scholarly journals Voltage-gated and agonist-mediated rises in intracellular Ca2+ in rat clonal pituitary cells (GH3) held under voltage clamp.

1989 ◽  
Vol 415 (1) ◽  
pp. 143-158 ◽  
Author(s):  
C D Benham
Keyword(s):  
Voltage Clamp ◽  
Pituitary Cells ◽  
Voltage Gated

scholarly journals Determining the Target of Membrane Sterols on the Gating of Voltage-Gated Potassium Channels using Voltage-Clamp Fluorometry

2018 ◽  
Vol 114 (3) ◽  
pp. 477a
Author(s):  
Zakany Florina ◽  
Ferenc Papp ◽  
Gyorgy Panyi ◽  
Zoltan Varga
Keyword(s):  
Potassium Channels ◽  
Voltage Clamp ◽  
Voltage Gated

Two Types of Voltage-Gated K+ Currents in Dissociated Heart Ventricular Muscle Cells of the Snail Lymnaea stagnalis

1999 ◽  
Vol 82 (5) ◽  
pp. 2415-2427 ◽  
Author(s):  
M. S. Yeoman ◽  
P. R. Benjamin
Keyword(s):  
Voltage Clamp ◽  
Action Potentials ◽  
Muscle Cells ◽  
Delayed Rectifier ◽  
Voltage Sensitivity ◽  
Ventricular Muscle ◽  
Current Time ◽  
Voltage Gated ◽  
Time To Peak ◽  
Voltage Dependent

We have used a combination of current-clamp and voltage-clamp techniques to characterize the electrophysiological properties of enzymatically dissociated Lymnaea heart ventricle cells. Dissociated ventricular muscle cells had average resting membrane potentials of −55 ± 5 mV. When hyperpolarized to potentials between −70 and −63 mV, ventricle cells were capable of firing repetitive action potentials (8.5 ± 1.2 spikes/min) that failed to overshoot 0 mV. The action potentials were either simple spikes or more complex spike/plateau events. The latter were always accompanied by strong contractions of the muscle cell. The waveform of the action potentials were shown to be dependent on the presence of extracellular Ca2+ and K+ ions. With the use of the single-electrode voltage-clamp technique, two types of voltage-gated K+ currents were identified that could be separated by differences in their voltage sensitivity and time-dependent kinetics. The first current activated between −50 and −40 mV. It was relatively fast to activate (time-to-peak; 13.7 ± 0.7 ms at +40 mV) and inactivated by 53.3 ± 4.9% during a maintained 200-ms depolarization. It was fully available for activation below −80 mV and was completely inactivated by holding potentials more positive than −40 mV. It was completely blocked by 5 mM 4-aminopyridine (4-AP) and by concentrations of tetraethylammonium chloride (TEA) >10 mM. These properties characterize this current as a member of the A-type family of voltage-dependent K+ currents. The second voltage-gated K+ current activated at more depolarized potentials (−30 to −20 mV). It activated slower than the A-type current (time-to-peak; 74.1 ± 3.9 ms at +40 mV) and showed little inactivation (6.2 ± 2.1%) during a maintained 200-ms depolarization. The current was fully available for activation below −80 mV with a proportion of the current still available for activation at potentials as positive as 0 mV. The current was completely blocked by 1–3 mM TEA. These properties characterize this current as a member of the delayed rectifier family of voltage-dependent K+ currents. The slow activation rates and relatively depolarized activation thresholds of the two K+ currents are suggestive that their main role is to contribute to the repolarization phase of the action potential.

Noise From Voltage-Gated Ion Channels May Influence Neuronal Dynamics in the Entorhinal Cortex

1998 ◽  
Vol 80 (1) ◽  
pp. 262-269 ◽  
Author(s):  
John A. White ◽  
Ruby Klink ◽  
Angel Alonso ◽  
Alan R. Kay
Keyword(s):  
Ion Channels ◽  
Voltage Clamp ◽  
Entorhinal Cortex ◽  
Channel Noise ◽  
Neuronal Dynamics ◽  
Voltage Gated ◽  
Subthreshold Oscillations ◽  
Voltage Dependent ◽  
Voltage Gated Ion Channels ◽  
Gated Ion Channels

