Positive Voltage Steps Research Articles

A Novel Single-Phase Multilevel High-Gain Inverter With Low Voltage Stress

This article proposes a high performance with 13-step, switched-capacitor multilevel inverter (SCMLI). The gain factor of 6 is achieved, along with self-voltage balancing of capacitors. The suggested structure can be cascaded to generate any number of voltage steps with the inherent property of generating both positive and negative voltage steps. All the power switches withstand voltages lower than 50% of maximum output voltage. The number of power switches, the number of dc input sources, the voltage stress on the switches, and the power losses are reduced. Also, the presented inverter has a minimum cost function compared to the other similar structures. The performance of the proposed 13-step converter has been validated by the simulation, extracted by PSCAD/EMTDC, and also the experimental results, obtained from an implemented laboratory prototype.

Alternating Current Electrophoretic Deposition of Gadolinium Doped Ceria onto Yttrium Stabilized Zirconia: A Study of the Mechanism.

Direct current electrophoretic deposition (DC-EPD) has been successfully adopted to deposit Gd-doped ceria (GDC) onto yttrium stabilized zirconia (YSZ) previously. However, bubble evolution associated with the proton reduction results in deterioration of the quality of the GDC layer. For the purpose of lowering the densification temperature of the GDC layer by improving its green density, alternating current electrophoretic deposition (AC-EPD) is used to eliminate the bubble evolution. A dense GDC layer with a thickness of 6 μm is successfully obtained after sintering at 1250 °C. The barrier layer effectively eliminates the reaction between LaxSr1-xCoyFe1-yO3-δ (LSCF) and YSZ. The voltage waveform consists of a negative voltage step and a positive voltage step of varying magnitude and step length. The optimum frequency of 500 Hz leads to the maximum deposition yield which is linear with regard to deposition time. Moreover, with the increase of the negative to positive voltage ratio and the length of the negative step relative to the length of the positive step, the deposition rate grows correspondingly. Because the AC step voltages result in negligible faradaic reactions, the deposition process is controlled by the transport process and the desorption process, wherein the latter process is irreversible.

Xenopus laevis Oocytes as a Model System for Studying the Interaction Between Asbestos Fibres and Cell Membranes.

The mode of interaction of asbestos fibres with cell membranes is still debatable. One reason is the lack of a suitable and convenient cellular model to investigate the causes of asbestos toxicity. We studied the interaction of asbestos fibres with Xenopus laevis oocytes, using electrophysiological and morphological methods. Oocytes are large single cells, with a limited ability to endocytose molecular ligands; we therefore considered these cells to be a good model for investigating the nature of asbestos/membrane interactions. Electrophysiological recordings were performed to compare the passive electrical membrane properties, and those induced by applying positive or negative voltage steps, in untreated oocytes and those exposed to asbestos fibre suspensions. Ultrastructural analysis visualized in detail, any morphological changes of the surface membrane caused by the fibre treatment. Our results demonstrate that Amosite and Crocidolite-type asbestos fibres significantly modify the properties of the membrane, starting soon after exposure. Cells were routinely depolarized, their input resistance decreased, and the slow outward currents evoked by step depolarizations were dramatically enhanced. Reducing the availability of surface iron contained in the structure of the fibres with cation chelators, abolished these effects. Ultrastructural analysis of the fibre-exposed oocytes showed no evidence of phagocytic events. Our results demonstrate that asbestos fibres modify the oocyte membrane, and we propose that these cells represent a viable model for studying the asbestos/cell membrane interaction. Our findings also open the possibly for finding specific competitors capable of hindering the asbestos-cell membrane interaction as a means of tackling the long-standing asbestos toxicity problem.

