Voltage-activated whole-cell K+ currents in lamina cells of the desert locust schistocerca gregaria

1999 ◽  
Vol 202 (14) ◽  
pp. 1939-1951 ◽  
Author(s):  
C. Benkenstein ◽  
M. Schmidt ◽  
M. Gewecke
Keyword(s):  
Voltage Dependence ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Whole Cell ◽  
Group I ◽  
Outward Currents ◽  
K Current ◽  
Group Ii ◽  
I Cells ◽  
In Cells

Voltage-dependent outward currents were studied in freshly dissociated somata of locust lamina cells. These currents were recorded in 142 somata using the whole-cell patch-clamp technique. By measuring the reversal potential at altered external [K+] and by replacing internal K+ with Cs+, we determined that the outward currents were carried by K+. The outward currents consist of a transient A-type K+ current (KA) and a delayed-rectifier-like K+ current (KD). Amongst the cells studied, we observed two distinct groups of cells. The most obvious difference between the two groups is that in group I cells the total outward current is dominated by KA (KA/KD=12.5), whereas in group II cells KA makes a smaller contribution (KA/KD=2.1). Furthermore, in cells of group I, the KA current shows a steeper voltage-dependence of activation, where VG50 is −29.9 mV and s is 11.9 (N=22), and inactivation, where VI50 is −84.5 mV and s is −6.3 (N=18), compared with the KA current in cells of group II: VG50=−7.9 mV; s=26.6 (N=36) and VI50=−68.4 mV; s=−7.5 (N=21) (VG50 is the voltage at which the whole-cell conductance G is half-maximally activated, VI50 is the voltage of half-maximal inactivation and s is the slope of the voltage-dependence). The transient KA current in group I cells decayed mono-exponentially. The decay of the KA current in group II cells was fitted with a double-exponential curve and was significantly faster than in group I cells. In contrast to the large differences in KA currents, the KD currents appeared to be quite similar in the two groups of cells.

Transient potassium currents in avian sensory neurons

1990 ◽  
Vol 63 (4) ◽  
pp. 725-737 ◽  
Author(s):  
S. K. Florio ◽  
C. D. Westbrook ◽  
M. R. Vasko ◽  
R. J. Bauer ◽  
J. L. Kenyon
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Potassium Currents ◽  
Delayed Rectifier ◽  
Transient Outward Current ◽  
Single Channels ◽  
Patch Clamp Technique ◽  
Small Component ◽  
Whole Cell ◽  
Outward Currents

1. We used the patch-clamp technique to study voltage-activated transient potassium currents in freshly dispersed and cultured chick dorsal root ganglion (DRG) cells. Whole-cell and cell-attached patch currents were recorded under conditions appropriate for recording potassium currents. 2. In whole-cell experiments, 100-ms depolarizations from normal resting potentials (-50 to -70 mV) elicited sustained outward currents that inactivated over a time scale of seconds. We attribute this behavior to a component of delayed rectifier current. After conditioning hyperpolarizations to potentials negative to -80 mV, depolarizations elicited transient outward current components that inactivated with time constants in the range of 8-26 ms. We attribute this behavior to a transient outward current component. 3. Conditioning hyperpolarizations increased the rate of activation of the net outward current implying that the removal of inactivation of the transient outward current allows it to contribute to early outward current during depolarizations from negative potentials. 4. Transient current was more prominent on the day the cells were dispersed and decreased with time in culture. 5. In cell-attached patches, single channels mediating outward currents were observed that were inactive at resting potentials but were active transiently during depolarizations to potentials positive to -30 mV. The probability of channels being open increased rapidly (peaking within approximately 6 ms) and then declined with a time constant in the range of 13-30 ms. With sodium as the main extracellular cation, single-channel conductances ranged from 18 to 32 pS. With potassium as the main extracellular cation, the single-channel conductance was approximately 43 pS, and the channel current reversed near 0 mV, as expected for a potassium current. 6. We conclude that the transient potassium channels mediate the component of transient outward current seen in the whole-cell experiments. This current is a relatively small component of the net current during depolarizations from normal resting potentials, but it can contribute significant outward current early in depolarizations from hyperpolarized potentials.

