Guanine nucleotides modulate steady-state inactivation of voltage-gated sodium channels in frog olfactory receptor neurons

1994 ◽  
Vol 142 (1) ◽  
Author(s):  
R.Y.K. Pun ◽  
S.J. Kleene ◽  
R.C. Gesteland
Keyword(s):  
Steady State ◽  
Sodium Channels ◽  
Olfactory Receptor ◽  
Guanine Nucleotides ◽  
Olfactory Receptor Neurons ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Steady State Inactivation ◽  
Receptor Neurons

scholarly journals Properties of transient K+ currents and underlying single K+ channels in rat olfactory receptor neurons.

1991 ◽  
Vol 97 (5) ◽  
pp. 1043-1072 ◽  
Author(s):  
J W Lynch ◽  
P H Barry
Keyword(s):  
Steady State ◽  
Olfactory Receptor ◽  
Olfactory Receptor Neurons ◽  
Simple Method ◽  
Small Component ◽  
Inactivation Curve ◽  
K Channels ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
Receptor Neurons

The transient potassium current, IK(t), of enzymatically dissociated rat olfactory receptor neurons was studied using patch-clamp techniques. Upon depolarization from negative holding potentials, IK(t) activated rapidly and then inactivated with a time course described by the sum of two exponential components with time constants of 22.4 and 143 ms. Single-channel analysis revealed a further small component with a time constant of several seconds. Steady-state inactivation was complete at -20 mV and completely removed at -80 mV (midpoint -45 mV). Activation was significant at -40 mV and appeared to reach a maximum conductance at +40 mV (midpoint -13 mV). Deactivation was described by the sum of two voltage-dependent exponential components. Recovery from inactivation was extraordinarily slow (50 s at -100 mV) and the underlying processes appeared complex. IK(t) was reduced by 4-aminopyridine and tetraethylammonium applied externally. Increasing the external K+ concentration ([K+]o) from 5 to 25 mM partially removed IK(t) inactivation, usually without affecting activation kinetics. The elevated [K+]o also hyperpolarized the steady-state inactivation curve by 9 mV and significantly depolarized the voltage dependence of activation. Single transient K+ channels, with conductances of 17 and 26 pS, were observed in excised patches and often appeared to be localized into large clusters. These channels were similar to IK(t) in their kinetic, pharmacological, and voltage-dependent properties and their inactivation was also subject to modulation by [K+]o. The properties of IK(t) imply a role in action potential repolarization and suggest it may also be important in modulating spike parameters during neuronal burst firing. A simple method is also presented to correct for errors in the measurement of whole-cell resistance (Ro) that can result when patch-clamping very small cells. The analysis revealed a mean corrected Ro of 26 G omega for these cells.

scholarly journals BmK AEP, an Anti-Epileptic Peptide Distinctly Affects the Gating of Brain Subtypes of Voltage-Gated Sodium Channels

2019 ◽  
Vol 20 (3) ◽  
pp. 729 ◽  
Author(s):  
Fan Zhang ◽  
Ying Wu ◽  
Xiaohan Zou ◽  
Qinglian Tang ◽  
Fang Zhao ◽  
...  
Keyword(s):  
Steady State ◽  
Sodium Channels ◽  
Cortical Neurons ◽  
Neuronal Excitability ◽  
Epileptic Activity ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Na Currents ◽  
Ic50 Value ◽  
Steady State Inactivation

