Effects of K+ Channel Blockers on Developing Rat Myelinated CNS Axons: Identification of Four Types of K+Channels

2002 ◽  
Vol 87 (3) ◽  
pp. 1376-1385 ◽  
Author(s):  
Jerome Devaux ◽  
Maurice Gola ◽  
Guy Jacquet ◽  
Marcel Crest
Keyword(s):  
Optic Nerve ◽  
Refractory Period ◽  
K Channel ◽  
Channel Blockers ◽  
Optic Nerves ◽  
Kv Channel ◽  
Kv Channels ◽  
Compound Action Potentials ◽  
Channel Expression ◽  
The One

Four blockers of voltage-gated potassium channels (Kv channels) were tested on the compound action potentials (CAPs) of rat optic nerves in an attempt to determine the regulation of Kv channel expression during the process of myelination. Before myelination occurred, 4-aminopyridine (4-AP) increased the amplitude, duration, and refractory period of the CAPs. On the basis of their pharmacological sensitivity, 4-AP-sensitive channels were divided in two groups, the one sensitive to kaliotoxin (KTX), dendrotoxin-I (DTX-I), and 4-AP, and the other sensitive only to 4-AP. In addition, tetraethylammonium chloride (TEA) applied alone broadened the CAPs. At the onset of myelination, DTX-I induced a more pronounced effect than KTX; this indicates that a fourth group of channels sensitive to 4-AP and DTX-I but insensitive to KTX had developed. The effects of KTX and DTX-I gradually disappeared during the period of myelination. Electron microscope findings showed that the disappearance of these effects was correlated with the ongoing process of myelination. This was confirmed by the fact that DTX-I and KTX enlarged the CAPs of demyelinated adult optic nerves. These results show that KTX- and DTX-sensitive channels are sequestrated in paranodal regions. During the process of myelination, KTX had less pronounced effects than DTX-I on demyelinated nerves, which suggests that the density of the KTX-sensitive channels decreased during this process. By contrast, 4-AP increased the amplitude, duration, and refractory period of the CAPs at all the ages tested and to a greater extent than KTX and DTX-I. The effects of TEA alone also gradually disappeared during this period. However, effects of TEA on CAPs were observed when this substance was applied after 4-AP to the adult optic nerve; this shows that TEA-sensitive channels are not masked by the myelin sheath. In conclusion, the process of myelination seems to play an important part in the regulation and setting of Kv channels in optic nerve axons.

Comparison of aldosterone- and RU-28362-induced apical Na+ and K+ conductances in rat distal colon

1994 ◽  
Vol 267 (3) ◽  
pp. G485-G493 ◽  
Author(s):  
R. B. Lomax ◽  
G. I. Sandle
Keyword(s):  
Distal Colon ◽  
Distal Segment ◽  
K Channel ◽  
Rat Colon ◽  
Na Channel ◽  
Channel Blockers ◽  
Mineralocorticoid Antagonist ◽  
Channel Expression ◽  
K Secretion ◽  
Crypt Cells

In mammalian distal colon, aldosterone induces electrogenic Na+ absorption and electrogenic K+ secretion, whereas the sole transport effect of specific glucocorticoid agonists is thought to be stimulation of electroneutral NaCl absorption. In this study, intracellular microelectrodes and Na(+)- and K(+)-channel blockers were used to compare the effects of aldosterone and RU-28362 (a specific glucocorticoid agonist) on apical Na+ and K+ conductances in surface cells and upper crypt cells in the most distal colonic segment from adrenalectomized rats. In control animals, surface cells and crypt cells were devoid of apical Na+ and K+ conductances. In aldosterone-treated animals (70 micrograms.100 g body wt-1.day-1 for 7 days), Na+ conductances were induced in 88% of surface cells but only 40% of crypt cells, and the distribution of K+ conductances was similar (82% of surface cells and 50% of crypt cells). The same dose of RU-28362 also induced Na+ conductances in 82% of surface cells and 50% of crypt cells, which tended to be smaller than those induced by aldosterone. RU-28362, in contrast to aldosterone, had no effect on apical K+ conductance in surface cells or crypt cells. Concurrent treatment with the mineralocorticoid antagonist RU-28318 (3.5 mg.100 g body wt-1.day-1 for 7 days) inhibited Na(+)-channel expression in aldosterone-treated animals but had no effect in RU-28362-treated animals. We conclude that in the most distal segment of rat colon, aldosterone acts via mineralocorticoid receptors to induce apical Na+ and K+ conductances, which are only fully expressed in the surface cell population.(ABSTRACT TRUNCATED AT 250 WORDS)

scholarly journals Scanning the Intracellular S6 Activation Gate in the Shaker K+ Channel