Spontaneous transient outward currents and delayed rectifier K+ current: effects of hypoxia

1998 ◽  
Vol 275 (1) ◽  
pp. L145-L154 ◽  
Author(s):  
C. Vandier ◽  
M. Delpech ◽  
P. Bonnet
Keyword(s):  
Steady State ◽  
Outward Current ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Outward Currents ◽  
K Current ◽  
The Mean ◽  
Patch Configuration ◽  
Spontaneous Transient Outward Currents ◽  
Dependent Mechanism

Single smooth muscle cells of rabbit intrapulmonary artery were voltage clamped using the perforated-patch configuration of the patch-clamp technique. We observed spontaneous transient outward currents (STOCs) and a steady-state outward current. Because STOCs were tetraethylammonium sensitive and activated by Ca2+ influx, they were believed to represent activation of Ca2+-activated K+ channels. The steady-state outward current, which was sensitive to 4-aminopyridine, was the delayed rectifier K+ current. In cells voltage clamped at 0 mV, we found that STOCs were not randomly distributed in amplitude but were composed of multiples of 1.57 ± 0.56 pA/pF. The mean frequency of STOCs was 5.51 ± 3.49 Hz. Ryanodine (10 μM), caffeine (5 mM), thapsigargin (200 nM), and hypoxia [Formula: see text] = 10 mmHg) decreased STOCs. The effect of hypoxia on STOCs was partially reversible only if the experiment was conducted in the presence of thapsigargin. Hypoxia and thapsigargin decrease steady-state outward current. Thapsigargin and removal of external Ca2+abolished the effect of hypoxia, suggesting that hypoxia decreases steady-state outward current by a Ca2+-dependent mechanism.

Ion channels in rabbit cultured fibroblasts

1986 ◽  
Vol 227 (1246) ◽  
pp. 1-16 ◽  
Keyword(s):  
Calcium Concentration ◽  
Voltage Dependence ◽  
Single Channel ◽  
Outward Current ◽  
Patch Clamp Technique ◽  
Cultured Fibroblasts ◽  
Whole Cell ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
High Conductance

Large outward currents are recorded with the whole-cell patch-clamp technique on depolarization of rabbit cultured fibroblasts. Our findings suggest that these outward currents consist of two voltage-dependent components, one of which also depends on cytoplasmic calcium concentration. Total replacement of external Cl - by the large anion ascorbate does not affect the amplitude of the currents, indicating that both components must be carried by K + . Consistent with these findings with whole-cell currents, in single channel recordings from fibroblasts we found that most patches contain high-conductance potassium-selective channels whose activation depends on both membrane potential and the calcium concentration at the cytoplasmic surface of the membrane. In a smaller number of patches, a second population of high-conductance calcium-independent potassium channels is observed having different voltage-dependence. The calcium- and voltage-dependence suggest that these two channels correspond with the two components of outward current seen in the whole-cell recordings. The single channel conductance of both channels in symmetrical KCl (150 mM) is 260-270 pS. Both channels are highly selective for K + over both Na + and Cl - . The conductance of the channels when outward current is carried by Rb + is considerably smaller than when it is carried by K + . Some evidence is adduced to support the hypothesis that these potassium channel populations may be involved in the control of cell proliferation.

Nitric oxide mediates outward potassium currents in opossum esophageal circular smooth muscle

1996 ◽  
Vol 270 (6) ◽  
pp. G932-G938 ◽  
Author(s):  
J. Jury ◽  
K. R. Boev ◽  
E. E. Daniel
Keyword(s):  
Nitric Oxide ◽  
Smooth Muscle ◽  
Circular Muscle ◽  
Outward Current ◽  
Equilibrium Potential ◽  
Patch Clamp Technique ◽  
Pipette Solution ◽  
Whole Cell ◽  
Circular Smooth Muscle ◽  
Outward Currents

Single smooth muscle cells from the opossum body circular muscle were isolated and whole cell currents were characterized by the whole cell patch-clamp technique. When the cells were held at -50 mV and depolarized to 70 mV in 20-mV increments, initial small inactivating inward currents were evoked (-30 to 30 mV) followed by larger sustained outward currents. Depolarization from a holding potential of -90 mV evoked an initial fast inactivating outward current sensitive to 4-aminopyridine but not to high levels of ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA). The outward currents reversed near K+ equilibrium potential and were abolished when KCl was replaced by CsCl in the pipette solution. The sustained outward current was inhibited by quinine and cesium. High EGTA in the pipette solution reduced but did not abolish the sustained outward currents, suggesting that both Ca(2+)-dependent and -independent currents were evoked. The nitric oxide (NO)-releasing agents Sin-1 and sodium nitroprusside increased outward K+ currents. High levels of EGTA in the pipette solution abolished the increase in outward current induced by Sin-1. The presence of cyclopiazonic acid, an inhibitor of the sarcoplasmic reticulum (SR) Ca2+ pump, blocked the effects of NO-releasing agents. We conclude that NO release activates K+ outward currents in opossum esophagus circular muscle, which may depend on Ca2+ release from the SR stores.

