scholarly journals Midazolam’s Effects on Delayed-Rectifier K+ Current and Intermediate-Conductance Ca2+-Activated K+ Channel in Jurkat T-lymphocytes

2021 ◽  
Vol 22 (13) ◽  
pp. 7198
Author(s):  
Ning-Ping Foo ◽  
Yu-Fan Liu ◽  
Ping-Ching Wu ◽  
Chung-Hsi Hsing ◽  
Bu-Miin Huang ◽  
...  
Keyword(s):  
T Lymphocytes ◽  
Current Density ◽  
Cytokine Expression ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Inactivation Curve ◽  
Human T Lymphocytes ◽  
Concentration Time ◽  
State Dependent ◽  
K Current

Midazolam (MDZ) could affect lymphocyte immune functions. However, the influence of MDZ on cell’s K+ currents has never been investigated. Thus, in the present study, the effects of MDZ on Jurkat T lymphocytes were studied using the patch-clamp technique. Results showed that MDZ suppressed the amplitude of delayed-rectifier K+ current (IK(DR)) in concentration-, time-, and state-dependent manners. The IC50 for MDZ-mediated reduction of IK(DR) density was 5.87 μM. Increasing MDZ concentration raised the rate of current-density inactivation and its inhibitory action on IK(DR) density was estimated with a dissociation constant of 5.14 μM. In addition, the inactivation curve of IK(DR) associated with MDZ was shifted to a hyperpolarized potential with no change on the slope factor. MDZ-induced inhibition of IK(DR) was not reversed by flumazenil. In addition, the activity of intermediate-conductance Ca2+-activated K+ (IKCa) channels was suppressed by MDZ. Furthermore, inhibition by MDZ on both IK(DR) and IKCa-channel activity appeared to be independent from GABAA receptors and affected immune-regulating cytokine expression in LPS/PMA-treated human T lymphocytes. In conclusion, MDZ suppressed current density of IK(DR) in concentration-, time-, and state-dependent manners in Jurkat T-lymphocytes and affected immune-regulating cytokine expression in LPS/PMA-treated human T lymphocytes.

scholarly journals Characterization of the Inhibitory Effect of Gastrodigenin and Gastrodin on M-type K+ Currents in Pituitary Cells and Hippocampal Neurons

2019 ◽  
Vol 21 (1) ◽  
pp. 117 ◽  
Author(s):  
Chih-Sheng Yang ◽  
Ming-Chi Lai ◽  
Ping-Yen Liu ◽  
Yi-Ching Lo ◽  
Chin-Wei Huang ◽  
...  
Keyword(s):  
Current Density ◽  
Time Course ◽  
Gh3 Cells ◽  
Delayed Rectifier ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Activation Time ◽  
Patch Clamp Technique ◽  
Type K ◽  
K Current

Gastrodigenin (HBA) and gastrodin (GAS) are phenolic ingredients found in Gastrodia elata Blume (GEB), a traditional Chinese herbal medicine. These compounds have been previously used to treat cognitive dysfunction, convulsion, and dizziness. However, at present, there is no available information regarding their potential ionic effects in electrically excitable cells. In the current study, the possible effects of HBA and GAS on different ionic currents in pituitary GH3 cells and hippocampal mHippoE-14 neurons were investigated using the patch-clamp technique. The addition of HBA or GAS resulted in the differential inhibition of the M-type K+ current (IK(M)) density in a concentration-dependent manner in GH3 cells. HBA resulted in a slowing of the activation time course of IK(M), while GAS elevated it. HBA also mildly suppressed the density of erg-mediated or the delayed-rectifier K+ current in GH3 cells. Neither GAS nor HBA (10 µM) modified the voltage-gated Na+ current density, although they suppressed the L-type Ca2+ current density at the same concentration. In hippocampal mHippoE-14 neurons, HBA was effective at inhibiting IK(M) density as well as slowing the activation time course. Taken together, the present study provided the first evidence that HBA or GAS could act on cellular mechanisms, and could therefore potentially have a functional influence in various neurologic disorders.

scholarly journals Actions of FTY720 (Fingolimod), a Sphingosine-1-Phosphate Receptor Modulator, on Delayed-Rectifier K+ Current and Intermediate-Conductance Ca2+-Activated K+ Channel in Jurkat T-Lymphocytes