2002 ◽  
Vol 119 (6) ◽  
pp. 521-531 ◽  
Author(s):  
David H. Hackos ◽  
Tsg-Hui Chang ◽  
Kenton J. Swartz
Keyword(s):  
Ionic Currents ◽  
K Channel ◽  
Dependent Manner ◽  
Kv Channel ◽  
Closed State ◽  
Kv Channels ◽  
Gate Structure ◽  
Activation Gate ◽  
Voltage Dependent ◽  
Gate Region

In Kv channels, an activation gate is thought to be located near the intracellular entrance to the ion conduction pore. Although the COOH terminus of the S6 segment has been implicated in forming the gate structure, the residues positioned at the occluding part of the gate remain undetermined. We use a mutagenic scanning approach in the Shaker Kv channel, mutating each residue in the S6 gate region (T469-Y485) to alanine, tryptophan, and aspartate to identify positions that are insensitive to mutation and to find mutants that disrupt the gate. Most mutants open in a steeply voltage-dependent manner and close effectively at negative voltages, indicating that the gate structure can both support ion flux when open and prevent it when closed. We find several mutant channels where macroscopic ionic currents are either very small or undetectable, and one mutant that displays constitutive currents at negative voltages. Collective examination of the three types of substitutions support the notion that the intracellular portion of S6 forms an activation gate and identifies V478 and F481 as candidates for occlusion of the pore in the closed state.

scholarly journals Structure of a pore-blocking toxin in complex with a eukaryotic voltage-dependent K+ channel

eLife ◽  
2013 ◽  
Vol 2 ◽  
Author(s):  
Anirban Banerjee ◽  
Alice Lee ◽  
Ernest Campbell ◽  
Roderick MacKinnon
Keyword(s):  
Electron Density ◽  
Selectivity Filter ◽  
K Channel ◽  
Wild Type ◽  
Kv Channel ◽  
Pore Blocking ◽  
Kv Channels ◽  
Filter Structure ◽  
Conduction Pathway ◽  
Voltage Dependent

Pore-blocking toxins inhibit voltage-dependent K+ channels (Kv channels) by plugging the ion-conduction pathway. We have solved the crystal structure of paddle chimera, a Kv channel in complex with charybdotoxin (CTX), a pore-blocking toxin. The toxin binds to the extracellular pore entryway without producing discernable alteration of the selectivity filter structure and is oriented to project its Lys27 into the pore. The most extracellular K+ binding site (S1) is devoid of K+ electron-density when wild-type CTX is bound, but K+ density is present to some extent in a Lys27Met mutant. In crystals with Cs+ replacing K+, S1 electron-density is present even in the presence of Lys27, a finding compatible with the differential effects of Cs+ vs K+ on CTX affinity for the channel. Together, these results show that CTX binds to a K+ channel in a lock and key manner and interacts directly with conducting ions inside the selectivity filter.

scholarly journals Molecular Template for a Voltage Sensor in a Novel K+ Channel. I. Identification and Functional Characterization of KvLm, a Voltage-gated K+ Channel from Listeria monocytogenes

2006 ◽  
Vol 128 (3) ◽  
pp. 283-292 ◽  
Author(s):  
Jose S. Santos ◽  
Alicia Lundby ◽  
Cecilia Zazueta ◽  
Mauricio Montal
Keyword(s):  
Listeria Monocytogenes ◽  
Voltage Sensor ◽  
K Channel ◽  
Open Probability ◽  
Voltage Gated ◽  
Kv Channel ◽  
Kv Channels ◽  
Sensor Module ◽  
Single Channel Currents ◽  
Hallmark Feature

