The voltage-dependent K+ channel (Kv1.5) cloned from rabbit heart and facilitation of inactivation of the delayed rectifier current by the rat β subunit

FEBS Letters ◽  
1995 ◽  
Vol 372 (1) ◽  
pp. 20-24 ◽  
Author(s):  
Yoshiteru Sasaki ◽  
Kuniaki Ishii ◽  
Kazuo Nunoki ◽  
Toshio Yamagishi ◽  
Norio Taira
Keyword(s):  
Rabbit Heart ◽  
K Channel ◽  
Delayed Rectifier ◽  
Β Subunit ◽  
Delayed Rectifier Current ◽  
Voltage Dependent

Complexity of the outward K+ current of the rat megakaryocyte

1997 ◽  
Vol 272 (5) ◽  
pp. C1525-C1531 ◽  
Author(s):  
E. Romero ◽  
R. Sullivan
Keyword(s):  
K Channel ◽  
Delayed Rectifier ◽  
Channel Blockers ◽  
Excitable Cells ◽  
Electrophysiological Properties ◽  
Relative Contribution ◽  
Delayed Rectifier Current ◽  
Dependent Inactivation ◽  
Voltage Dependent ◽  
K Current

Megakaryocytes isolated from rat bone marrow express a voltage-dependent, outward K+ current with complex kinetics of activation and inactivation. We found that this current could be separated into at least two components based on differential responses to K+ channel blockers. One component, which exhibited features of the "transient" or "A-type" K+ current of excitable cells, was more strongly blocked by 4-aminopyridine (4-AP) than by tetrabutylammonium (TBA). This current, which we designated as "4-AP-sensitive" current, activated rapidly at potentials more positive than -40 mV and subsequently underwent rapid voltage-dependent inactivation. A separate current that activated slowly was blocked much more effectively by TBA than by 4-AP. This "TBA-sensitive" component, which resembled a typical delayed rectifier current, was much more resistant to voltage-dependent inactivation. The relative contribution of each of these components varied from cell to cell. The effect of charybdotoxin was similar to that of 4-AP. Our data indicate that the voltage-dependent K+ current of resting megakaryocytes is more complex than heretofore believed and support the emerging concept that megakaryocytes possess intricate electrophysiological properties.

Members of the Kv1 and Kv2 Voltage-Dependent K+ Channel Families Regulate Insulin Secretion

2001 ◽  
Vol 15 (8) ◽  
pp. 1423-1435 ◽  
Author(s):  
Patrick E. MacDonald ◽  
Xiao Fang Ha ◽  
Jing Wang ◽  
Simon R. Smukler ◽  
Anthony M. Sun ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
K Channel ◽  
Delayed Rectifier ◽  
Β Cells ◽  
Rat Islets ◽  
Kv Channels ◽  
Delayed Rectifier Current ◽  
Voltage Dependent ◽  
Glucose Stimulated Insulin Secretion ◽  
Insulinoma Cells

Abstract In pancreatic β-cells, voltage-dependent K+ (Kv) channels are potential mediators of repolarization, closure of Ca2+ channels, and limitation of insulin secretion. The specific Kv channels expressed in β-cells and their contribution to the delayed rectifier current and regulation of insulin secretion in these cells are unclear. High-level protein expression and mRNA transcripts for Kv1.4, 1.6, and 2.1 were detected in rat islets and insulinoma cells. Inhibition of these channels with tetraethylammonium decreased IDR by approximately 85% and enhanced glucose-stimulated insulin secretion by 2- to 4-fold. Adenovirus-mediated expression of a C-terminal truncated Kv2.1 subunit, specifically eliminating Kv2 family currents, reduced delayed rectifier currents in these cells by 60–70% and enhanced glucose-stimulated insulin secretion from rat islets by 60%. Expression of a C-terminal truncated Kv1.4 subunit, abolishing Kv1 channel family currents, reduced delayed rectifier currents by approximately 25% and enhanced glucose-stimulated insulin secretion from rat islets by 40%. This study establishes that Kv2 and 1 channel homologs mediate the majority of repolarizing delayed rectifier current in rat β-cells and that antagonism of Kv2.1 may prove to be a novel glucose-dependent therapeutic treatment for type 2 diabetes.

