Voltage-Gated Potassium Channels Activated During Action Potentials in Layer V Neocortical Pyramidal Neurons

2000 ◽  
Vol 83 (1) ◽  
pp. 70-80 ◽  
Author(s):  
Jian Kang ◽  
John R. Huguenard ◽  
David A. Prince
Keyword(s):  
Potassium Channels ◽  
Action Potentials ◽  
Pyramidal Neurons ◽  
Bk Channels ◽  
Repetitive Firing ◽  
Delayed Rectifier ◽  
Voltage Gated ◽  
Voltage Dependent ◽  
Layer V ◽  
Neocortical Pyramidal Neurons

To investigate voltage-gated potassium channels underlying action potentials (APs), we simultaneously recorded neuronal APs and single K+ channel activities, using dual patch-clamp recordings (1 whole cell and 1 cell-attached patch) in single-layer V neocortical pyramidal neurons of rat brain slices. A fast voltage-gated K+ channel with a conductance of 37 pS (Kf) opened briefly during AP repolarization. Activation of Kf channels also was triggered by patch depolarization and did not require Ca2+influx. Activation threshold was about −20 mV and inactivation was voltage dependent. Mean duration of channel activities after single APs was 6.1 ± 0.6 ms (mean ± SD) at resting membrane potential (−64 mV), 6.7 ± 0.7 ms at −54 mV, and 62 ± 15 ms at −24 mV. The activation and inactivation properties suggest that Kf channels function mainly in AP repolarization but not in regulation of firing. Kf channels were sensitive to a low concentration of tetraethylammonium (TEA, 1 mM) but not to charybdotoxin (ChTX, 100 nM). Activities of A-type channels (KA) also were observed during AP repolarization. KA channels were activated by depolarization with a threshold near −45 mV, suggesting that KA channels function in both repolarization and timing of APs. Inactivation was voltage dependent with decay time constants of 32 ± 6 ms at −64 mV (rest), 112 ± 28 ms at −54 mV, and 367 ± 34 ms at −24 mV. KA channels were localized in clusters and were characterized by steady-state inactivation, multiple subconductance states (36 and 19 pS), and inhibition by 5 mM 4-aminopyridine (4-AP) but not by 1 mM TEA. A delayed rectifier K+ channel (Kdr) with a unique conductance of 17 pS was recorded from cell-attached patches with TEA/4-AP-filled pipettes. Kdrchannels were activated by depolarization with a threshold near −25 mV and showed delayed long-lasting activation. Kdr channels were not activated by single action potentials. Large conductance Ca2+-activated K+ (BK) channels were not triggered by neuronal action potentials in normal slices and only opened as neuronal responses deteriorated (e.g., smaller or absent spikes) and in a spike-independent manner. This study provides direct evidence for different roles of various K+ channels during action potentials in layer V neocortical pyramidal neurons. Kf and KA channels contribute to AP repolarization, while KA channels also regulate repetitive firing. Kdr channels also may function in regulating repetitive firing, whereas BK channels appear to be activated only in pathological conditions.

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.

Zinc and Copper Influence Excitability of Rat Olfactory Bulb Neurons by Multiple Mechanisms

2001 ◽  
Vol 86 (4) ◽  
pp. 1652-1660 ◽  
Author(s):  
Michelle S. Horning ◽  
Paul Q. Trombley
Keyword(s):  
Ion Channels ◽  
Potassium Channels ◽  
Olfactory Bulb ◽  
Membrane Potentials ◽  
Repetitive Firing ◽  
Delayed Rectifier ◽  
Voltage Gated ◽  
Voltage Gated Ion Channels ◽  
Olfactory Bulb Neurons ◽  
Gated Ion Channels

