scholarly journals Single-Channel Properties of Recombinant Acid-Sensitive Ion Channels Formed by the Subunits Asic2 and Asic3 from Dorsal Root Ganglion Neurons Expressed in Xenopus Oocytes

2001 ◽  
Vol 117 (6) ◽  
pp. 563-572 ◽  
Author(s):  
Ping Zhang ◽  
Cecilia M. Canessa
Keyword(s):  
Dorsal Root Ganglion ◽  
Dorsal Root ◽  
Xenopus Oocytes ◽  
Single Channel ◽  
Dorsal Root Ganglion Neurons ◽  
Channel Current ◽  
Single Channel Current ◽  
The Mean ◽  
Ganglion Neurons ◽  
Channel Properties

The acid-sensitive ion channels known as ASIC are gated by external protons. A set of these channels is expressed in dorsal root ganglion neurons where they may participate in the transduction of mechanical and nociceptive stimuli. Here, we have examined the single-channel properties of channels formed by the subunits ASIC2 and ASIC3 expressed in Xenopus oocytes using outside-out patches. The mean single-channel current-voltage relationship is linear with a slope conductance of 18 pS between −80 and −40 mV in 150 mM Na+ outside and 150 mM K+ inside the patch pipet. The selectivity for monovalent cations has the sequence Na+ > Li+ > K+. Divalent cations such as Ca2+ do not permeate, but instead block the channel when applied to the extracellular side. External protons increase the probability of channels being open to a maximum of 0.8 with an EC50 of 16 ± 4 μM and a Hill coefficient of 2.7 ± 0.3, whereas the mean single-channel current amplitude is independent of external pH. Analysis of the kinetics of single channels indicates the presence of at least four modes of activity (Mod1 to Mod4) in addition to an inactivated state. Three of the modes exhibit distinct kinetics, and can be unambiguously identified on the basis of open probability (PoMod1 = 0.5 ± 0.05; PoMod2 > 0.9 ± 0.05; PoMod3 < 0.1). Mode 4, which has a Po in the range of 0.5–0.8, may constitute a distinct mode or alternatively, it represents transitions between the other three modes of activity. Increasing [H+]o increases the frequency of entering the modes with high Po (modes 1, 2, and 4) and the time the channel spends in the modes with high activity.

scholarly journals Paclitaxel Increases High Voltage^|^ndash;Dependent Calcium Channel Current in Dorsal Root Ganglion Neurons of the Rat

2012 ◽  
Vol 120 (3) ◽  
pp. 187-195 ◽  
Author(s):  
Kazuyoshi Kawakami ◽  
Terumasa Chiba ◽  
Nobuyuki Katagiri ◽  
Maya Saduka ◽  
Kenji Abe ◽  
...  
Keyword(s):  
Dorsal Root Ganglion ◽  
Calcium Channel ◽  
High Voltage ◽  
Dorsal Root ◽  
Dorsal Root Ganglion Neurons ◽  
Channel Current ◽  
Ganglion Neurons

GABA-Induced Cl− Current in Cultured Embryonic Human Dorsal Root Ganglion Neurons

1999 ◽  
Vol 82 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Alexander Y. Valeyev ◽  
John C. Hackman ◽  
Alice M. Holohean ◽  
Patrick M. Wood ◽  
Jennifer L. Katz ◽  
...  
Keyword(s):  
Dorsal Root Ganglion ◽  
Dorsal Root ◽  
Single Channel ◽  
Dorsal Root Ganglion Neurons ◽  
Hill Coefficient ◽  
Equilibrium Potential ◽  
Single Channels ◽  
Drg Neurons ◽  
Whole Cell ◽  
Ganglion Neurons

