials of −40, 0 and +40 mV, mean transient KCa current frequency was 0.18±0.02, 0.42±0.06, and 0.25±0.02 Hz, respectively. At the same potentials, Mean KCa channel activity at the transient KCa current peak (NPO) was 4.2±0.3, 12.1±1.2 and 23.7±3.7, respectively. In diltiazem, a voltage-dependent Ca2+ channel blocker, depolarization between −40 and +40 mV increased mean transient KCa current frequency 1.6–fold. Depolarization over the same voltage range also increased the percentage of Ca2+ sparks that activated a transient KCa current from 59±6 to 86±5%. Although caffeine (10uM), a RyR channel activator,increased mean transient KCa current frequency by 1.5, 1.6 and 1.5-fold at −40, 0 and +40 mV, respectively, caffeine did not alter the percentage of Ca2+ sparks that activated transient KCa current. Data indicate that KCa channel Ca2+-sensitivity, as opposed to RyR channel activity, influences Ca2+ spark to KCa channel coupling in newborn arterial smooth muscle cells.

Design of a Current Sensor for IDDQ Testing of CMOS IC

This study presents the design of an off-chip current sensor for IDDQ testing of CMOS (Complementary Metal-oxide Semiconductor) ICs (integrated circuit). It provides a linear voltage signal of IDDQ current with a conversion factor of 5 mV/μA without any amplification. A voltage-controlled switch is used to bypass the transient current peaks. It has also been shown that the sensor is capable of detecting IDDQ faults of a circuit at 100 kHz test frequency without degrading its performance.

Relocation dynamics of domain boundaries in semiconductor superlattices

The formation of static electric-field domains in doped semiconductor superlattices appears in the current-voltage $(I\ensuremath{-}V)$ characteristics as multiple current branches separated by abrupt discontinuities. The switching dynamics of the charge-accumulation layer forming the domain boundary is experimentally investigated at dc voltages in the first plateau of the $I\ensuremath{-}V$ characteristic for different polarities and amplitudes of the applied voltage steps. When the voltage is decreased (down jumps) from its initial dc value, the accumulation layer can directly move from its initial position to its final position, in accordance with the direction of the applied voltage step. However, when the voltage is increased (up jumps), there are two different modes of the relocation motion of the accumulation layer. For small up jumps, the accumulation layer can still move directly from its initial to its final position. When the amplitude of the transient current peak is above a critical value, a charge dipole is injected at the emitter contact, in addition to the existing monopole formed by the domain boundary. The experimentally observed switching behavior is in excellent qualitative agreement with recent theoretical work [A. Amann et al., Phys. Rev. E 63, 066207 (2001)].

Potent Actions of the Pyrethroid Insecticides Cismethrin and Cypermethrin on Rat Tetrodotoxin-Resistant Peripheral Nerve (SNS/PN3) Sodium Channels Expressed in Xenopus Oocytes

Abstract The rat peripheral nerve tetrodotoxin (TTX)-resistant voltage-sensitive sodium channel (designated SNS/PN3) was expressed in Xenopus laevis oocytes, and the responses of the expressed channels to two pyrethroid insecticides, cismethrin and cypermethrin, were assessed by recording macroscopic sodium currents under voltage clamp conditions. Each pyrethroid produced two distinct modifications of sodium currents carried by SNS/PN3 channels: a sustained, slowly inactivating current evident during a depolarizing pulse and a prominent tail current following repolarization. In addition, high concentrations of cismethrin produced a reduction of the amplitude of the peak transient sodium current. Cismethrin-induced tail currents decayed with a first-order decay constant (τ) of 14.7 ms, whereas cypermethrin-induced tail currents were much more persistent (τ = 558 ms). Modified currents were obtained in the presence of nanomolar concentrations of each compound, and the amplitude of the modified currents exhibited a strong concentration dependence. High concentrations of cismethrin and cypermethrin shifted the voltage dependence of activation of SNS/PN3 sodium channels by ∼5 mV in the direction of hyperpolarization and the voltage dependence of steady-state inactivation by ∼8–10 mV in the direction of depolarization. The high sensitivity of the SNS/PN3 sodium channel to pyrethroids is consistent with the identification of this channel isoform as the principal carrier of the TTX-resistant, pyrethroid-sensitive sodium current of dorsal root ganglion neurons.

Transient breakdown behavior in electron-irradiated and proton-irradiated silicon p–n junctions

We studied the turn-off transient behavior of electron- and proton-irradiated silicon p–n junction diodes. Electron-irradiated n+–p diodes showed transient current peaks at lower reverse voltages. When the forward current was increased, the height and the number of the peaks increased, and at each peak the diode voltage showed a sharp decrease. We explain that the increased ionization coefficients by the electron irradiation caused the current peak to appear during the turn-off transients. p+–n diodes irradiated under the same condition did not show the large peak. This suggests that only the defects in the p-type silicon are responsible for the current peaks.