Molecules ◽  
2020 ◽  
Vol 25 (19) ◽  
pp. 4525
Author(s):  
Wei-Ting Chang ◽  
Ping-Yen Liu ◽  
Sheng-Nan Wu
Keyword(s):  
T Lymphocytes ◽  
Immune Cells ◽  
K Channel ◽  
Delayed Rectifier ◽  
Inactivation Kinetics ◽  
Dependent Manner ◽  
Inactivation Curve ◽  
K Channels ◽  
Sphingosine 1 Phosphate ◽  
K Current

FTY720 (fingolimod), a modulator of sphingosine-1-phosphate receptors, is known to produce the immunomodulatory actions and to be beneficial for treating the relapsing multiple sclerosis. However, whether it exerts any effects on membrane ion currents in immune cells remains largely unknown. Herein, the effects of FTY720 on ionic currents in Jurkat T-lymphocytes were investigated. Cell exposure to FTY720 suppressed the amplitude of delayed-rectifier K+ current (IK(DR)) in a time- and concentration-dependent manner with an IC50 value of 1.51 μM. Increasing the FTY720 concentration not only decreased the IK(DR) amplitude but also accelerated the inactivation time course of the current. By using the minimal reaction scheme, the effect of FTY720 on IK(DR) inactivation was estimated with a dissociation constant of 3.14 μM. FTY720 also shifted the inactivation curve of IK(DR) to a hyperpolarized potential with no change in the slope factor, and recovery from IK(DR) became slow during the exposure to this compound. Cumulative inactivation for IK(DR) in response to repetitive depolarizations was enhanced in the presence of FTY720. In SEW2871-treated cells, FTY720-induced inhibition of IK(DR) was attenuated. This compound also exerted a stimulatory action on the activity of intermediate-conductance Ca2+-activated K+ channels in Jurkat T-lymphocytes. However, in NSC-34 neuronal cells, FTY720 did not modify the inactivation kinetics of KV3.1-encoded IK(DR), although it suppressed IK(DR) amplitude in these cells. Collectively, the perturbations by FTY720 on different types of K+ channels may contribute to the functional activities of immune cells, if similar findings appear in vivo.

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.

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.

Isolated bovine retinal pigment epithelial cells express delayed rectifier type and M-type K+ currents

1997 ◽  
Vol 273 (3) ◽  
pp. C790-C803 ◽  
Author(s):  
M. Takahira ◽  
B. A. Hughes
Keyword(s):  
Retinal Pigment Epithelial ◽  
Retinal Pigment ◽  
Retinal Pigment Epithelial Cells ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Rpe Cells ◽  
Pigment Epithelial ◽  
Type K ◽  
K Current ◽  
K Currents

Outwardly rectifying K+ currents in freshly isolated bovine retinal pigment epithelial (RPE) cells were characterized using the whole cell and perforated-patch configurations of the patch-clamp technique. All cells exhibited a delayed rectifier type K+ current. This current had an activation threshold voltage of approximately -40 mV, activated with a sigmoidal trajectory, and inactivated completely over a period of several seconds. External tetraethylammonium (TEA) was an effective blocker of the delayed rectifier current [apparent dissociation constant (Kd) = 5.1 mM], but external Ba2+ was relatively ineffective. Approximately 24% of the cells also exhibited a sustained outwardly rectifying K+ current that became activated at voltages positive to approximately -80 mV. This current resembled the neuronal M-current. External Ba2+ was a potent blocker of this current (apparent Kd = 1.1 mM), but external TEA and Cs+ were relatively ineffective. These results indicate that freshly isolated bovine RPE cells express K+ currents of both the delayed rectifier and M types. The latter may contribute to the resting K+ conductances of the apical and basolateral membranes.