Distinct domains of the voltage-gated K+ channel Kvβ1.3 β-subunit affect voltage-dependent gating

1998 ◽  
Vol 274 (6) ◽  
pp. C1485-C1495 ◽  
Author(s):  
Victor N. Uebele ◽  
Sarah K. England ◽  
Daniel J. Gallagher ◽  
Dirk J. Snyders ◽  
Paul B. Bennett ◽  
...  
Keyword(s):  
Amino Acids ◽  
Time Constant ◽  
K Channel ◽  
Delayed Rectifier ◽  
Slow Inactivation ◽  
Β Subunit ◽  
Mediated Effects ◽  
Voltage Dependent ◽  
Partial Inactivation ◽  
Internal Pore

The Kvβ1.3 subunit confers a voltage-dependent, partial inactivation (time constant = 5.76 ± 0.14 ms at +50 mV), an enhanced slow inactivation, a hyperpolarizing shift in the activation midpoint, and an increase in the deactivation time constant of the Kv1.5 delayed rectifier. Removal of the first 10 amino acids from Kvβ1.3 eliminated the effects on fast and slow inactivation but not the voltage shift in activation. Addition of the first 87 amino acids of Kvβ1.3 to the amino terminus of Kv1.5 reconstituted fast and slow inactivation without altering the midpoint of activation. Although an internal pore mutation that alters quinidine block (V512A) did not affect Kvβ1.3-mediated inactivation, a mutation of the external mouth of the pore (R485Y) increased the extent of fast inactivation while preventing the enhancement of slow inactivation. These data suggest that 1) Kvβ1.3-mediated effects involve at least two distinct domains of this β-subunit, 2) inactivation involves open channel block that is allosterically linked to the external pore, and 3) the Kvβ1.3-induced shift in the activation midpoint is functionally distinct from inactivation.

Differential Oxidative Modulation of Voltage-Dependent K+ Currents in Rat Hippocampal Neurons

2002 ◽  
Vol 87 (6) ◽  
pp. 2990-2995 ◽  
Author(s):  
Wolfgang Müller ◽  
Katrin Bittner
Keyword(s):  
Hydrogen Peroxide ◽  
Hippocampal Neurons ◽  
Immune Defense ◽  
Delayed Rectifier ◽  
Delayed Rectifier Current ◽  
Cell Recording ◽  
Voltage Dependent ◽  
Steady State Inactivation ◽  
K Currents ◽  
Stimulation Of

Oxidative stress is enhanced by [Ca2+]i-dependent stimulation of phospholipases and mitochondria and has been implicated in immune defense, ischemia, and excitotoxicity. Using whole cell recording from hippocampal neurons, we show that arachidonic acid (AA) and hydrogen peroxide (H2O2) both reduce the transient K+ current I A by −54 and −68%, respectively, and shift steady-state inactivation by −10 and −15 mV, respectively. While AA was effective at an extracellular concentration of 1 μM and an intracellular concentration of 1 pM, extracellular H2O2 was equally effective only at a concentration >800 μM (0.0027%). In contrast to AA, H2O2 decreased the slope of activation and increased the slope of inactivation of I A and reduced the sustained delayed rectifier current I K(V) by 22% and shifted its activation by −9 mV. Intracellular application of the antioxidant glutathione (GSH, 2–5 mM) blocked all effects of AA and the reduction of I A by H2O2. In contrast, intracellular GSH enhanced reduction of I K(V) by H2O2. Decrease of the slope of activation and increase of the slope of inactivation of I A by hydrogen peroxide was blocked and reversed to a decrease, respectively, by intracellular application of GSH. Intracellular GSH did not prevent H2O2 to shift inactivation and activation of I A and activation of I K(V) to more negative potentials. We conclude, that AA and H2O2modulate voltage-activated K currents differentially by oxidation of GSH accessible intracellular and GSH inaccessible extracellular K+-channel domains, thereby presumably affecting neuronal information processing and oxidative damage.

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.

Characterization and functional consequences of delayed rectifier current transient in ventricular repolarization

2000 ◽  
Vol 278 (3) ◽  
pp. H806-H817 ◽  
Author(s):  
Gary A. Gintant
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Inward Rectifier ◽  
Ventricular Repolarization ◽  
Delayed Rectifier ◽  
Voltage Range ◽  
Delayed Rectifier Current ◽  
Recovery From Inactivation ◽  
Voltage Dependent

Although inactivation of the rapidly activating delayed rectifier current ( I Kr) limits outward current on depolarization, the role of I Kr (and recovery from inactivation) during repolarization is uncertain. To characterize I Krduring ventricular repolarization (and compare with the inward rectifier current, I K1), voltage-clamp waveforms simulating the action potential were applied to canine ventricular, atrial, and Purkinje myocytes. In ventricular myocytes, I Kr was minimal at plateau potentials but transiently increased during repolarizing ramps. The I Kr transient was unaffected by repolarization rate and maximal after 150-ms depolarizations (+25 mV). Action potential clamps revealed the I Kr transient terminating the plateau. Although peak I Kr transient density was relatively uniform among myocytes, potentials characterizing the peak transients were widely dispersed. In contrast, peak inward rectifier current ( I K1) density during repolarization was dispersed, whereas potentials characterizing I K1 defined a narrower (more negative) voltage range. In summary, rapidly activating I Kr provides a delayed voltage-dependent (and functionally time-independent) outward transient during ventricular repolarization, consistent with rapid recovery from inactivation. The heterogeneous voltage dependence of I Kr provides a novel means for modulating the contribution of this current during repolarization.