Novel coupling is painless

The first report that several neurotransmitters, including γ-aminobutyric acid (GABA), decreased neuronal action potential duration in dorsal root ganglia (DRG) neurons appeared more than 35 years ago (Dunlap and Fischbach, 1978). Dunlap and Fischbach (1978) realized that the effects of GABA could not occur via the ionotropic GABA receptor—at that time the only known GABA receptor—and that the target ion channel was most likely a voltage-gated calcium (CaV) channel, rather than a NaV or KV channel. They correctly concluded that another type of GABA receptor must exist, which we now know is the G protein–coupled GABA type B (GABAB) receptor. The modulated channel was later identified as the chick homologue of the N-type Ca2+ channel CaV2.2 (α1B) (Cox and Dunlap, 1992), one of three members of the CaV2 family. GABAB receptors in human and rodent sensory neurons and in various expression systems were shown subsequently to inhibit native N-current and recombinant CaV2.2 current, respectively (Raingo et al., 2007; Callaghan et al., 2008; Adams and Berecki, 2013). Inhibition primarily occurs by a voltage-dependent mechanism common to various neurotransmitters whereby Gβγ binds to CaV2.2 slowing channel opening, whereas positive voltage steps relieve this inhibition (Marchetti et al., 1986). The closely related P/Q-type (α1A) channel, CaV2.1, exhibits similar modulation by GABA (Mintz and Bean, 1993). The third member of the CaV2 family, CaV2.3 (α1E), is less susceptible to direct Gβγ modulation than the other two family members (Shekter et al., 1997). The revelation that mice with a deletion in either CaV2.2 or in CaV2.3 exhibited reduced neuropathic pain–like behavior, indicating that these channels participate in pain sensation signaling (Saegusa et al., 2000, 2001), sparked great interest in the regulation of CaV2 inhibition by GABAB receptors in DRG neurons. Astonishingly, however, the precise mechanism of GABAB receptor modulation of CaV2.3 channels has remained ill defined.

Allosteric Stabilization of Fully Resting Voltage Sensors by a Tarantula Toxin

The mechanism of a tarantula toxin's action on the voltage gating of a K channel was investigated. An oxidation-resistant variant of guangxitoxin-1E (GxTX) with methionine 35 replaced by norleucine, was synthesized and found to retain biological activity. When applied to voltage-clamped CHO-K1 cells expressing rat Kv2.1, this GxTX was found to shift channel opening to more positive voltages. In response to short stimulating voltage steps, the voltage shift of conductance saturated at micromolar GxTX concentrations. Prolonged or repetitive pulses to positive potentials ejected GxTX from Kv2.1 channels, revealing the decreased affinity of GxTX for activated voltage sensors. GxTX positively shifted Kv2.1 gating currents, and prevented outward gating charge movement at negative voltages. The modulation of gating charge movement indicates that GxTX stabilizes gating charges in their most internal conformation. Single Kv2.1 channels with GxTX bound exhibited a similar unitary conductance as without tarantula toxin, but had an increased latency to first opening in response to positive voltage steps. A diminished mean open time in the presence of GxTX confirms that channel openings occur with toxin bound and suggests a mechanism for the toxin-induced decrease in peak conductance of macroscopic currents. A simple allosteric model was developed where GxTX stabilizes the earliest resting state of voltage sensors. In this model, GxTX binds activated voltage sensors with decreased affinity, and exerts only a feeble destabilizing influence on the dominant open state. The difference in binding affinity between resting and activated voltage sensors suggests potential for development of GxTX as a probe of voltage sensor conformation in living cells.

α5β1 Integrin Engagement Increases Large Conductance, Ca2+-activated K+ Channel Current and Ca2+ Sensitivity through c-src-mediated Channel Phosphorylation

Large conductance, calcium-activated K(+) (BK) channels are important regulators of cell excitability and recognized targets of intracellular kinases. BK channel modulation by tyrosine kinases, including focal adhesion kinase and c-src, suggests their potential involvement in integrin signaling. Recently, we found that fibronectin, an endogenous alpha5beta1 integrin ligand, enhances BK channel current through both Ca(2+)- and phosphorylation-dependent mechanisms in vascular smooth muscle. Here, we show that macroscopic currents from HEK 293 cells expressing murine BK channel alpha-subunits (mSlo) are acutely potentiated following alpha5beta1 integrin activation. The effect occurs in a Ca(2+)-dependent manner, 1-3 min after integrin engagement. After integrin activation, normalized conductance-voltage relations for mSlo are left-shifted at free Ca(2+) concentrations >or=1 microm. Overexpression of human c-src with mSlo, in the absence of integrin activation, leads to similar shifts in mSlo Ca(2+) sensitivity, whereas overexpression of catalytically inactive c-src blocks integrin-induced potentiation. However, neither integrin activation nor c-src overexpression potentiates current in BK channels containing a point mutation at Tyr-766. Biochemical tests confirmed the critical importance of residue Tyr-766 in integrin-induced channel phosphorylation. Thus, BK channel activity is enhanced by alpha5beta1 integrin activation, likely through an intracellular signaling pathway involving c-src phosphorylation of the channel alpha-subunit at Tyr-766. The net result is increased current amplitude, enhanced Ca(2+) sensitivity, and rate of activation of the BK channel, which would collectively promote smooth muscle hyperpolarization in response to integrin-extracellular matrix interactions.