Current transient analysis of the oxidizing process in the complete anodic regime of the Si–HF system

Potential step experiments from anodic potential to open circuit potential in the electrochemical system Si–HF result in a transient current peaks, provided that oxide was present at the electrode surface. The current transients can be analyzed quantitatively and provide information about the anodic oxide and the electrode processes. In this paper it is shown that the complete I– V-characteristics (including the region of porous silicon layer (PSL) formation) is governed by the oxidation process, that the points of inflection (and not the maxima) indicate changes in electrode processes, and that several linear relations between electrode processes and external parameters can be obtained from evaluating the experiments. The findings are consistent with the view that the electrode processes can be seen as results of the interaction of current bursts which may be synchronized by stochastic processes in time and space and indicate in addition that simple, albeit not yet fully understood mechanisms cause the amazing multitude of phenomena occurring at the Si–liquid interface.

Positive Inotropic Action of NMDA Receptor Antagonist (+)-MK801 in Rat Heart

(+)-MK801, a noncompetitive NMDA receptor antagonist, was reported to exhibit anticonvulsive and neuroprotective activities during the postischemic period. Intravenous administration of (+)-MK801 produced tachycardia in rats, but bradycardia in pigs. We examined the mechanical and electrophysiological effects of (+)-MK801 on rat cardiac tissues. (+)-MK801 dose-dependently increased (3–100 μM) twitch tension in rat atria and ventricular strips. The spontaneous beating rate in rat right atria, however, was dose-dependently decreased by (+)-MK801. The inotropic effect of (+)-MK801 was affected neither by α₁-antagonist (1 μM prazosin) nor by β₁-adrenoceptor antagonist (3 μM atenolol), but significantly by a transient outward K⁺ channel blocker (3 mM 4-aminopyridine). (+)-MK801 did not cause any significant change of intracellular cAMP content. Electrophysiological study in rat ventricular cells revealed that (+)-MK801 concentration-dependently prolonged the action potential duration with a concomitant decrease in the maximum rate of the action potential upstroke (V_max) and an increase in the recovery time constant of V_max. Voltage clamp study showed that (+)-MK801 (3 μM) reduced inward Na⁺ current (I_Na), along with a slowing of its recovery from inactivation and a slight negative shift of its voltage-dependent steady-state inactivation curves. At a much higher concentration (30 μM), (+)-MK801 slightly reduced the amplitude of L-type calcium inward current (I_Ca), although the voltage dependence of its steady-state inactivation was unaffected. For the potassium currents in rat ventricular cells, 3 μM of (+)-MK801 reduced the peak transient outward current (I_to), steady-state outward current (I_ss) and inward current through K₁ channels. The inhibition of I_to was associated with a prominent negative shift in the voltage dependence of its steady-state inactivation curve. The outward current through K₁ channels was unaffected. These results indicate that (+)-MK801 may be a strong I_Na and I_to blocker with some I_Ca blocking activity. The inhibition of I_to and other K⁺ efflux would prolong action potential duration, produce positive inotropic action and contribute to the negative chronotropic effect of (+)-MK801.

Opioid receptor independent effects of morphine on membrane currents in single cardiac myocytes

We have examined the effects of morphine, a mu-opioid receptor agonist, on various membrane ionic currents in rat ventricular and human atrial myocytes, using patch-clamp techniques in the whole-cell configuration. Morphine produced a concentration-dependent reduction in peak transient sodium current. When the sodium current (INa) was evoked at 5-s intervals the estimated IC50 for morphine was approximately 30 mumol litre-1. Morphine 10 mumol litre-1 inhibited INa with a 5-mV shift in the potential-dependent inactivation curve to negative potentials and retarded the INa recovery rate from the inactivated state. Use-dependent INa block was not observed when INa was elicited at frequencies varying from 0.2 to 20 Hz. Morphine did not significantly affect the inward calcium current (ICa), transient outward current (Ito) or the inwardly rectifying potassium current (IK1) at a concentration of 30 mumol litre-1. The inhibitory effect of morphine on INa could not be prevented or reversed by treatment with the opioid antagonist naloxone. Therefore, we suggest that morphine can directly inhibit the Na+ inward current and bind to inactivated Na+ channels.

Transient analysis of capacitance switching for industrial power system by PSpice

Abstract In this paper transient voltages and currents appearing on industrial power systems when the power factor correction capacitor banks are switched in and out are investigated. A numerical software package—PSpice is employed to simulate and analyze the phenomena of switching transients. Results show that the transient current peak would reach several times the nominal capacitor current when the capacitor bank is energized and transient peak voltage across the switch would also reach several times the nominal value when the capacitor bank is disconnected. Techniques for reducing transients on capacitor switching are proposed. The schemes presented are simple and efficient.