γ-Aminobutyric acid (GABA)-activated channels in embryonic (5–8 wk old) human dorsal root ganglion (DRG) neurons in dissociated culture were characterized by whole cell and single-channel techniques. All DRG neurons when held at negative holding membrane potentials displayed inward current to micromolar concentrations of GABA applied by pressure pulses from closely positioned micropipettes. The current was directly proportional to the concentration of GABA (EC50, 111 μM; Hill coefficient, 1.7). DRG neurons also responded to micromolar concentrations of pentobarbital and alphaxalone but not to cis-4-aminocrotonic acid (CACA), glycine, or taurine. Baclofen (100 μM) affected neither the holding currents nor K+ conductance (when patch pipettes were filled with 130 mM KCl) caused by depolarizing pulses. Whole cell GABA-currents were blocked by bicuculline, picrotoxin, and t-butylbicyclophosphorothionate (TBPS; all at 100 μM). The reversal potential of whole cell GABA-currents was close to the theoretical Cl− equilibrium potential, shifting with changes in intracellular Cl− concentration in a manner expected for Cl−-selective channels. The whole cell I-V curve for GABA-induced currents demonstrated slight outward rectification with nearly symmetrical outside and inside Cl− concentrations. Spectral analysis of GABA-induced membrane current fluctuations showed that the kinetic components were best fitted by a triple Lorentzian function. The apparent elementary conductance for GABA-activated Cl− channels determined from the power spectra was 22.6 pS. Single-channel recordings from cell-attached patches with pipettes containing 10 μM GABA indicated that GABA-activated channels have a main and a subconductance level with values of 30 and 19 pS, respectively. Mean open and closed times of the channel were characterized by two or three exponential decay functions, suggesting two or three open channel states and two closed states. Single channels showed a lack of rectification. The actions of GABA on cultured human embryonic DRG neurons are mediated through the activation of GABAA receptors with properties corresponding to those found in the CNS of human and other mammalian species but differing from those of cultured human adult DRG neurons.

Axotomy- and Autotomy-Induced Changes in Ca2+and K+ Channel Currents of Rat Dorsal Root Ganglion Neurons

2001 ◽  
Vol 85 (2) ◽  
pp. 644-658 ◽  
Author(s):  
Fuad A. Abdulla ◽  
Peter A. Smith
Keyword(s):  
Dorsal Root Ganglion ◽  
Dorsal Root ◽  
Low Voltage ◽  
Cell Types ◽  
Dorsal Root Ganglion Neurons ◽  
Small Cells ◽  
K Channel ◽  
Delayed Rectifier ◽  
Channel Current ◽  
Ganglion Neurons

Sciatic nerve section (axotomy) increases the excitability of rat dorsal root ganglion (DRG) neurons. The changes in Ca2+ currents, K+ currents, Ca2+-sensitive K+ current, and hyperpolarization-activated cation current ( I H) that may be associated with this effect were examined by whole cell recording. Axotomy affected the same conductances in all types of DRG neuron. In general, the largest changes were seen in “small” cells and the smallest changes were seen in “large” cells. High-voltage–activated Ca2+-channel current (HVA- I Ba) was reduced by axotomy. Although currents recorded in axotomized neurons exhibited increased inactivation, this did not account for all of the reduction in HVA- I Ba. Activation kinetics were unchanged, and experiments with nifedipine and/or ω-conotoxin GVIA showed that there was no change in the percentage contribution of L-type, N-type, or “other” HVA- I Bato the total current after axotomy. T-type (low-voltage–activated) I Ba was not affected by axotomy. Ca2+-sensitive K+conductance ( g K,Ca) appeared to be reduced, but when voltage protocols were adjusted to elicit similar amounts of Ca2+ influx into control and axotomized cells, I K,Ca(s) were unchanged. After axotomy, Cd2+-insensitive, steady-state K+ channel current, which primarily comprised delayed rectifier K+ current ( I K), was reduced by about 60% in small, medium, and large cells. These data suggest that axotomy-induced increases in excitability are associated with decreases in I K and/or decreases in g K,Ca that are secondary to decreased Ca2+-influx. Because I H was reduced by axotomy, changes in this current do not contribute to increased excitability. The amplitude and inactivation of I Ba in all cell types was changed more profoundly in animals that exhibited self-mutilatory behavior (autotomy). The onset of this behavior corresponded with significant reduction in I Ba of large neurons. This finding supports the hypothesis that autotomy, that may be related to human neuropathic pain, is associated with changes in the properties of large myelinated sensory neurons.