scholarly journals Activation of Slo2.1 channels by niflumic acid

2010 ◽  
Vol 135 (3) ◽  
pp. 275-295 ◽  
Author(s):  
Li Dai ◽  
Vivek Garg ◽  
Michael C. Sanguinetti
Keyword(s):  
Voltage Dependence ◽  
Reversal Potential ◽  
Niflumic Acid ◽  
Flufenamic Acid ◽  
Channel Activation ◽  
Outward Currents ◽  
Transmembrane Voltage ◽  
High K ◽  
Charged Residues ◽  
K Current

Slo2.1 channels conduct an outwardly rectifying K+ current when activated by high [Na+]i. Here, we show that gating of these channels can also be activated by fenamates such as niflumic acid (NFA), even in the absence of intracellular Na+. In Xenopus oocytes injected with <10 ng cRNA, heterologously expressed human Slo2.1 current was negligible, but rapidly activated by extracellular application of NFA (EC50 = 2.1 mM) or flufenamic acid (EC50 = 1.4 mM). Slo2.1 channels activated by 1 mM NFA exhibited weak voltage dependence. In high [K+]e, the conductance–voltage (G-V) relationship had a V1/2 of +95 mV and an effective valence, z, of 0.48 e. Higher concentrations of NFA shifted V1/2 to more negative potentials (EC50 = 2.1 mM) and increased the minimum value of G/Gmax (EC50 = 2.4 mM); at 6 mM NFA, Slo2.1 channel activation was voltage independent. In contrast, V1/2 of the G-V relationship was shifted to more positive potentials when [K+]e was elevated from 1 to 300 mM (EC50 = 21.2 mM). The slope conductance measured at the reversal potential exhibited the same [K+]e dependency (EC50 = 23.5 mM). Conductance was also [Na+]e dependent. Outward currents were reduced when Na+ was replaced with choline or mannitol, but unaffected by substitution with Rb+ or Li+. Neutralization of charged residues in the S1–S4 domains did not appreciably alter the voltage dependence of Slo2.1 activation. Thus, the weak voltage dependence of Slo2.1 channel activation is independent of charged residues in the S1–S4 segments. In contrast, mutation of R190 located in the adjacent S4–S5 linker to a neutral (Ala or Gln) or acidic (Glu) residue induced constitutive channel activity that was reduced by high [K+]e. Collectively, these findings indicate that Slo2.1 channel gating is modulated by [K+]e and [Na+]e, and that NFA uncouples channel activation from its modulation by transmembrane voltage and intracellular Na+.

scholarly journals Modulation of membrane currents by cyclic AMP in cleavage-arrested Drosophila neurons.

1996 ◽  
Vol 199 (3) ◽  
pp. 537-548
Author(s):  
W B Alshuaib ◽  
L Byerly
Keyword(s):  
Cyclic Amp ◽  
Membrane Currents ◽  
K Channel ◽  
Neuronal Membrane ◽  
Patch Clamp Technique ◽  
Large Variability ◽  
Whole Cell ◽  
Intracellular Environment ◽  
K Current ◽  
Channel Currents

A number of Drosophila learning mutants have defective intracellular second-messenger systems. In an effort to develop techniques that will allow direct measurement of the effects of these mutations on whole-cell neuronal membrane currents, the perforated-patch whole-cell (PPWC) technique has been applied to cleavage-arrested cultured embryonic Drosophila neurons. This technique permits the measurement of membrane currents without disturbing the intracellular environment. As a result of the maintenance of the intracellular environment, Drosophila neuron currents are found to be much more stable than when measured using the conventional whole-cell (CWC) patch-clamp technique. Ca2+ channel currents, which typically 'wash out' within a few minutes of the beginning of CWC recording, are stable for the duration of the seal (tens of minutes) when measured using the PPWC technique. Since the learning mutations dunce and rutabaga disrupt cyclic AMP signalling, the action of externally applied dibutyryl cyclic AMP (db-cAMP) and theophylline on Ca2+ and K+ channel currents were studied. db-cAMP and theophylline enhanced the Ba2+ current, carried by Ca2+ channels, but had no effect on the K+ current in the cleavage-arrested neurons. However, the large variability and reduction in density of Ba2+ and K+ currents raise questions about the suitability of using these cleavage-arrested cells as models for Drosophila neurons.