The fundamental principles underlying voltage sensing, a hallmark feature of electrically excitable cells, are still enigmatic and the subject of intense scrutiny and controversy. Here we show that a novel prokaryotic voltage-gated K+ (Kv) channel from Listeria monocytogenes (KvLm) embodies a rudimentary, yet robust, sensor sufficient to endow it with voltage-dependent features comparable to those of eukaryotic Kv channels. The most conspicuous feature of the KvLm sequence is the nature of the sensor components: the motif is recognizable; it appears, however, to contain only three out of eight charged residues known to be conserved in eukaryotic Kv channels and accepted to be deterministic for folding and sensing. Despite the atypical sensor sequence, flux assays of KvLm reconstituted in liposomes disclosed a channel pore that is highly selective for K+ and is blocked by conventional Kv channel blockers. Single-channel currents recorded in symmetric K+ solutions from patches of enlarged Escherichia coli (spheroplasts) expressing KvLm showed that channel open probability sharply increases with depolarization, a hallmark feature of Kv channels. The identification of a voltage sensor module in KvLm with a voltage dependence comparable to that of other eukaryotic Kv channels yet encoded by a sequence that departs significantly from the consensus sequence of a eukaryotic voltage sensor establishes a molecular blueprint of a minimal sequence for a voltage sensor.

Gene transcription of brain voltage-gated potassium channels is reversibly regulated by oxygen supply

2003 ◽  
Vol 285 (6) ◽  
pp. R1317-R1321 ◽  
Author(s):  
Howard M. Prentice ◽  
Sarah L. Milton ◽  
Daniela Scheurle ◽  
Peter L. Lutz
Keyword(s):  
Potassium Channels ◽  
Oxygen Supply ◽  
Brain Activity ◽  
Acute Hypoxia ◽  
Mrna Levels ◽  
Voltage Gated ◽  
Kv Channel ◽  
Kv Channels ◽  
Voltage Dependent ◽  
Channel Expression

Voltage-dependent potassium channels (Kv channels) are important determinants of brain electrical activity. Hypoxia may be an important modifier, because several voltage-gated K+ channels are reversibly blocked by acute hypoxia and are thought to act as oxygen sensors. Here we show, using the anoxia-tolerant turtle brain ( Trachemys scripta) as a model, that brain Kv1 channel transcription is reversibly regulated by oxygen supply. We found that in turtle brains exposed to 4-h anoxia Kv1 transcripts were reduced to 18.5% of normoxic levels. Kv1 channel mRNA levels were restored to normal within 4 h of subsequent reoxygenation. Our results provide clear evidence that brain Kv channel expression is sensitive to oxygen supply and indicate an important mechanism that matches brain activity to oxygen supply.

scholarly journals Fatty Acid and Related Potassium Kv2 Channel Blockers: Toxicity and Physiological Actions on Mosquitoes

Insects ◽  
2018 ◽  
Vol 9 (4) ◽  
pp. 155 ◽  
Author(s):  
Fabien Démares ◽  
Quentin Coquerel ◽  
Gary Richoux ◽  
Kenneth Linthicum ◽  
Jeffrey Bloomquist
Keyword(s):  
Decanoic Acid ◽  
Cellular Level ◽  
Hydroxyl Group ◽  
Channel Blockers ◽  
Synergistic Activity ◽  
Insecticidal Effect ◽  
Kv Channel ◽  
Kv Channels ◽  
Potassium Channel Blockers ◽  
First Time

Potassium channels constitute a very diverse group involved in neural signaling, neuronal activity, membrane potential maintenance, and action potential generation. Here, we tested the mammalian potassium channel blockers TRAM-34 and 5-hydroxydecanoate (5-HDC), as well as certain fatty acids (FA) that might fit in the lumen of the pore and block channel activity by obstructing K+ ion passage. Kv channel blockers could be leads for a novel pesticide type. Insecticidal activity was assessed by topical application to Anopheles gambiae adult mosquitoes, paralysis in a headless larval assay, at the cellular level with patch-clamp recordings of engineered HEK cells expressing AgKv2.1 channels, as well as central nervous system recordings from larval Drosophila melanogaster. With only one hydroxyl group difference, decanoic acid had a consistently greater effect than 5-HDC in blocking Kv channels, paralyzing larvae, and killing mosquitoes. The 11-dansylamino undecanoic acid (DAUDA) blockage of eukaryotic Kv channels is demonstrated for the first time, but it failed to kill adult mosquitoes. We synthesized alkyl esters from DAUDA and decanoic acid in an effort to improve cuticular penetration, but it had little impact upon adult toxicity. TRAM-34 and rolipram did not show activity on Kv channels nor potent insecticidal effect on adult mosquitoes. Furthermore, co-application of test compounds with permethrin did not increase mortality in adults. In conclusion, the compounds tested had modest insecticidal and synergistic activity.