Testosterone-induced relaxation of rat aorta is androgen structure specific and involves K+ channel activation

2001 ◽  
Vol 91 (6) ◽  
pp. 2742-2750 ◽  
Author(s):  
Andrew Q. Ding ◽  
John N. Stallone
Keyword(s):  
Rank Order ◽  
Specific Effect ◽  
Rat Aorta ◽  
Isometric Tension ◽  
K Channel ◽  
Delayed Rectifier ◽  
Sprague Dawley ◽  
Voltage Dependent ◽  
Rat Thoracic Aorta ◽  
Lower Permeability

Recent studies have established that testosterone (Tes) produces acute (nongenomic) vasorelaxation. This study examined the structural specificity of Tes-induced vasorelaxation and the role of vascular smooth muscle (VSM) K+ channels in rat thoracic aorta. Aortic rings from male Sprague-Dawley rats with (Endo+) and without endothelium (Endo−) were prepared for isometric tension recording. In Endo− aortas precontracted with phenylephrine, 5–300 μM Tes produced dose-dependent relaxation from 10 μM (4 ± 1%) to 300 μM (100 ± 1%). In paired Endo+ and Endo− aortas, Tes-induced vasorelaxation was slightly but significantly greater in Endo+ aortas (at 5–150 μM Tes); sensitivity (EC50) of the aorta to Tes was reduced by nearly one-half in Endo− vessels. Based on the sensitivity (EC50) of Endo− aortas, Tes, the active metabolite 5α-dihydrotestosterone, the major excretory metabolites androsterone and etiocholanolone, the nonpolar esters Tes-enanthate and Tes-hemisuccinate (THS), and THS conjugates to BSA (THS-BSA) exhibited relative potencies for vasorelaxation dramatically different from androgen receptor-mediated effects observed in reproductive tissues, with a rank order of THS-BSA > Tes > androsterone = THS = etiocholanolone > dihydrotestosterone ≫ Tes-enanthate. Pretreatment of aortas with 5 mM 4-aminopyridine attenuated Tes-induced vasorelaxation by an average of 44 ± 2% (25–300 μM Tes). In contrast, pretreatment of aortas with other K+ channel inhibitors had no effect. These data reveal that Tes-induced vasorelaxation is a structurally specific effect of the androgen molecule, which is enhanced in more polar analogs that have a lower permeability to the VSM cell membrane, and that the effect of Tes involves activation of K+ efflux through K+channels in VSM, perhaps via the voltage-dependent (delayed-rectifier) K+ channel.

scholarly journals Permeation of Na+ through a delayed rectifier K+ channel in chick dorsal root ganglion neurons.

1994 ◽  
Vol 104 (4) ◽  
pp. 747-771 ◽  
Author(s):  
M J Callahan ◽  
S J Korn
Keyword(s):  
Dorsal Root Ganglion ◽  
Binding Site ◽  
Dorsal Root ◽  
Reversal Potential ◽  
Dorsal Root Ganglion Neurons ◽  
K Channel ◽  
Delayed Rectifier ◽  
Cation Binding Site ◽  
Voltage Dependent ◽  
Ganglion Neurons