Outward currents in normal and hypertrophied feline ventricular myocytes

1989 ◽  
Vol 256 (5) ◽  
pp. H1450-H1461 ◽  
Author(s):  
R. B. Kleiman ◽  
S. R. Houser
Keyword(s):  
Time Course ◽  
Ventricular Myocytes ◽  
Pressure Overload ◽  
Negative Slope ◽  
Inward Rectification ◽  
Delayed Rectifier ◽  
Outward Currents ◽  
K Current ◽  
Prolongation Of Action Potential ◽  
The Right

The properties of the inward rectifier K current (IK1) and the delayed rectifier K current (IK) were studied in single feline myocytes isolated from the right ventricle of normal cats and cats with experimentally induced right ventricular hypertrophy (RVH). IK1 demonstrated time-dependent decay during hyperpolarizations and showed inward rectification with a prominent negative-slope region between -30 and -10 mV. Both IK1 and IK was carried primarily by K ions. The activation of IK during depolarizations followed a monoexponential time course, whereas the deactivation of IK tail currents was either mono- or biexponential depending on the repolarization potential. IK showed marked rectification at positive potentials. A comparison of these currents in normal and hypertrophy myocytes revealed that in RVH the magnitude of IK1 is increased, whereas the magnitude of IK is decreased. IK showed steeper rectification, had slower activation, and had more rapid deactivation in RVH. These abnormalities of the IK may contribute to the prolongation of action potential duration, which characterizes pressure-overload cardiac hypertrophy.

scholarly journals A time- and voltage-dependent K+ current in single cardiac cells from bullfrog atrium.

1986 ◽  
Vol 88 (6) ◽  
pp. 777-798 ◽  
Author(s):  
J R Hume ◽  
W Giles ◽  
K Robinson ◽  
E F Shibata ◽  
R D Nathan ◽  
...  
Keyword(s):  
Time Course ◽  
Voltage Dependence ◽  
Outward Current ◽  
Cardiac Cells ◽  
Delayed Rectifier ◽  
Mechanical Dispersion ◽  
Atrial Cells ◽  
Voltage Dependent ◽  
K Current ◽  
Kinetics Of

Individual myocytes were isolated from bullfrog atrium by enzymatic and mechanical dispersion, and a one-microelectrode voltage clamp was used to record the slow outward K+ currents. In normal [K+]o (2.5 mM), the slow outward current tails reverse between -95 and -100 mV. This finding, and the observed 51-mV shift of Erev/10-fold change in [K+]o, strongly suggest that the "delayed rectifier" in bullfrog atrial cells is a K+ current. This current, IK, plays an important role in initiating repolarization, and it is distinct from the quasi-instantaneous, inwardly rectifying background current, IK. In atrial cells, IK does not exhibit inactivation, and very long depolarizing clamp steps (20 s) can be applied without producing extracellular K+ accumulation. The possibility of [K+]o accumulation contributing to these slow outward current changes was assessed by (a) comparing reversal potentials measured after short (2 s) and very long (15 s) activating prepulses, and (b) studying the kinetics of IK at various holding potentials and after systematically altering [K+]o. In the absence of [K+]o accumulation, the steady state activation curve (n infinity) and fully activated current-voltage (I-V) relation can be obtained directly. The threshold of the n infinity curve is near -50 mV, and it approaches a maximum at +20 mV; the half-activation point is approximately -16 mV. The fully activated I-V curve of IK is approximately linear in the range -40 to +30 mV. Semilog plots of the current tails show that each tail is a single-exponential function, which suggests that only one Hodgkin-Huxley conductance underlies this slow outward current. Quantitative analysis of the time course of onset of IK and of the corresponding envelope of tails demonstrate that the activation variable, n, must be raised to the second power to fit the sigmoid onset accurately. The voltage dependence of the kinetics of IK was studied by recording and curve-fitting activating and deactivating (tail) currents. The resulting 1/tau n curve is U-shaped and somewhat asymmetric; IK exhibits strong voltage dependence in the diastolic range of potentials. Changes in the [Ca2+]o in the superfusing Ringer's, and/or addition of La3+ to block the transmembrane Ca2+ current, show that the time course and magnitude of IK are not significantly modulated by transmembrane Ca2+ movements, i.e., by ICa. These experimentally measured voltage- and time-dependent descriptors of IK strongly suggest an important functional role for IK in atrial tissue: it initiates repolarization and can be an important determinant of rate-induced changes in action potential duration.

scholarly journals Voltage-dependent conductances in Limulus ventral photoreceptors.