scholarly journals Single Channel Properties of P2X2 Purinoceptors

1999 ◽  
Vol 113 (5) ◽  
pp. 695-720 ◽  
Author(s):  
Shinghua Ding ◽  
Frederick Sachs
Keyword(s):  
Conformational Changes ◽  
Single Channel ◽  
Excess Noise ◽  
Hill Coefficient ◽  
Inward Rectification ◽  
Channel Current ◽  
Single Channel Current ◽  
The Mean ◽  
Single Channel Currents ◽  
Channel Properties

The single channel properties of cloned P2X2 purinoceptors expressed in human embryonic kidney (HEK) 293 cells and Xenopus oocytes were studied in outside-out patches. The mean single channel current–voltage relationship exhibited inward rectification in symmetric solutions with a chord conductance of ∼30 pS at −100 mV in 145 mM NaCl. The channel open state exhibited fast flickering with significant power beyond 10 kHz. Conformational changes, not ionic blockade, appeared responsible for the flickering. The equilibrium constant of Na+ binding in the pore was ∼150 mM at 0 mV and voltage dependent. The binding site appeared to be ∼0.2 of the electrical distance from the extracellular surface. The mean channel current and the excess noise had the selectivity: K+ > Rb+ > Cs+ > Na+ > Li+. ATP increased the probability of being open (Po) to a maximum of 0.6 with an EC50 of 11.2 μM and a Hill coefficient of 2.3. Lowering extracellular pH enhanced the apparent affinity of the channel for ATP with a pKa of ∼7.9, but did not cause a proton block of the open channel. High pH slowed the rise time to steps of ATP without affecting the fall time. The mean single channel amplitude was independent of pH, but the excess noise increased with decreasing pH. Kinetic analysis showed that ATP shortened the mean closed time but did not affect the mean open time. Maximum likelihood kinetic fitting of idealized single channel currents at different ATP concentrations produced a model with four sequential closed states (three binding steps) branching to two open states that converged on a final closed state. The ATP association rates increased with the sequential binding of ATP showing that the binding sites are not independent, but positively cooperative. Partially liganded channels do not appear to open. The predicted Po vs. ATP concentration closely matches the single channel current dose–response curve.

TREK-2 (K2P10.1) and TRESK (K2P18.1) are major background K+ channels in dorsal root ganglion neurons

2006 ◽  
Vol 291 (1) ◽  
pp. C138-C146 ◽  
Author(s):  
Dawon Kang ◽  
Donghee Kim
Keyword(s):  
Dorsal Root Ganglion ◽  
Dorsal Root ◽  
Single Channel ◽  
Active Role ◽  
Dorsal Root Ganglion Neurons ◽  
Pcr Analysis ◽  
Drg Neurons ◽  
Ganglion Neurons ◽  
Pore Domain ◽  
Inside Out

Dorsal root ganglion (DRG) neurons express mRNAs for many two-pore domain K+ (K2P) channels that behave as background K+ channels. To identify functional background K+ channels in DRG neurons, we examined the properties of single-channel openings from cell-attached and inside-out patches from the cell bodies of DRG neurons. We found seven types of K+ channels, with single-channel conductance ranging from 14 to 120 pS in 150 mM KCl bath solution. Four of these K+ channels showed biophysical and pharmacological properties similar to TRESK (14 pS), TREK-1 (112 pS), TREK-2 (50 pS), and TRAAK (73 pS), which are members of the K2P channel family. The molecular identity of the three other K+ channels could not be determined, as they showed low channel activity and were observed infrequently. Of the four K2P channels, the TRESK-like (14 pS) K+ channel was most active at 24°C. At 37°C, the 50-pS (TREK-2 like) channel was the most active and contributed the most (69%) to the resting K+ current, followed by the TRESK-like 14-pS (16%), TREK-1-like 112-pS (12%), and TRAAK-like 73-pS (3%) channels. In DRG neurons, mRNAs of all four K2P channels, as well as those of TASK-1 and TASK-3, were expressed, as judged by RT-PCR analysis. Our results show that TREKs and TRESK together contribute >95% of the background K+ conductance of DRG neurons at 37°C. As TREKs and TRESK are targets of modulation by receptor agonists, they are likely to play an active role in the regulation of excitability in DRG neurons.

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