Blockade by lithium ions of potassium channels in rat anterior pituitary cells

1991 ◽  
Vol 261 (2) ◽  
pp. C218-C223 ◽  
Author(s):  
M. Kato ◽  
P. M. Lledo ◽  
J. D. Vincent
Keyword(s):  
Growth Hormone ◽  
Anterior Pituitary ◽  
Hormone Secretion ◽  
Male Rats ◽  
Delayed Rectifier ◽  
Pituitary Cells ◽  
Patch Clamp Technique ◽  
Anterior Pituitary Cells ◽  
K Current ◽  
K Currents

Extracellular Li+ has been known to facilitate the basal secretion of growth hormone from anterior pituitary cells and of catecholamine from chromaffin cells. In both cases, the intracellular accumulation of Li+ seems to be the prerequisite, and the presence of extracellular Ca2+ is indispensable. In this series of experiments, we examined whether Li+ blocked K+ currents by using primary cultured anterior pituitary cells from male rats. K+ currents were measured in the whole cell configuration of the patch-clamp technique. Extracellular Li+ (140 mM) suppressed both the delayed rectifier K+ current (IK) and the transient outward K+ current to 71 and 69% of control, respectively, in a reversible manner. IK elicited by a voltage step to +70 mV from holding potential of -70 mV was suppressed by 32.5 mM internal Li+ to 28% of control. Half-maximal suppression of K+ conductance by internal Li+ was 16 mM. Furthermore, Ca(2+)-channel blocker methoxyverapamil potently suppressed Li(+)-induced growth hormone secretion. From these results we propose that the blockade by Li+ of K+ channels could depolarize the cells and activate Ca2+ channels, thereby promoting the influx of Ca2+ and hormone secretion as a mechanism of Li(+)-induced hormone secretion.

An outwardly rectifying K+ current active near resting potential in human retinal pigment epithelial cells

1995 ◽  
Vol 269 (1) ◽  
pp. C179-C187 ◽  
Author(s):  
B. A. Hughes ◽  
M. Takahira ◽  
Y. Segawa
Keyword(s):  
Retinal Pigment Epithelial ◽  
Retinal Pigment ◽  
Outward Current ◽  
Resting Potential ◽  
Equilibrium Potential ◽  
Delayed Rectifier ◽  
Patch Clamp Technique ◽  
Rpe Cells ◽  
Pigment Epithelial ◽  
K Current

Currents in freshly dissociated adult human retinal pigment epithelial (RPE) cells were studied using the perforated patch-clamp technique. The zero-current potential (V0) averaged -48.9 +/- 7.7 mV (n = 50). Depolarizing voltage pulses from -70 mV evoked an outward current that activated with first-order kinetics and that did not inactivate during prolonged depolarizations. Repolarizing the membrane potential produced tail currents that reversed near the K+ equilibrium potential, indicating that the sustained outward current was carried mainly by K+. The outwardly rectifying K+ conductance (gK) had an activation threshold voltage near -60 mV and was half-maximal at -37 mV. Approximately 25% of gK was active at the average V0. The K+ current was nearly completely blocked by 2 mM Ba2+ but was relatively insensitive to 20 mM tetraethylammonium. The kinetics, voltage dependence, and blocker sensitivity of this current clearly distinguish it from delayed rectifier K+ currents previously identified in RPE cells. We conclude that the sustained outward K+ current may help establish the resting potential of the apical and/or basolateral membranes and may also participate in K+ transport across the RPE.

Monensin-Induced Increase in Intracellular Na+ Induces Changes in Na+ and Ca2+ Currents and Regulates Na+-K+ and Na+-Ca2+ Transport in Cardiomyocytes

Pharmacology ◽  
2020 ◽  
pp. 1-15
Author(s):  
Katsuharu Tsuchida ◽  
Hitomi Hirose ◽  
Sachiyo Ozawa ◽  
Haruka Ishida ◽  
Tomomi Iwatani ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Sodium Current ◽  
Pump Current ◽  
Plateau Phase ◽  
Patch Clamp Technique ◽  
Inactivation Curve ◽  
Reverse Mode ◽  
Whole Cell Patch Clamp ◽  
Intracellular Ca ◽  
K Current