Transient velocity induced by electric injection in blade-plane geometry

Electric charge injection in blade-plane geometry has been widely studied. Previous works on this geometry were carried out with a DC electrical signal. In this paper, a Heaviside step voltage is applied on the device in order to observe the liquid transient behavior. Particle Image Velocimetry (PIV) measurements are performed on negative and positive voltage steps. The transient behavior of the velocity induced by charge injection is discussed for both polarities. The influence of the frequency of an AC square signal is also investigated, and a comparison between AC and DC behaviors is presented.

A Tyrosine Substitution in the Cavity Wall of a K Channel Induces an Inverted Inactivation

Ion permeation and gating kinetics of voltage-gated K channels critically depend on the amino-acid composition of the cavity wall. Residue 470 in the Shaker K channel is an isoleucine, making the cavity volume in a closed channel insufficiently large for a hydrated K+ ion. In the cardiac human ether-a-go-go-related gene channel, which exhibits slow activation and fast inactivation, the corresponding residue is tyrosine. To explore the role of a tyrosine at this position in the Shaker channel, we studied I470Y. The activation became slower, and the inactivation faster and more complex. At +60mV the channel inactivated with two distinct rates (τ1=20ms, τ2=400ms). Experiments with tetraethylammonium and high K+ concentrations suggest that the slower component was of the P/C-type. In addition, an inactivation component with inverted voltage dependence was introduced. A step to −40mV inactivates the channel with a time constant of 500ms. Negative voltage steps do not cause the channel to recover from this inactivated state (τ≫10min), whereas positive voltage steps quickly do (τ=2ms at +60mV). The experimental findings can be explained by a simple branched kinetic model with two inactivation pathways from the open state.

The role of L- and T-type Ca2+ currents during the in vitro aging of murine myogenic (i28) cells in culture

The age-related decline in skeletal muscle strength could, in part, result from alterations in the mechanism of excitation–contraction coupling, responsible for muscle contraction. In the present work, we used the in vitro aging of murine myogenic (i28) cells as a model, to investigate whether the inefficiency of aged satellite cells to generate functional skeletal muscle fibres could be partly due to defective voltage-dependent Ca2+ currents. The whole-cell patch clamp technique was employed to measure L- and T-type Ca2+currents in myotubes derived from the differentiation and fusion of these cells reaching replicative senescence. Our data showed that the expression and the amplitude of these currents decreased significantly during in vitro aging. Moreover, the analysis of the L-type current evoked in young and old cells by positive voltage steps, revealed no differences in the kinetics of activation, but significant alterations in the rate of inactivation. These effects of in vitro aging on voltage-dependent Ca2+ currents could also be related to their inability to fuse into myotubes. Taken together, our data support the hypothesis that age-related effects on voltage-dependent L- and T-type currents could be one of the causes of the failure of satellite cells to efficiently counteract the impairment in muscle force.

Persistent Sodium Current Is a Target for cAMP-Induced Neuronal Plasticity in a State-Setting Modulatory Interneuron

We have identified a TTX-resistant low-threshold persistent inward sodium current in the cerebral giant cells (CGCs) of Lymnaea, an important state-setting modulatory cell type of molluscan feeding networks. This current has slow voltage-dependent activation and de-activation kinetics, ultra-slow inactivation kinetics and fast de-inactivation kinetics. It activates at approximately -90 mV, peaks at approximately -30 mV, reverses at approximately +35 mV and does not show full voltage-dependent inactivation even at positive voltage steps. Lithium-sodium replacement experiments indicate that the persistent sodium current makes a significant contribution to the CGC membrane potential. Injection of cyclic adenosine monophosphate (cAMP) into the CGC cell body produces a large increase in the persistent sodium current that lasts for several hours. cAMP injection also leads to increased bursting, a significant decrease in the resistance and a significant depolarization of the soma membrane, indicating that cAMP-dependent mechanisms induce prolonged neuronal plasticity in the CGCs. Our observations provide the first link between cAMP-mediated modulation of a TTX-resistant persistent sodium current and prolonged neuronal plasticity in an identified modulatory cell type that plays an important role in behavioral state setting.