Zinc and copper are highly concentrated in several mammalian brain regions, including the olfactory bulb and hippocampus. Whole cell electrophysiological recordings were made from rat olfactory bulb neurons in primary culture to compare the effects of zinc and copper on synaptic transmission and voltage-gated ion channels. Application of either zinc or copper eliminated GABA-mediated spontaneous inhibitory postsynaptic potentials. However, in contrast to the similarity of their effects on inhibitory transmission, spontaneous glutamate-mediated excitatory synaptic activity was completely blocked by copper but only inhibited by zinc. Among voltage-gated ion channels, zinc or copper inhibited TTX-sensitive sodium channels and delayed rectifier-type potassium channels but did not prevent the firing of evoked single action potentials or dramatically alter their kinetics. Zinc and copper had distinct effects on transient A-type potassium currents. Whereas copper only inhibited the A-type current, zinc modulation of A-type currents resulted in either potentiation or inhibition of the current depending on the membrane potential. The effects of zinc and copper on potassium channels likely underlie their effects on repetitive firing in response to long-duration step depolarizations. Copper reduced repetitive firing independent of the initial membrane voltage. In contrast, whereas zinc reduced repetitive firing at membrane potentials associated with zinc-mediated enhancement of the A-type current (−50 mV), in a significant proportion of neurons, zinc increased repetitive firing at membrane potentials associated with zinc-mediated inhibition of the A-type current (−90 mV). Application of zinc or copper also inhibited voltage-gated Ca2+ channels, suggesting a possible role for presynaptic modulation of neurotransmitter release. Despite similarities between the effects of zinc and copper on some ligand- and voltage-gated ion channels, these data suggest that their net effects likely contribute to differential modulation of neuronal excitability.

scholarly journals GABAA Mediated Afterdepolarization in Pyramidal Neurons From Rat Neocortex

1997 ◽  
Vol 77 (2) ◽  
pp. 1039-1045 ◽  
Author(s):  
R. Cerne ◽  
W. J. Spain
Keyword(s):  
Action Potentials ◽  
Pyramidal Neurons ◽  
Brain Slices ◽  
Apical Dendrite ◽  
Dependent Manner ◽  
Voltage Dependent ◽  
Rat Neocortex ◽  
Layer V ◽  
Current Steps ◽  
Intense Activity

Cerne, R. and W. J. Spain. A GABAA mediated afterdepolarization in pyramidal neurons from rat neocortex. J. Neurophysiol. 77: 1039–1045, 1997. We report a novel slow afterdepolarization (sADP) in layer V pyramidal neurons when brain slices from somatosensory cortex are perfused with γ-aminobutyric acid (GABA). Whole cell recordings were made from visually identified neurons in slices from 3- to 5-wk-old rats. The firing of action potentials at 100 Hz for 1 s, evoked by a train of brief current pulses, typically is followed by a slow afterhyperpolarization (sAHP). When GABA (1 mM) was applied to the perfusate, the sAHP was replaced by a sADP of ≈18 mV in amplitude, which on average lasted for 26 s. The sADP was not evoked or terminated as an all-or-none event: it grew in amplitude and duration as the number of evoked action potentials was increased; and when the sADP was interrupted with hyperpolarizing current steps, its amplitude and duration were graded in a time- and voltage-dependent manner. The sADP did not depend on Ca2+ entry into the cell: it could be evoked when bath Ca2+ was replaced by Mn2+ or in neurons dialyzed with 20 mM bis-( o-aminophenoxy)- N,N,N′,N′-tetraacetic acid. We hypothesized that the sADP was generated predominantly in the dendrites because it was associated with the firing of small-amplitude action potentials that continued after the somatic membrane potential was repolarized to −70 mV by steady current injection. We tested this hypothesis by evoking the sADP in neurons with surgically amputated apical dendrites. In those neurons, the average duration of the sADP was 78% shorter than in neurons with an intact apical dendrite and there were no associated small action potentials. The sADP also was evoked by muscimol, but not by baclofen, and was blocked by bicuculline or picrotoxin but not by CGP 35348, indicating that it is mediated through the activation of GABAA receptors. Our results suggest that intense activity in the presence of GABA results in a long-lasting enhancement of excitability in the apical dendrite that in turn could lead to amplification of distal excitatory synaptic potentials.