BmK AEP, a scorpion peptide purified form the venom of Buthus martensii Karsch, has been reported to display anti-epileptic activity. Voltage-gated sodium channels (VGSCs) are responsible for the rising phase of action potentials (APs) in neurons and, therefore, controlling neuronal excitability. To elucidate the potential molecular mechanisms responsible for its anti-epileptic activity, we examined the influence of BmK AEP on AP firing in cortical neurons and how BmK AEP influences brain subtypes of VGSCs (Nav1.1–1.3 and Nav1.6). BmK AEP concentration-dependently suppresses neuronal excitability (AP firing) in primary cultured cortical neurons. Consistent with its inhibitory effect on AP generation, BmK AEP inhibits Na+ peak current in cortical neurons with an IC50 value of 2.12 µM by shifting the half-maximal voltage of activation of VGSC to hyperpolarized direction by ~7.83 mV without affecting the steady-state inactivation. Similar to its action on Na+ currents in cortical neurons, BmK AEP concentration-dependently suppresses the Na+ currents of Nav1.1, Nav1.3, and Nav1.6, which were heterologously expressed in HEK-293 cells, with IC50 values of 3.20, 1.46, and 0.39 µM with maximum inhibition of 82%, 56%, and 93%, respectively. BmK AEP shifts the voltage-dependent activation in the hyperpolarized direction by ~15.60 mV, ~9.97 mV, and ~6.73 mV in Nav1.1, Nav1.3, and Nav1.6, respectively, with minimal effect on steady-state inactivation. In contrast, BmK AEP minimally suppresses Nav1.2 currents (~15%) but delays the inactivation of the channel with an IC50 value of 1.69 µM. Considered together, these data demonstrate that BmK AEP is a relatively selective Nav1.6 gating modifier which distinctly affects the gating of brain subtypes of VGSCs.

scholarly journals Purification and Characterization of JZTx-14, a Potent Antagonist of Mammalian and Prokaryotic Voltage-Gated Sodium Channels

Toxins ◽  
2018 ◽  
Vol 10 (10) ◽  
pp. 408 ◽  
Author(s):  
Jie Zhang ◽  
Dongfang Tang ◽  
Shuangyu Liu ◽  
Haoliang Hu ◽  
Songping Liang ◽  
...  
Keyword(s):  
Sodium Channels ◽  
Resting State ◽  
Purification And Characterization ◽  
Voltage Gated ◽  
Voltage Gated Sodium Channels ◽  
Steady State Inactivation ◽  
Ic50 Values ◽  
Gating Modifier ◽  
Potent Antagonist

Exploring the interaction of ligands with voltage-gated sodium channels (NaVs) has advanced our understanding of their pharmacology. Herein, we report the purification and characterization of a novel non-selective mammalian and bacterial NaVs toxin, JZTx-14, from the venom of the spider Chilobrachys jingzhao. This toxin potently inhibited the peak currents of mammalian NaV1.2–1.8 channels and the bacterial NaChBac channel with low IC50 values (<1 µM), and it mainly inhibited the fast inactivation of the NaV1.9 channel. Analysis of NaV1.5/NaV1.9 chimeric channel showed that the NaV1.5 domain II S3–4 loop is involved in toxin association. Kinetics data obtained from studying toxin–NaV1.2 channel interaction showed that JZTx-14 was a gating modifier that possibly trapped the channel in resting state; however, it differed from site 4 toxin HNTx-III by irreversibly blocking NaV currents and showing state-independent binding with the channel. JZTx-14 might stably bind to a conserved toxin pocket deep within the NaV1.2–1.8 domain II voltage sensor regardless of channel conformation change, and its effect on NaVs requires the toxin to trap the S3–4 loop in its resting state. For the NaChBac channel, JZTx-14 positively shifted its conductance-voltage (G–V) and steady-state inactivation relationships. An alanine scan analysis of the NaChBac S3–4 loop revealed that the 108th phenylalanine (F108) was the key residue determining the JZTx-14–NaChBac interaction. In summary, this study provided JZTx-14 with potent but promiscuous inhibitory activity on both the ancestor bacterial NaVs and the highly evolved descendant mammalian NaVs, and it is a useful probe to understand the pharmacology of NaVs.