Voltage-gated potassium currents in rat vas deferens smooth muscle cells.

Voltage-gated components of the outward current in single smooth muscle cells isolated from the epididymal part of the rat vas deferens were studied using amphotericin B perforated patch-clamp techniques. The complex kinetics of the net outward current elicited by positive voltage steps from -80 mV to +40 mV suggested the presence of several components. Bath application of 200 nM charybdotoxin, a potent blocker of large-conductance, Ca(2+)-dependent K(+) channels (BK(Ca)), reduced the current amplitude significantly. When BK(Ca) channels were suppressed, fast-inactivating (I(K,f)) and delayed rectifying (I(K,dr)) components of the outward current were identified. I(K,f) was characterized by fast kinetics of current decay, negative steady-state activation and inactivation dependencies and sensitivity to 4-aminopyridine with an apparent K(d) of 0.32 mM, properties similar to those of the A-type K(+) current. In contrast, I(K,dr) activated and inactivated at more positive potentials. The time constant of activation of I(K,dr) was voltage dependent with an e-fold decrease per 21 mV depolarization. I(K,dr) was inhibited by clofilium, a blocker of voltage-gated K(+) channels, with an IC(50) of 12 micro M and was not blocked by 5 mM 4-aminopyridine. The possible significance of the voltage-gated currents is discussed.

Modulation of perch connexin35 hemi-channels by cyclic AMP requires a protein kinase A phosphorylation site.

Retinal neurons are coupled via gap junctions, which function as electrical synapses that are gated by ambient light conditions. Gap junctions connecting either horizontal cells or AII amacrine cells are inhibited by the neurotransmitter dopamine, via the activation of the cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) signaling pathway. Fish connexin35 (Cx35) and its mouse ortholog, Cx36, are good candidates to undergo dopaminergic modulation, because they have been detected in the inner plexiform layer of the retina, where Type II amacrine cells establish synaptic contacts. We have taken advantage of the ability of certain connexins to form functional connexons (hemi-channels), when expressed in Xenopus oocytes, to investigate whether pharmacological elevation of cAMP modulates voltage-activated hemi-channel currents in single oocytes. Injection of perch Cx35 RNA into Xenopus oocytes induced outward voltage-dependent currents that were recorded at positive membrane potentials. Incubation of oocytes with 8-bromoadenosine 3',5'-cyclic monophosphate (8-Br-cAMP), a membrane permeable cAMP analog, resulted in a dose-dependent and reversible inhibition of hemi-channel currents at the more positive voltage steps. In contrast, treatment with 8-Br-cAMP did not have any effect on hemi-channel currents induced by skate Cx35. Amino acid sequence comparison of the two fish connexins revealed, in the middle cytoplasmic loop of perch Cx35, the presence of a PKA consensus sequence that was absent in the skate connexin. The results obtained with two constructs in which the putative PKA phosphorylation site was either suppressed (perch Cx35R108Q) or introduced (skate Cx35Q108R) indicate that it is responsible for the inhibition of hemi-channel currents. These studies demonstrate that perch Cx35 is a target of the cAMP/PKA signaling pathway and identify a consensus PKA phosphorylation site that is required for channel gating.

Experimental study of the creation of a fire‐rod II: Emissive probe measurements

AbstractA planar electrode (collector) is immersed into a weakly magnetized discharge plasma column. Positive voltage steps are applied to the collector and time resolved measurements of the plasma response are performed by emissive probes using standard boxcar technique. On the emissive probe characteristics an interesting phenomenon is observed: a few μs after the application of the voltage step to the collector (time depends on the distance between the collector and the probe), the emissive probe starts to collect additional positive current in the potential region between plasma potentials of the high and low potential plasma. This phenomenon is investigated experimentally. We give a possible qualitative explanation that additional positive current collection is due to a combination of an interaction between the collector and the probe and space charge effects of positive ions around the probe.