Stimulation of 5-HT2 Receptors in Prefrontal Pyramidal Neurons Inhibits Cav1.2 L-Type Ca2+Currents Via a PLCβ/IP3/Calcineurin Signaling Cascade

2002 ◽  
Vol 87 (5) ◽  
pp. 2490-2504 ◽  
Author(s):  
Michelle Day ◽  
Patricia A. Olson ◽  
Josef Platzer ◽  
Joerg Striessnig ◽  
D. James Surmeier
Keyword(s):  
Pyramidal Neurons ◽  
Inositol Trisphosphate ◽  
Cell Voltage ◽  
Signaling Cascade ◽  
Channel Modulation ◽  
Receptor Modulation ◽  
Bath Application ◽  
Voltage Dependent ◽  
Intracellular Ca ◽  
Layer V

There is growing evidence linking alterations in serotonergic signaling in the prefrontal cortex to the etiology of schizophrenia. Prefrontal pyramidal neurons are richly innervated by serotonergic fibers and express high levels of serotonergic 5-HT2-class receptors. It is unclear, however, how activation of these receptors modulates cellular activity. To help fill this gap, whole cell voltage-clamp and single-cell RT-PCR studies of acutely isolated layer V–VI prefrontal pyramidal neurons were undertaken. The vast majority (>80%) of these neurons had detectable levels of 5-HT2A or 5-HT2C receptor mRNA. Bath application of 5-HT2 agonists inhibited voltage-dependent Ca2+ channel currents. L-type Ca2+ channels were a particularly prominent target of this signaling pathway. The L-type channel modulation was blocked by disruption of Gαq signaling or by inhibition of phospholipase Cβ. Antagonism of intracellular inositol trisphosphate signaling, chelation of intracellular Ca2+, or depletion of intracellular Ca2+ stores also blocked this modulation. Inhibition of the Ca2+-dependent phosphatase calcineurin prevented receptor-mediated modulation of L-type currents. Last, the 5-HT2 receptor modulation was robustly expressed in neurons from Cav1.3 knockout mice. These findings argue that 5-HT2receptors couple through Gαq proteins to trigger a phospholipase Cβ/inositol trisphosphate signaling cascade resulting in the mobilization of intracellular Ca2+, activation of calcineurin, and inhibition of Cav1.2 L-type Ca2+currents. This modulation and its blockade by atypical neuroleptics could have wide-ranging effects on synaptic integration and long-term gene expression in deep-layer prefrontal pyramidal neurons.

Analysis of voltage-gated and synaptic conductances contributing to network excitability defects in the mutant mouse tottering

1994 ◽  
Vol 71 (1) ◽  
pp. 1-10 ◽  
Author(s):  
S. A. Helekar ◽  
J. L. Noebels
Keyword(s):  
Gabaa Receptor ◽  
Pyramidal Neurons ◽  
Hippocampal Slices ◽  
Channel Blockers ◽  
Gamma Aminobutyric Acid ◽  
Voltage Gated ◽  
Voltage Dependent ◽  
Prolonged Duration ◽  
Ca3 Pyramidal Neurons ◽  
The Difference

1. Intracellular current- and voltage-clamp recordings were carried out in CA3 pyramidal neurons from hippocampal slices of adult tg/tg mice and their coisogenic C57BL/6J (+/+) controls with the use of the single-electrode switch-clamp technique. The principal aim of this study was to investigate the mechanisms responsible for the tg gene-linked prolongation (mean 60%) of a giant synaptic response, the potassium-induced paroxysmal depolarizing shift (PDS) at depolarized membrane potentials (Vm -47 to -54 mV) during synchronous network bursting induced by 10 mM potassium ([K+]o). 2. To examine the role of intrinsic voltage-dependent conductances underlying the mutant PDS prolongation, neurons were voltage clamped by the use of microelectrodes filled with 100 mM QX-314 or QX-222 chloride (voltage-gated sodium channel blockers) and 2 M cesium sulphate (potassium channel blocker). The whole-cell currents active during the PDS showed a significantly prolonged duration (mean 34%) at depolarized Vms in tg/tg compared with +/+ cells, indicating that a defect in voltage-dependent conductances is unlikely to completely account for the mutant phenotype. 3. Bath application of 40 microM (DL)-2-aminophosphonovalerate (DL-APV) produced a 30% reduction in PDS duration in both genotypes but failed to significantly alter the tg gene-linked prolongation compared with the wild type. These data indicate that the mutant PDS abnormality does not result from a selective increase of the N-methyl-D-aspartate (NMDA) receptor-mediated excitatory synaptic component. 4. Blockade of gamma-aminobutyric acid-A (GABAA) transmission with picrotoxin (50 microM) or bicuculline (1–5 microM) completely eliminated the difference in PDS duration between the genotypes. Furthermore, although both GABAA receptor antagonists increased the mean PDS duration in +/+ neurons, they did not significantly alter it in tg/tg neurons. These findings are consistent with a reduction in GABAA receptor-mediated synaptic inhibition during bursting in the tg CA3 hippocampal network. 5. To test this hypothesis, bursting CA3 pyramidal neurons were loaded intracellularly with chloride by the use of KCl-filled microelectrodes to examine the effect of reversing the hyperpolarizing chloride-dependent GABAA receptor-mediated inhibitory postsynaptic component of the PDS. Chloride loading prolonged PDS duration in both genotypes, but the increase was greater in +/+ than in tg/tg neurons, indicating that a smaller GABAA inhibitory postsynaptic potential (IPSP) component was reversed in the mutant.(ABSTRACT TRUNCATED AT 400 WORDS)