KChAP/Kvβ1.2 interactions and their effects on cardiac Kv channel expression

2001 ◽  
Vol 281 (1) ◽  
pp. C290-C299 ◽  
Author(s):  
Y. A. Kuryshev ◽  
B. A. Wible ◽  
T. I. Gudz ◽  
A. N. Ramirez ◽  
A. M. Brown
Keyword(s):  
Kv Channel ◽  
Kv Channels ◽  
Cytoplasmic Proteins ◽  
Outward Currents ◽  
Different Types ◽  
Voltage Dependent ◽  
Channel Expression

KChAP and voltage-dependent K+ (Kv) β-subunits are two different types of cytoplasmic proteins that interact with Kv channels. KChAP acts as a chaperone for Kv2.1 and Kv4.3 channels. It also binds to Kv1.x channels but, with the exception of Kv1.3, does not increase Kv1.x currents. Kvβ-subunits are assembled with Kv1.x channels; they exhibit “chaperone-like” behavior and change gating properties. In addition, KChAP and Kvβ-subunits interact with each other. Here we examine the consequences of this interaction on Kv currents in Xenopusoocytes injected with different combinations of cRNAs, including Kvβ1.2, KChAP, and either Kv1.4, Kv1.5, Kv2.1, or Kv4.3. We found that KChAP attenuated the depression of Kv1.5 currents produced by Kvβ1.2, and Kvβ1.2 eliminated the increase of Kv2.1 and Kv4.3 currents produced by KChAP. Both KChAP and Kvβ1.2 are expressed in cardiomyocytes, where Kv1.5 and Kv2.1 produce sustained outward currents and Kv4.3 and Kv1.4 generate transient outward currents. Because they interact, either KChAP or Kvβ1.2 may alter both sustained and transient cardiac Kv currents. The interaction of these two different classes of modulatory proteins may constitute a novel mechanism for regulating cardiac K+ currents.

scholarly journals Molecular Template for a Voltage Sensor in a Novel K+ Channel. II. Conservation of a Eukaryotic Sensor Fold in a Prokaryotic K+ Channel

2006 ◽  
Vol 128 (3) ◽  
pp. 293-300 ◽  
Author(s):  
Alicia Lundby ◽  
Jose S. Santos ◽  
Cecilia Zazueta ◽  
Mauricio Montal
Keyword(s):  
Consensus Sequence ◽  
Voltage Sensor ◽  
K Channel ◽  
Functional Coupling ◽  
Voltage Sensitivity ◽  
Conserved Residues ◽  
Kv Channel ◽  
Kv Channels ◽  
Sensor Module ◽  
The Impact

KvLm, a novel bacterial depolarization-activated K+ (Kv) channel isolated from the genome of Listeria monocytogenes, contains a voltage sensor module whose sequence deviates considerably from the consensus sequence of a Kv channel sensor in that only three out of eight conserved charged positions are present. Surprisingly, KvLm exhibits the steep dependence of the open channel probability on membrane potential that is characteristic of eukaryotic Kv channels whose sensor sequence approximates the consensus. Here we asked if the KvLm sensor shared a similar fold to that of Shaker, the archetypal eukaryotic Kv channel, by examining if interactions between conserved residues in Shaker known to mediate sensor biogenesis and function were conserved in KvLm. To this end, each of the five non-conserved residues in the KvLm sensor were mutated to their Shaker-like charged residues, and the impact of these mutations on the voltage dependence of activation was assayed by current recordings from excised membrane patches of Escherichia coli spheroplasts expressing the KvLm mutants. Conservation of pairwise interactions was investigated by comparison of the effect of single mutations to the impact of double mutations presumed to restore wild-type fold and voltage sensitivity. We observed significant functional coupling between sites known to interact in Shaker Kv channels, supporting the notion that the KvLm sensor largely retains the fold of its eukaryotic homologue.