Experimental Study of the Creation of a Fire-rod I: Temporal Development of the Electron Energy Distribution Function

Positive voltage steps are applied to a planar electrode (collector) immersed in a magnetized discharge plasma column with its surface perpendicular to the magnetic field lines. If the voltage step and the neutral gas pressure are high enough additional ionization occurs in front of the collector and a fire-rod is created. Time resolved measurements of the plasma response are performed by a one-sided plane Langmuir probe using standard boxcar technique. The temporal development of the electron energy distribution function after the application of a positive voltage step to the collector is measured by a one-sided plane Langmuir probe. In a magnetized plasma the electron energy distribution function is proportional to the first derivative of a plane Langmuir probe characteristics. It is found that immediately (∼1 μs) after the application of a positive voltage step to the collector a short lifetime electron population is created. This electron population disappears in approximately 2 μs. It is related to the anomalously large initial electron current collected by the collector “current overshoot”. When the initial current overshoot to the collector is terminated, a high potential (anode) plasma starts to form in front of the collector if the voltage step and the pressure are high enough. The formation of the anode plasma electron population is followed experimentally.

L-type Ca(2+) currents overlapping threshold Na(+) currents: could they be responsible for the "slip-mode" phenomenon in cardiac myocytes?

Phosphorylation of Na channels has been suggested to increase their Ca permeability. Termed "slip-mode conductance" (SMC), this hypothesis predicts that Ca influx via protein kinase A (PKA)-modified Na channels can induce sarcoplasmic reticulum (SR) Ca release. We tested this hypothesis by determining if SR Ca release is graded with I(Na) in the presence of activated PKA (with Isoproterenol, ISO). V(m), I(m), and [Ca](i) were measured in feline (n=26) and failing human (n=19) ventricular myocytes. Voltage steps from -70 through -40 mV were used to grade I(Na). Na channel antagonists (tetrodotoxin), L-type Ca channel (I(Ca,L)) antagonists (nifedipine, cadmium, verapamil), and agonists (Bay K 8644, FPL 64176) were used to separate SMC from I(Ca,L). In the absence of ISO, I(Na) was associated with SR Ca release in human but not feline myocytes. After ISO, graded I(Na) was associated with small amounts of SR Ca release in feline myocytes and the magnitude of release increased in human myocytes. I(Na)-related SR Ca release was insensitive to tetrodotoxin (n=10) but was blocked by nifedipine (n=10) and cadmium (n=3). SR Ca release was induced over the same voltage range in the absence of ISO with Bay K 8644 and FPL 64176 (n=9). Positive voltage steps (to 0 mV) to fully activate Na channels (SMC) in the presence of ISO and Verapamil only caused SR Ca release when block of I(Ca,L) was incomplete. We conclude that PKA-mediated increases in I(Ca,L) and SR Ca loading can reproduce many of the experimental features of SMC.

Creation of a firerod by a positive voltage step applied to an anode immersed in a weakly magnetized discharge plasma column

Postive voltage steps are applied to a plane electode immersed in a weakly magnetized discharge plasma column with its surface perpendicular to the magnetic field lines. Voltage steps of different amplitude are applied at various neutral gas pressures. If the amplitude of the voltage step and the neutral gas pressure are high enough, additional discharge occurs in front of the anode and a firerod is created. In this work, time development of the electron distribution function is measured using plane Langmuir probes, cylindrical Langmuir probes and emissive probes. The anode plasma electron population starts to form approximately 3 μs after the voltage step, and is formed in approximately 6–7 μs. The results obtained with the three different types of probes are compared, and found to be very similar.

Long-Lasting GABA-Mediated Depolarization Evoked by High-Frequency Stimulation in Pyramidal Neurons of Rat Hippocampal Slice Is Attributable to a Network-Driven, Bicarbonate-Dependent K+Transient

Biphasic GABAA-mediated postsynaptic responses can be readily evoked in CA1 pyramidal neurons of rat hippocampal slices by high-frequency stimulus (HFS) trains in the presence of ionotropic glutamate receptor antagonists. In the present experiments with sharp microelectrodes, whole-cell techniques, and K+-selective microelectrodes, an HFS train (40 pulses at 100 Hz) applied in stratum radiatum close to the recording site evoked a brief hyperpolarizing IPSP (hIPSP), which turned into a prolonged (2-3 sec) depolarization (GABA-mediated depolarizing postsynaptic potential; GDPSP). The I-V relationships of the postsynaptic currents (hIPSC and GDPSC) had distinct characteristics: the hIPSC and the early GDPSC showed outward rectification, whereas the late GDPSC was reduced with positive voltage steps to zero or beyond (inward rectification), but often no clear reversal was seen. That two distinct currents contribute to the generation of the GDPSP was also evident from the finding that a second HFS train at peak or late GDPSP induced a prompt GABAA-mediated hyperpolarization. The GDPSP/C was dependent on the availability of bicarbonate, but not on interstitial or intrapyramidal carbonic anhydrase activity. The HFS train evoked a rapid GABAA-mediated bicarbonate-dependent increase in the extracellular K+ concentration ([K+]o), and the GDPSP followed the K+ transient in a sub-Nernstian manner. The spatial and pharmacological characteristics of the [K+]o shift indicated that it is generated by a local network of GABAergic interneurons. The brief ascending phase of the GDPSP is linked to a K+-dependent accumulation of intracellular Cl-. Thereafter, a nonsynaptic mechanism, a direct depolarizing effect of the [K+]o shift, is responsible for the most conspicuous characteristics of the GDPSP: its large amplitude and prolonged duration.