Localization and trafficking of cardiac voltage-gated potassium channels

2007 ◽  
Vol 35 (5) ◽  
pp. 1069-1073 ◽  
Author(s):  
D.F. Steele ◽  
A. Dehghani Zadeh ◽  
M.E. Loewen ◽  
D. Fedida
Keyword(s):  
Potassium Channels ◽  
Molecular Motors ◽  
Action Potentials ◽  
Voltage Gated ◽  
Anchoring Proteins

The proper trafficking and localization of cardiac potassium channels is profoundly important to the regulation of the regionally distinct action potentials across the myocardium. These processes are only beginning to be unravelled and involve modulators of channel synthesis and assembly, post-translational processing, various molecular motors and an increasing number of modifying enzymes and molecular anchors. The roles of anchoring proteins, molecular motors and kinases are explored and recent findings on channel internalization and trafficking are presented.

Dynamic regulation of the voltage-gated Kv2.1 potassium channel by multisite phosphorylation

2007 ◽  
Vol 35 (5) ◽  
pp. 1064-1068 ◽  
Author(s):  
D.P. Mohapatra ◽  
K.-S. Park ◽  
J.S. Trimmer
Keyword(s):  
Neuronal Excitability ◽  
Critical Role ◽  
Functional Characterization ◽  
K Channel ◽  
Delayed Rectifier ◽  
Dynamic Regulation ◽  
Voltage Gated ◽  
Voltage Dependent ◽  
Specific Regulation

Voltage-gated K+ channels are key regulators of neuronal excitability. The Kv2.1 voltage-gated K+ channel is the major delayed rectifier K+ channel expressed in most central neurons, where it exists as a highly phosphorylated protein. Kv2.1 plays a critical role in homoeostatic regulation of intrinsic neuronal excitability through its activity- and calcineurin-dependent dephosphorylation. Here, we review studies leading to the identification and functional characterization of in vivo Kv2.1 phosphorylation sites, a subset of which contribute to graded modulation of voltage-dependent gating. These findings show that distinct developmental-, cell- and state-specific regulation of phosphorylation at specific sites confers a diversity of functions on Kv2.1 that is critical to its role as a regulator of intrinsic neuronal excitability.

scholarly journals Molecular determinants of afferent sensitization in a rat model of cystitis with urothelial barrier dysfunction

2019 ◽  
Vol 122 (3) ◽  
pp. 1136-1146 ◽  
Author(s):  
Nicolas Montalbetti ◽  
James G. Rooney ◽  
Anna C. Rued ◽  
Marcelo D. Carattino
Keyword(s):  
Interstitial Cystitis ◽  
Sensory Neurons ◽  
Rat Model ◽  
Pain Syndrome ◽  
Bladder Pain Syndrome ◽  
Repetitive Firing ◽  
Delayed Rectifier ◽  
Mrna Levels ◽  
Bladder Pain ◽  
Voltage Gated