1982 ◽  
Vol 79 (2) ◽  
pp. 187-209 ◽  
Author(s):  
J E Lisman ◽  
G L Fain ◽  
P M O'Day
Keyword(s):  
Outward Current ◽  
Delayed Rectifier ◽  
Molluscan Neurons ◽  
Inward Current ◽  
Transient Component ◽  
Outward Currents ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
A Current

The voltage-dependent conductances of Limulus ventral photoreceptors have been investigated using a voltage-clamp technique. Depolarization in the dark induces inward and outward currents. The inward current is reduced by removing Na+ or Ca2+ and is abolished by removing both ions. These results suggest that both Na+ and Ca2+ carry voltage-dependent inward current. Inward current is insensitive to tetrodotoxin but is blocked by external Ni2+. The outward current has a large transient component that is followed by a smaller maintained component. Intracellular tetraethylammonium preferentially reduces the maintained component, and extracellular 4-amino pyridine preferentially reduces the transient component. Neither component is strongly affected by removal of extracellular Ca2+ or by intracellular injection of EGTA. It is concluded that the photoreceptors contain at least three separate voltage-dependent conductances: 1) a conductance giving rise to inward currents; 2) a delayed rectifier giving rise to maintained outward K+ current; and 3) a rapidly inactivating K+ conductance similar to the A current of molluscan neurons.

scholarly journals Mechanisms of IhERG/IKr Modulation by α1-Adrenoceptors in HEK293 Cells and Cardiac Myocytes

2016 ◽  
Vol 40 (6) ◽  
pp. 1261-1273 ◽  
Author(s):  
Janire Urrutia ◽  
Aintzane Alday ◽  
Mónica Gallego ◽  
L. Layse Malagueta-Vieira ◽  
Ivan Arael Aréchiga-Figueroa ◽  
...  
Keyword(s):  
Ventricular Fibrillation ◽  
Cardiac Myocytes ◽  
Torsades De Pointes ◽  
Hek293 Cells ◽  
Herg Channel ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
K Current ◽  
Herg Channels ◽  
Intracellular Pathway

Background: The rapid delayed rectifier K+ current (IKr), carried by the hERG protein, is one of the main repolarising currents in the human heart and a reduction of this current increases the risk of ventricular fibrillation. α1-adrenoceptors (α1-AR) activation reduces IKr but, despite the clear relationship between an increase in the sympathetic tone and arrhythmias, the mechanisms underlying the α1-AR regulation of the hERG channel are controversial. Thus, we aimed to investigate the mechanisms by which α1-AR stimulation regulates IKr. Methods: α1-adrenoceptors, hERG channels, auxiliary subunits minK and MIRP1, the non PIP2-interacting mutant D-hERG (with a deletion of the 883-894 amino acids) in the C-terminal and the non PKC-phosphorylable mutant N-terminal truncated-hERG (NTK-hERG) were transfected in HEK293 cells. Cell membranes were extracted by centrifugation and the different proteins were visualized by Western blot. Potassium currents were recorded by the patch-clamp technique. IKr was recorded in isolated feline cardiac myocytes. Results: Activation of the α1-AR reduces the amplitude of IhERG and IKr through a positive shift in the activation half voltage, which reduces the channel availability at physiological membrane potentials. The intracellular pathway connecting the α1-AR to the hERG channel in HEK293 cells includes activation of the Gαq protein, PLC activation and PIP2 hydrolysis, activation of PKC and direct phosphorylation of the hERG channel N-terminal. The PKC-mediated IKr channel phosphorylation and subsequent IKr reduction after α1-AR stimulation was corroborated in feline cardiac myocytes. Conclusions: These findings clarify the link between sympathetic nervous system hyperactivity and IKr reduction, one of the best characterized causes of torsades de pointes and ventricular fibrillation.

Sign in / Sign up

Export Citation Format

Share Document