Pulsed currents carried by whistlers. IX. In situ measurements of currents disrupted by plasma erosion

In a magnetized laboratory plasma described in the companion paper [Stenzel and Urrutia, Phys. Plasmas 4, 26 (1997)], a large positive voltage step (V≫kTe/e) is applied to electrodes. The current front propagates in the whistler mode in the parameter regime of electron magnetohydrodynamics. The topology of the current density is that of nested helices. Large transient currents in excess of the electron saturation current can be drawn. A transient radial electric field associated with the current rise, excites a compressional, large amplitude, radially outgoing sound wave, which leaves the current channel depleted of plasma. The current collapses due to the density erosion. Electric field reversal excites a rarefaction wave which leads to a partial density and current recovery. Periodic plasma inflow and outflow cause the current to undergo strong relaxation oscillations at a frequency determined by the electrode diameter and the sound speed. In addition, a broad spectrum of microinstabilities is observed in regions of high current density. For drift velocities approaching the thermal speed, the spectrum extends beyond the ion plasma frequency (ωpi) up to the electron plasma frequency (ωpe). Correlation measurements above ωpi reveal modes propagating along the electron drift at speeds above the sound speed but well below the electron drift speed.

Excitation of the Potential Relaxation Instability in a Weakly Magnetized Discharge Plasma by a Voltage Step

AbstractAn instability is triggered in a weakly magnetized discharge plasma by the application of a positive voltage step to a planar collector immersed into the plasma column with its surface perpendicular to the magnetic field lines. Time developement of the plasma density after the application of the pulse is measured by a Langmuir probe. Radial and axial velocity of the plasma density perturbation are measured. Radial velocity is consistent with the increase of the plasma potential in the current channel. Axial velocity is very high. It is interpreted as phase velocity of radial quasiperiodic motion of the plasma in and out of the current channel. Response time of the collector current to the applied voltage step is measured versus different parameters. Experimental results are in agreement with a qualitative model presented in previous work [1] where the observed instability is modeled as a two dimensional potential relaxation instability (PRI). Minor improvements of the previous model are proposed. A rarefaction pulse that moves towards the collector is found as the initial stage of the instability.

Cl? and K+ channel currents during the action potential in Chara. simultaneous recording of membrane voltage and patch currents

Patch currents in the cell attached-mode and action potentials (AP) have been recorded simultaneously in internodal cells of Chara corallina. The action potentials are closely correlated with transient patch currents. With pipettes containing either 50 mM CaCl2 or 100 mM KCl plus 1 or 5 mM CaCl2, these transients measured up to 100 to 200 pA per patch at zero mV. Transients had a mean duration (time during which the current was > or = half maximum peak amplitude) of about 1 sec, a maximum slope for current rising of about 400 pA sec-1 and a maximum rate of about 100 pA sec-1 for current decay, with no obvious effect of external Ca2+ on either of these parameters. In well-resolved recordings of current transients triggered by an action potential (AP), activities of two types of Cl--conducting channels (15 and 38 pS) have been identified. Since activity of these channels was only observed during action potentials but not upon positive voltage steps, these channels are not directly voltage gated but point to a cytoplasmic gating factor which accumulates during excitation and propagates from excited areas to the patch. A K(+)-conducting channel (40 pS) could be identified as well during an AP, when 100 mM KCl was in the pipette solution. The activity of this channel relaxed at the end of the APs with a time constant of about 3 sec. Stimulated activity of this channel is understood to cause the repolarization overshoot during the final phase of the action potential, whereas the transient activation of the Cl- channels determines the fast voltage changes of the action potential.