Altered Subthreshold Sodium Currents and Disrupted Firing Patterns in Purkinje Neurons of Scn8a Mutant Mice

Sodium currents and action potentials were characterized in Purkinje neurons from ataxic mice lacking expression of the sodium channel Scn8a. Peak transient sodium current was ∼60% of that in normal mice, but subthreshold sodium current was affected much more. Steady-state current elicited by voltage ramps was reduced to ∼30%, and resurgent sodium current, an unusual transient current elicited on repolarization following strong depolarizations, was reduced to 8%–18%. In jolting mice, with a missense mutation in Scn8a, steady-state and resurgent current were also reduced, with altered voltage dependence and kinetics. Both spontaneous firing and evoked bursts of spikes were diminished in cells from null and jolting mice. Evidently Scn8a channels carry most subthreshold sodium current and are crucial for repetitive firing.

Mechanism of anomalous photoinduced transient current peak in amorphous silicon thin-film transistor

The photoinduced transient current from an amorphous silicon thin-film transistor is computed and the mechanism described in terms of trap-state filling dynamics. The direction of the current flow and the location of the transient peak depends strongly on the distributions of donorlike and acceptorlike trap states in the neighborhood of the dark Fermi level. We show that the transient current can flow in the same direction as in the crystalline transistor, as well as in the opposite direction. There is also an interesting cross-over behavior in which the transient current flows out of the drain terminal as a pulse of positive charge, and then immediately reverses its direction. There is a broadening effect of the transient peak by a simultaneous switch on of the gate voltage. The transient peak typically occurs at 10−4 s and an example is provided. The transient current can be greatly diminished by switching the gate voltage long before illumination, or by doping the channel either partially or completely.

Transient current peak and its moisture dependence of PVC containing 1-chloro-2,3-epoxy propane

The mechanisms of the current peak in the current-time characteristics of PVC containing 1-chloro-2,3-epoxy propane have been discussed. The steady state current is found to be greatly affected by temperature. The current is also found to depend strongly on the environmental moisture. Water ions dissociated under the effect of external field are found to promote the carrier creation and not increase the mobility. These charges are deduced to inherently slowly move and accumulate at the electrodes without discharge rather than be trapped at localized defects, which leads to the appearance of the current peak.

External Mg2+Triggers Oscillations and a Subsequent Sustained Level of Intracellular Free Ca2+, Correlated with Changes in Membrane Conductance in the Oocyte of the PrawnPalaemon serratus

We have provided evidence that external Mg2+induces correlated changes in [Ca2+]iand membrane current or potential in prawn oocytes without any requirement of fertilization, using the fluorescent Ca2+indicator Ca green dextran and voltage and current clamp methods. Replacement of Mg2+-free ASW with standard (40 mMMg2+)ASW triggered a diphasic [Ca2+]iresponse consisting of an oscillation period followed by a second state of sustained [Ca2+]ilevel devoid of oscillation, lasting about 70 min and up to 3 hr, respectively. In contrast, oocytes maintained for a long time in Mg2+-free ASW showed no changes in [Ca2+]iwhich remained at a basal concentration of about 0.2 μM.The simultaneous records of [Ca2+]iand membrane or current changes showed that the oscillation period started with a first [Ca2+]ipeak (about 1.7 μM) and was correlated with an initial transient membrane hyperpolarization or a transient initial outward current peak. The first [Ca2+]ipeak was followed by a slow decrease in [Ca2+]ifollowed by a series of [Ca2+]itransients, concurrent with a slow depolarization of the membrane or a related inwardly directed current. The oscillation period ended with an oscillatory plateau of [Ca2+]i(about 0.6 μM) lasting 49.6 ± 4.5 min, the onset of which was concomitant with a final membrane hyperpolarization or a related final outward current. A continuous contact between external Mg2+and the oocyte membrane was necessary to maintain the program of [Ca2+]iand membrane conductance changes. The sources of Ca2+mobilization are of internal origin for both the first peak and the subsequent series of [Ca2+]ioscillations, and are mainly of external origin for the oscillation plateau and for the second state of sustained [Ca2+]ilevel. The first and second step of the cortical reaction occurred during the oscillatory plateau and the second state of sustained [Ca2+]ilevel, respectively.