Electrophysiological characteristics of cloned skeletal and cardiac muscle sodium channels

1996 ◽  
Vol 271 (2) ◽  
pp. H498-H506 ◽  
Author(s):  
M. Chahine ◽  
I. Deschene ◽  
L. Q. Chen ◽  
R. G. Kallen
Keyword(s):  
Steady State ◽  
Sodium Channels ◽  
H Infinity ◽  
Hek 293 ◽  
Human Embryonic Kidney Cells ◽  
Current Decay ◽  
Voltage Gated Sodium Channels ◽  
Recovery From Inactivation ◽  
Steady State Inactivation ◽  
Kinetics Of

The alpha-subunit encoding for voltage-gated sodium channels rSkM1 (rat skeletal muscle subtype 1) and hH1 (human heart subtype 1) has been cloned and expressed by various groups under various conditions in Xenopus oocytes and the tsA201 (HEK 293) mammalian cell line derived from human embryonic kidney cells. In this study, we have expressed hH1 and rSkM1 in tsA201 cells for comparison under the same conditions using patch-clamp methods. Our results show significant differences in the current-voltage (I-V) relationship, kinetics of current decay, voltage dependence of steady-state inactivation, and the time constant for recovery from inactivation. We studied several rSkM1/hH1 chimeric sodium channels to identify the structural regions responsible for the different biophysical behavior of the two channel subtypes. Exchanging the interdomain (ID3-4) loops, thought to contain the inactivation particle, between rSkM1 and hH1 had no effect on the electrophysiological behaviors, including inactivation, indicating that the differences in channel subtype characteristics are determined by parts of the channel other than the ID3-4 segment. The data on a chimeric channel in which D1 and D4 are derived from hH1 while D2 and D3 and the ID1-2, ID2-3, and ID3-4 loops are from rSkM1 show that D1 and/or D4 seem to be responsible for the slower kinetics of inactivation of hH1 while D2 and/or D3 appear to contain the determinants for the differences in the I-V relationship, steady-state inactivation (h infinity) curve, and the kinetics of the recovery from inactivation.

scholarly journals Dopamine Reduces Odor- and Elevated-K+-Induced Calcium Responses in Mouse Olfactory Receptor Neurons In Situ

2004 ◽  
Vol 91 (4) ◽  
pp. 1492-1499 ◽  
Author(s):  
Colleen C. Hegg ◽  
Mary T. Lucero
Keyword(s):  
Receptor Antagonist ◽  
Dopamine Receptor ◽  
Olfactory Receptor ◽  
D2 Receptor ◽  
Olfactory Receptor Neurons ◽  
D2 Dopamine Receptor ◽  
Dopamine Receptor Antagonist ◽  
Voltage Gated ◽  
Dopaminergic Modulation ◽  
Receptor Neurons

Although D2 dopamine receptors have been localized to olfactory receptor neurons (ORNs) and dopamine has been shown to modulate voltage-gated ion channels in ORNs, dopaminergic modulation of either odor responses or excitability in mammalian ORNs has not previously been demonstrated. We found that <50 μM dopamine reversibly suppresses odor-induced Ca2+ transients in ORNs. Confocal laser imaging of 300-μm-thick slices of neonatal mouse olfactory epithelium loaded with the Ca2+-indicator dye fluo-4 AM revealed that dopaminergic suppression of odor responses could be blocked by the D2 dopamine receptor antagonist sulpiride (<500 μM). The dopamine-induced suppression of odor responses was completely reversed by 100 μM nifedipine, suggesting that D2 receptor activation leads to an inhibition of L-type Ca2+ channels in ORNs. In addition, dopamine reversibly reduced ORN excitability as evidenced by reduced amplitude and frequency of Ca2+ transients in response to elevated K+, which activates voltage-gated Ca2+ channels in ORNs. As with the suppression of odor responses, the effects of dopamine on ORN excitability were blocked by the D2 dopamine receptor antagonist sulpiride (<500 μM). The observation of dopaminergic modulation of odor-induced Ca2+ transients in ORNs adds to the growing body of work showing that olfactory receptor neurons can be modulated at the periphery. Dopamine concentrations in nasal mucus increase in response to noxious stimuli, and thus D2 receptor-mediated suppression of voltage-gated Ca2+ channels may be a novel neuroprotective mechanism for ORNs.

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