White, John A., Ruby Klink, Angel Alonso, and Alan R. Kay. Noise from voltage-gated ion channels may influence neuronal dynamics in the entorhinal cortex. J. Neurophysiol. 80: 262–269, 1998. Neurons of the superficial medial entorhinal cortex (MEC), which deliver neocortical input to the hippocampus, exhibit intrinsic, subthreshold oscillations with slow dynamics. These intrinsic oscillations, driven by a persistent Na+ current and a slow outward current, may help to generate the theta rhythm, a slow rhythm that plays an important role in spatial and declarative learning. Here we show that the number of persistent Na+ channels underlying subthreshold oscillations is relatively small (<104) and use a physiologically based stochastic model to argue that the random behavior of these channels may contribute crucially to cellular-level responses. In acutely isolated MEC neurons under voltage clamp, the mean and variance of the persistent Na+ current were used to estimate the single channel conductance and voltage-dependent probability of opening. A hybrid stochastic-deterministic model was built by using voltage-clamp descriptions of the persistent and fast-inactivating Na+ conductances, along with the fast and slow K+ conductances. All voltage-dependent conductances were represented with nonlinear ordinary differential equations, with the exception of the persistent Na+ conductance, which was represented as a population of stochastic ion channels. The model predicts that the probabilistic nature of Na+ channels increases the cell's repertoire of qualitative behaviors; although deterministic models at a particular point in parameter space can generate either subthreshold oscillations or phase-locked spikes (but rarely both), models with an appropriate level of channel noise can replicate physiological behavior by generating both patterns of electrical activity for a single set of parameters. Channel noise may contribute to higher order interspike interval statistics seen in vitro with DC current stimulation. Models with channel noise show evidence of spike clustering seen in brain slice experiments, although the effect is apparently not as prominent as seen in experimental results. Channel noise may contribute to cellular responses in vivo as well; the stochastic system has enhanced sensitivity to small periodic stimuli in a form of stochastic resonance that is novel (in that the relevant noise source is intrinsic and voltage-dependent) and potentially physiologically relevant. Although based on a simple model that does not include all known membrane mechanisms of MEC stellate cells, these results nevertheless imply that the stochastic nature of small collections of molecules may have important effects at the cellular and network levels.

Space-Clamp Problems When Voltage Clamping Neurons Expressing Voltage-Gated Conductances

2008 ◽  
Vol 99 (3) ◽  
pp. 1127-1136 ◽  
Author(s):  
Dan Bar-Yehuda ◽  
Alon Korngreen
Keyword(s):  
Voltage Clamp ◽  
Reversal Potential ◽  
Voltage Gated ◽  
Cable Theory ◽  
Local Current ◽  
Branching Neurons ◽  
Potential Decay ◽  
Voltage Clamping ◽  
Rat Somatosensory Cortex ◽  
Spherical Cells

The voltage-clamp technique is applicable only to spherical cells. In nonspherical cells, such as neurons, the membrane potential is not clamped distal to the voltage-clamp electrode. This means that the current recorded by the voltage-clamp electrode is the sum of the local current and of axial currents from locations experiencing different membrane potentials. Furthermore, voltage-gated currents recorded from a nonspherical cell are, by definition, severely distorted due to the lack of space clamp. Justifications for voltage clamping in nonspherical cells are, first, that the lack of space clamp is not severe in neurons with short dendrites. Second, passive cable theory may be invoked to justify application of voltage clamp to branching neurons, suggesting that the potential decay is sufficiently shallow to allow spatial clamping of the neuron. Here, using numerical simulations, we show that the distortions of voltage-gated K+ and Ca2+ currents are substantial even in neurons with short dendrites. The simulations also demonstrate that passive cable theory cannot be used to justify voltage clamping of neurons due to significant shunting to the reversal potential of the voltage-gated conductance during channel activation. Some of the predictions made by the simulations were verified using somatic and dendritic voltage-clamp experiments in rat somatosensory cortex. Our results demonstrate that voltage-gated K+ and Ca2+ currents recorded from branching neurons are almost always severely distorted.

scholarly journals Pandinus imperator scorpion venom blocks voltage-gated potassium channels in GH3 cells.