scholarly journals Opening the Shaker K+ channel with hanatoxin

2013 ◽  
Vol 141 (2) ◽  
pp. 203-216 ◽  
Author(s):  
Mirela Milescu ◽  
Hwa C. Lee ◽  
Chan Hyung Bae ◽  
Jae Il Kim ◽  
Kenton J. Swartz
Keyword(s):  
K Channel ◽  
Voltage Sensors ◽  
Channel Interaction ◽  
Kv Channel ◽  
Kv Channels ◽  
Structural Details ◽  
In The Wild ◽  
Protein Toxins ◽  
Electrical Signaling ◽  
Voltage Relationship

Voltage-activated ion channels open and close in response to changes in membrane voltage, a property that is fundamental to the roles of these channels in electrical signaling. Protein toxins from venomous organisms commonly target the S1–S4 voltage-sensing domains in these channels and modify their gating properties. Studies on the interaction of hanatoxin with the Kv2.1 channel show that this tarantula toxin interacts with the S1–S4 domain and inhibits opening by stabilizing a closed state. Here we investigated the interaction of hanatoxin with the Shaker Kv channel, a voltage-activated channel that has been extensively studied with biophysical approaches. In contrast to what is observed in the Kv2.1 channel, we find that hanatoxin shifts the conductance–voltage relation to negative voltages, making it easier to open the channel with membrane depolarization. Although these actions of the toxin are subtle in the wild-type channel, strengthening the toxin–channel interaction with mutations in the S3b helix of the S1-S4 domain enhances toxin affinity and causes large shifts in the conductance–voltage relationship. Using a range of previously characterized mutants of the Shaker Kv channel, we find that hanatoxin stabilizes an activated conformation of the voltage sensors, in addition to promoting opening through an effect on the final opening transition. Chimeras in which S3b–S4 paddle motifs are transferred between Kv2.1 and Shaker Kv channels, as well as experiments with the related tarantula toxin GxTx-1E, lead us to conclude that the actions of tarantula toxins are not simply a product of where they bind to the channel, but that fine structural details of the toxin–channel interface determine whether a toxin is an inhibitor or opener.

scholarly journals Molecular Template for a Voltage Sensor in a Novel K+ Channel. III. Functional Reconstitution of a Sensorless Pore Module from a Prokaryotic Kv Channel

2008 ◽  
Vol 132 (6) ◽  
pp. 651-666 ◽  
Author(s):  
Jose S. Santos ◽  
Sergey M. Grigoriev ◽  
Mauricio Montal
Keyword(s):  
Lipid Bilayers ◽  
Single Channel ◽  
Functional Module ◽  
Ion Selectivity ◽  
Ionic Currents ◽  
K Channel ◽  
Voltage Sensing ◽  
Kv Channel ◽  
Kv Channels ◽  
Conduction Properties

KvLm is a prokaryotic voltage-gated K+ (Kv) channel from Listeria monocytogenes. The sequence of the voltage-sensing module (transmembrane segments S1-S4) of KvLm is atypical in that it contains only three of the eight conserved charged residues known to be deterministic for voltage sensing in eukaryotic Kv's. In contrast, the pore module (PM), including the S4-S5 linker and cytoplasmic tail (linker-S5-P-S6-C-terminus) of KvLm, is highly conserved. Here, the full-length (FL)-KvLm and the KvLm-PM only proteins were expressed, purified, and reconstituted into giant liposomes. The properties of the reconstituted FL-KvLm mirror well the characteristics of the heterologously expressed channel in Escherichia coli spheroplasts: a right-shifted voltage of activation, micromolar tetrabutylammonium-blocking affinity, and a single-channel conductance comparable to that of eukaryotic Kv's. Conversely, ionic currents through the PM recapitulate both the conductance and blocking properties of the FL-KvLm, yet the KvLm-PM exhibits only rudimentary voltage dependence. Given that the KvLm-PM displays many of the conduction properties of FL-KvLm and of other eukaryotic Kv's, including strict ion selectivity, we conclude that self-assembly of the PM subunits in lipid bilayers, in the absence of the voltage-sensing module, generates a conductive oligomer akin to that of the native KvLm, and that the structural independence of voltage sensing and PMs observed in eukaryotic Kv channels was initially implemented by nature in the design of prokaryotic Kv channels. Collectively, the results indicate that this robust functional module will prove valuable as a molecular template for coupling new sensors and to elucidate PM residue–specific contributions to Kv conduction properties.

Sign in / Sign up

Export Citation Format

Share Document