In whole-cell patch clamp recordings from chick dorsal root ganglion neurons, removal of intracellular K+ resulted in the appearance of a large, voltage-dependent inward tail current (Icat). Icat was not Ca2+ dependent and was not blocked by Cd2+, but was blocked by Ba2+. The reversal potential for Icat shifted with the Nernst potential for [Na+]. The channel responsible for Icat had a cation permeability sequence of Na+ > Li+ > TMA+ > NMG+ (PX/PNa = 1:0.33:0.1:0) and was impermeable to Cl-. Addition of high intracellular concentrations of K+, Cs+, or Rb+ prevented the occurrence of Icat. Inhibition of Icat by intracellular K+ was voltage dependent, with an IC50 that ranged from 3.0-8.9 mM at membrane potentials between -50 and -110 mV. This voltage-dependent shift in IC50 (e-fold per 52 mV) is consistent with a single cation binding site approximately 50% of the distance into the membrane field. Icat displayed anomolous mole fraction behavior with respect to Na+ and K+; Icat was inhibited by 5 mM extracellular K+ in the presence of 160 mM Na+ and potentiated by equimolar substitution of 80 mM K+ for Na+. The percent inhibition produced by both extracellular and intracellular K+ at 5 mM was identical. Reversal potential measurements revealed that K+ was 65-105 times more permeant than Na+ through the Icat channel. Icat exhibited the same voltage and time dependence of inactivation, the same voltage dependence of activation, and the same macroscopic conductance as the delayed rectifier K+ current in these neurons. We conclude that Icat is a Na+ current that passes through a delayed rectifier K+ channel when intracellular K+ is reduced to below 30 mM. At intracellular K+ concentrations between 1 and 30 mM, PK/PNa remained constant while the conductance at -50 mV varied from 80 to 0% of maximum. These data suggest that the high selectivity of these channels for K+ over Na+ is due to the inability of Na+ to compete with K+ for an intracellular binding site, rather than a barrier that excludes Na+ from entry into the channel or a barrier such as a selectivity filter that prevents Na+ ions from passing through the channel.

Cloning and characterization of a Kv1.5 delayed rectifier K+ channel from vascular and visceral smooth muscles

1994 ◽  
Vol 267 (5) ◽  
pp. C1231-C1238 ◽  
Author(s):  
K. E. Overturf ◽  
S. N. Russell ◽  
A. Carl ◽  
F. Vogalis ◽  
P. J. Hart ◽  
...  
Keyword(s):  
Single Channel ◽  
Smooth Muscles ◽  
Functional Expression ◽  
K Channel ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
Transmembrane Segments ◽  
Delayed Rectifier Current ◽  
Current Voltage Curve ◽  
High Level

We have cloned and characterized the expression of a Kv1.5 K+ channel (cKv1.5) from canine colonic smooth muscle. The amino acid sequence displayed a high level of identity to other K+ channels of the Kv1.5 class in the core region between transmembrane segments S1-S6; however, identity decreased to between 74 and 82% in the NH2 and COOH terminal segments, suggesting that cKv1.5 is a distinct isoform of the Kv1.5 class. Functional expression of cKv1.5 in oocytes demonstrated a channel highly selective for K+, which activates in a voltage-dependent manner on depolarization to membrane potentials positive to -40 mV. At room temperature the channel showed fast activation (time to half of peak current, 5.5 ms) and slow inactivation that was incomplete after 20-s depolarizations. Single channel analysis of the channel expressed in oocytes displayed a linear current-voltage curve and had a slope conductance of 9.8 +/- 1.1 pS. Northern blot analysis demonstrated differential expression of cKv1.5 in smooth muscles of the gastrointestinal tract and abundant expression in several vascular smooth muscles. We propose that cKv1.5 represents a component of the delayed rectifier current in both vascular and visceral smooth muscles.

Characterization of macroscopic outward currents of canine colonic myocytes

1989 ◽  
Vol 257 (3) ◽  
pp. C461-C469 ◽  
Author(s):  
W. C. Cole ◽  
K. M. Sanders
Keyword(s):  
Outward Current ◽  
Cell Voltage ◽  
Muscle Cells ◽  
Time Dependent ◽  
Delayed Rectifier ◽  
Delayed Rectifier Current ◽  
Outward Currents ◽  
Voltage Dependent ◽  
K Current ◽  
Time Courses

Outward currents of colonic smooth muscle cells were characterized by the whole cell voltage-clamp method. Four components of outward current were identified: a time-independent and three time-dependent components. The time-dependent current showed strong outward rectification positive to -25 mV and was blocked by tetraethylammonium. The time-dependent components were separated on the basis of their time courses, voltage dependence, and pharmacological sensitivities. They are as follows. 1) A Ca2+-activated K current sensitive to external Ca2+ and Ca2+ influx was blocked by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (0.1 X 10(-3) M) and nifedipine (1 X 10(-6) and was increased by elevated Ca2+ (8 X 10(-6) M) and BAY K 8644 (1 X 10(-6) M). 2) A "delayed rectifier" current was observed that decayed slowly with time and showed no voltage-dependent inactivation. 3) Spontaneous transient outward currents that were blocked by ryanodine (2 X 10(-6) M) were also recorded. The possible contributions of these currents to the electrical activity of colonic muscle cells in situ are discussed. Ca2+-activated K current may contribute a significant conductance to the repolarizing phase of electrical slow waves.

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