1988 ◽  
Vol 91 (6) ◽  
pp. 817-833 ◽  
Author(s):  
P A Pappone ◽  
M T Lucero
Keyword(s):  
Potassium Channels ◽  
Potassium Channel ◽  
Potassium Current ◽  
Potassium Currents ◽  
Scorpion Venom ◽  
Gh3 Cells ◽  
Pituitary Cells ◽  
Crude Venom ◽  
Voltage Gated ◽  
Voltage Dependent

We examined the effects of Pandinus imperator scorpion venom on voltage-gated potassium channels in cultured clonal rat anterior pituitary cells (GH3 cells) using the gigohm-seal voltage-clamp method in the whole-cell configuration. We found that Pandinus venom blocks the voltage-gated potassium channels of GH3 cells in a voltage-dependent and dose-dependent manner. Crude venom in concentrations of 50-500 micrograms/ml produced 50-70% block of potassium currents measured at -20 mV, compared with 25-60% block measured at +50 mV. The venom both decreased the peak potassium current and shifted the voltage dependence of potassium current activation to more positive potentials. Pandinus venom affected potassium channel kinetics by slowing channel opening, speeding deactivation slightly, and increasing inactivation rates. Potassium currents in cells exposed to Pandinus venom did not recover control amplitudes or kinetics even after 20-40 min of washing with venom-free solution. The concentration dependence of crude venom block indicates that the toxins it contains are effective in the nanomolar range of concentrations. The effects of Pandinus venom were mimicked by zinc at concentrations less than or equal to 0.2 mM. Block of potassium current by zinc was voltage dependent and resembled Pandinus venom block, except that block by zinc was rapidly reversible. Since zinc is found in crude Pandinus venom, it could be important in the interaction of the venom with the potassium channel. We conclude that Pandinus venom contains toxins that bind tightly to voltage-dependent potassium channels in GH3 cells. Because of its high affinity for voltage-gated potassium channels and its irreversibility, Pandinus venom may be useful in the isolation, mapping, and characterization of voltage-gated potassium channels.

scholarly journals Two types of local interneurons are distinguished by morphology, intrinsic membrane properties, and functional connectivity in the moth antennal lobe

2015 ◽  
Vol 114 (5) ◽  
pp. 3002-3013 ◽  
Author(s):  
Masashi Tabuchi ◽  
Li Dong ◽  
Shigeki Inoue ◽  
Shigehiro Namiki ◽  
Takeshi Sakurai ◽  
...  
Keyword(s):  
Gene Expression ◽  
Functional Connectivity ◽  
Sodium Channel ◽  
Voltage Clamp ◽  
Antennal Lobe ◽  
Firing Activity ◽  
Voltage Gated Sodium Channel ◽  
Whole Cell ◽  
Voltage Gated ◽  
Channel Gene

Neurons in the silkmoth antennal lobe (AL) are well characterized in terms of their morphology and odor-evoked firing activity. However, their intrinsic electrical properties including voltage-gated ionic currents and synaptic connectivity remain unclear. To address this, whole cell current- and voltage-clamp recordings were made from second-order projection neurons (PNs) and two morphological types of local interneurons (LNs) in the silkmoth AL. The two morphological types of LNs exhibited distinct physiological properties. One morphological type of LN showed a spiking response with a voltage-gated sodium channel gene expression, whereas the other type of LN was nonspiking without a voltage-gated sodium channel gene expression. Voltage-clamp experiments also revealed that both of two types of LNs as well as PNs possessed two types of voltage-gated potassium channels and calcium channels. In dual whole cell recordings of spiking LNs and PNs, activation of the PN elicited depolarization responses in the paired spiking LN, whereas activation of the spiking LN induced no substantial responses in the paired PN. However, simultaneous recording of a nonspiking LN and a PN showed that activation of the nonspiking LN induced hyperpolarization responses in the PN. We also observed bidirectional synaptic transmission via both chemical and electrical coupling in the pairs of spiking LNs. Thus our results indicate that there were two distinct types of LNs in the silkmoth AL, and their functional connectivity to PNs was substantially different. We propose distinct functional roles for these two different types of LNs in shaping odor-evoked firing activity in PNs.

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