Membrane Responses Evoked By Organic Buffers In Identified Leech Neurones

Using single-electrode current-clamp and two-electrode voltage-clamp, different identified neurones of the leech (Hirudo medicinalis L.) were shown to hyperpolarize, or to exhibit outward currents (usually >2 nA), during bath application of the organic buffers Mops, Pipes and Mes (10 mmol l-1). Tris and Hepes had little or no effect on the membrane properties of neurones when they were added to a bathing saline buffered by CO2-HCO3- at a constant pH of 7.4. Outward currents evoked by buffers obtained from two suppliers, Roth and Sigma, were not significantly different, except in the case of Pipes. Steady-state currents evoked by Pipes supplied by Roth were eightfold larger than steady-state currents evoked by Pipes from Sigma. A transient current peak always present in responses evoked by Pipes from Roth was never present in responses evoked by Pipes from Sigma. Outward currents evoked by buffers were due to a conductance increase and appeared to be carried by Cl-. In low-Cl- saline, hyperpolarizations evoked by Mops in Retzius cells were reduced. When Cl- was injected into heart motor neurones, the hyperpolarizations evoked by Mops reversed. Tetraethylammonium (TEA+) injected into heart interneurones did not block Mops-evoked hyperpolarizations. Mops-evoked outward currents in Retzius cells were partially blocked by d-tubocurarine and bicuculline methiodide, and the latter also partially blocked Mops-evoked hyperpolarizations in HE cells. Since d-tubocurarine partially blocked acetylcholine-evoked Cl- currents in Retzius cells and bicuculline methiodide partially blocked carbachol-evoked hyperpolarizations in HE cells, Mops appears to act on the cholinergic receptors of these neurones by mediating a Cl- conductance.

Tonic and use-dependent block of sodium currents in isolated cardiac myocytes by bisaramil.

1. The effects of bisaramil on sodium currents in rat isolated cardiac myocytes were examined by use of tight-seal, whole-cell patch clamp techniques. Bisaramil produced a concentration-dependent, readily reversible reduction in peak transient sodium current. When the sodium current was evoked at 3 s intervals the estimated ED50 for bisaramil was about 11 microM. 2. Bisaramil (16 microM) produced a shift in the inactivation curve to hyperpolarized potentials of about 10 mV, but produced no change in the voltage-dependence of activation. 3. The block of the sodium current by bisaramil showed a profound use-dependence. A concentration of 10 microM produced a considerable block of the current with repeated stimulation. The recovery from block was biphasic, showing fast and slow components which had time constants of about 40 ms and 5 s respectively. 4. Bisaramil produced little tonic block of the sodium current at concentrations of 100 microM; at 300 microM it produced tonic block of around 50%, with extreme use-dependence. 5. Bisaramil appeared not to interact primarily with the inactivated form of the channel, since lengthening the depolarizing pulses did not affect the degree of block produced.

Charge displacements in a single potassium ion channel macromolecule during gating

Single ion channel currents can only provide indirect information on channel molecular events (except for timing). In contrast, the electric displacement currents associated with channel gating, termed gating currents, can provide direct information regarding the channel molecule's conformational changes. However, thus far gating currents have been measured only from ensembles of numerous stochastically activated channels and therefore the information they provide is limited. This work presents, for the first time, measurements of gating currents from a single channel molecule. Averaging close to 8000 pre-open currents, aligned to the single channel opening time, enabled the detection of single channel gating currents with a resolution of 2 electron charges. The measured charge displacements show: 1) a slow component, approximately 2 fA above baseline level, assumed to represent stochastic conformational changes, and 2) transients, the most significant of which occur 1.1 and 0.3 ms before channel opening. The transients most likely represent apparent deterministic stages in the gating process. The largest transient current peak was 5.1 +/- 1.6 fA and the total equivalent charge transported across the membrane was 4.7 +/- 2.5 electron charges. This data is unique also in that it presents monitoring of the behavior of a single, well-defined macromolecule.

The toxin helothermine affects potassium currents in newborn rat cerebellar granule cells

Helothermine, a recently isolated toxin from the venom of the Mexican beaded lizard Heloderma horridum horridum was tested on K+ currents of newborn rat cerebellar granule cells. In whole-cell voltage-clamp experiments, cerebellar granule neurons exhibited at least two different K+ current components: a first transient component which is similar to an IA-type current, is characterized by fast activating and inactivating kinetics and blocked by 4-aminopyridine; a second component which is characterized by noninactivating kinetics, is blocked by tetraetylammonium ions and resembles the classical delayed-rectifier current. When added to the standard external solution at concentrations ranging between 0.1 and 2 microM, helothermine reduced the pharmacologically isolated IA-type current component in a voltage- and dose-dependent way, with a half-maximal inhibitory concentration (IC50) of 0.52 microM. A comparison between control and helothermine-modified peak transient currents shows a slowdown of activation and inactivation kinetics. The delayed-rectifier component inhibition was concentration dependent (IC50 = 0.86 microM) but not voltage dependent. No frequency- or use-dependent block was observed on both K+ current types. Perfusing the cells with control solution resulted in quite a complete current recovery. We conclude that helothermine acts with different affinities on two types of K+ current present in central nervous system neurons.