The internal surface of the urinary bladder is covered by the urothelium, a stratified epithelium that forms an impermeable barrier to urinary solutes. Increased urothelial permeability is thought to contribute to symptom generation in several forms of cystitis by sensitizing bladder afferents. In this report we investigate the physiological mechanisms that mediate bladder afferent hyperexcitability in a rat model of cystitis induced by overexpression in the urothelium of claudin-2 (Cldn2), a tight junction-associated protein upregulated in bladder biopsies from patients with interstitial cystitis/bladder pain syndrome. Patch-clamp studies showed that overexpression of Cldn2 in the urothelium sensitizes a population of isolectin GS-IB4-negative [IB4(−)] bladder sensory neurons with tetrodotoxin-sensitive (TTX-S) action potentials. Gene expression analysis revealed a significant increase in mRNA levels of the delayed-rectifier voltage-gated K+ channel (Kv)2.2 and the accessory subunit Kv9.1 in this population of bladder sensory neurons. Consistent with this finding, Kv2/Kv9.1 channel activity was greater in IB4(−) bladder sensory neurons from rats overexpressing Cldn2 in the urothelium than in control counterparts. Likewise, current density of TTX-S voltage-gated Na+ (Nav) channels was greater in sensitized neurons than in control counterparts. Significantly, guangxitoxin-1E (GxTX-1E), a selective blocker of Kv2 channels, blunted the repetitive firing of sensitized IB4(−) sensory neurons. In summary, our studies indicate that an increase in the activity of TTX-S Nav and Kv2/Kv9.1 channels mediates repetitive firing of sensitized bladder sensory neurons in rats with increased urothelial permeability. NEW & NOTEWORTHY Hyperexcitability of sensitized bladder sensory neurons in a rat model of interstitial cystitis/bladder pain syndrome (IC/BPS) results from increased activity of tetrodotoxin-sensitive voltage-gated Na+ and delayed-rectifier voltage-gated K+ (Kv)2/Kv9.1 channels. Of major significance, our studies indicate that Kv2/Kv9.1 channels play a major role in symptom generation in this model of IC/BPS by maintaining the sustained firing of the sensitized bladder sensory neurons.

Specificity in the Interaction of HVA Ca2+ Channel Types With Ca2+-Dependent AHPs and Firing Behavior in Neocortical Pyramidal Neurons

1998 ◽  
Vol 79 (5) ◽  
pp. 2522-2534 ◽  
Author(s):  
Juan Carlos Pineda ◽  
Robert S. Waters ◽  
Robert C. Foehring
Keyword(s):  
Brain Slice ◽  
Pyramidal Neurons ◽  
Repetitive Firing ◽  
Channel Blockers ◽  
Firing Behavior ◽  
Inward Currents ◽  
Functional Consequences ◽  
P Type ◽  
Brain Slice Preparation ◽  
Neocortical Pyramidal Neurons

Pineda, Juan Carlos, Roberts S. Waters, and Robert C. Foehring. Specificity in the interaction of HVA Ca2+ channel types with Ca2+-dependent AHPs and firing behavior in neocortical pyramidal neurons. J. Neurophysiol. 79: 2522–2534, 1998. Intracellular recordings and organic and inorganic Ca2+ channel blockers were used in a neocortical brain slice preparation to test whether high-voltage–activated (HVA) Ca2+ channels are differentially coupled to Ca2+-dependent afterhyperpolarizations (AHPs) in sensorimotor neocortical pyramidal neurons. For the most part, spike repolarization was not Ca2+ dependent in these cells, although the final phase of repolarization (after the fast AHP) was sensitive to block of N-type current. Between 30 and 60% of the medium afterhyperpolarization (mAHP) and between ∼80 and 90% of the slow AHP (sAHP) were Ca2+ dependent. Based on the effects of specific organic Ca2+ channel blockers (dihydropyridines, ω-conotoxin GVIA, ω-agatoxin IVA, and ω-conotoxin MVIIC), the sAHP is coupled to N-, P-, and Q-type currents. P-type currents were coupled to the mAHP. L-type current was not involved in the generation of either AHP but (with other HVA currents) contributes to the inward currents that regulate interspike intervals during repetitive firing. These data suggest different functional consequences for modulation of Ca2+ current subtypes.

scholarly journals Ca2+-activated KCa3.1 potassium channels contribute to the slow afterhyperpolarization in L5 neocortical pyramidal neurons

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
M. V. Roshchin ◽  
V. N. Ierusalimsky ◽  
P. M. Balaban ◽  
E. S. Nikitin
Keyword(s):  
Potassium Channels ◽  
Pyramidal Neurons ◽  
Neocortical Pyramidal Neurons
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