<b><i>Background/Aims:</i></b> Monensin, an Na ionophore, increases intracellular Na ([Na]i). Alteration of [Na]i influences ion transport through the sarcolemmal membrane. So far, the effects of monensin on ventricular myocytes have not been examined in detail. The main objective of this study was to elucidate the mechanism via which monensin-evoked increases in [Na]i affect the membrane potential and currents in ventricular myocytes of guinea pigs. Methods: Membrane potentials and currents were measured using the whole-cell patch-clamp technique in single myocytes. The concentration of intracellular Ca ([Ca]i) was evaluated by measuring fluorescence intensity of Fluo-4. Results: Monensin (10<sup>−5</sup>M) shortened the action potential duration (APD) and reduced the amplitude of the plateau phase. In addition, monensin decreased the sodium current (I<sub>Na</sub>) and shifted the inactivation curve to the hyperpolarized direction. Moreover, it decreased the L-type calcium current (I<sub>Ca</sub>). However, this effect was attenuated by increasing the buffering capacity of [Ca]i. The Na-Ca exchange current (I<sub>Na-Ca</sub>) was activated particularly in the reverse mode. Na-K pump current (I<sub>Na-K</sub>) was also activated. Notably, the inward rectifying K current (I<sub>K1</sub>) was not affected, and the change in the delayed outward K current (I<sub>K</sub>) was not evident. Conclusion: These results suggest that the monensin-induced shortened APD and reduced amplitude of the plateau phase are primarily due to the decrease in the I<sub>Ca</sub>, the activation of the reverse mode of I<sub>Na-Ca</sub>, and the increased I<sub>Na-K</sub>, and second due to the decreased I<sub>Na</sub>. The I<sub>K</sub> and the I<sub>K1</sub> may not be associated with the abovementioned changes induced by monensin. The elevation of [Na]i can exert multiple influences on electrophysiological phenomena in cardiac myocytes.

scholarly journals The Electrophysiological Effects of Qiliqiangxin on Cardiac Ventricular Myocytes of Rats

2013 ◽  
Vol 2013 ◽  
pp. 1-4 ◽  
Author(s):  
Yidong Wei ◽  
Xiaoyu Liu ◽  
Haidong Wei ◽  
Lei Hou ◽  
Wenliang Che ◽  
...  
Keyword(s):  
Ventricular Myocytes ◽  
Sodium Current ◽  
Chinese Herb ◽  
Antiarrhythmic Therapy ◽  
Delayed Rectifier ◽  
Ca Channel ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
K Current ◽  
Cardiac Ventricular Myocytes

Qiliqiangxin, a Chinese herb, represents the affection in Ca channel function of cardiac myocytes. It is unknown whether Qiliqiangxin has an effect on Na current and K current because the pharmacological actions of this herb’s compound are very complex. We investigated the rational usage of Qiliqiangxin on cardiac ventricular myocytes of rats. Ventricular myocytes were exposed acutely to 1, 10, and 50 mg/L Qiliqiangxin, and whole cell patch-clamp technique was used to study the acute effects of Qiliqiangxin on Sodium current (INa), outward currents delayed rectifier outward K+current (IK), slowly activating delayed rectifier outward K+current (IKs), transient outward K+current (Ito), and inward rectifier K+current (IK1). Qiliqiangxin can decreaseINaby28.53%±5.98%, and its IC50was 9.2 mg/L. 10 and 50 mg/L Qiliqiangxin decreased by37.2%±6.4%and55.9%±5.5%summit current density ofIto. 10 and 50 mg/L Qiliqiangxin decreasedIKsby15.51%±4.03%and21.6%±5.6%. Qiliqiangxin represented a multifaceted pharmacological profile. The effects of Qiliqiangxin on Na and K currents of ventricular myocytes were more profitable in antiarrhythmic therapy in the clinic. We concluded that the relative efficacy of Qiliqiangxin was another choice for the existing antiarrhythmic therapy.

Magnesium shifts voltage dependence of activation of delayed rectifier I(K) in guinea pig ventricular myocytes

1997 ◽  
Vol 272 (3) ◽  
pp. H1292-H1301 ◽  
Author(s):  
B. A. Williams ◽  
G. N. Beatch
Keyword(s):  
Guinea Pig ◽  
Ventricular Myocytes ◽  
Inward Rectification ◽  
Delayed Rectifier ◽  
Maximal Effect ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
K Current ◽  
Dose Dependent Decrease ◽  
20 Nm

The sensitivity of the delayed rectifier K+ current (I(K)) to intracellular Mg2+ was investigated in guinea pig ventricular myocytes using the whole cell patch-clamp technique. An increase in free intracellular Mg2+ concentration ([Mg2+]i) led to a dose-dependent decrease in I(K) with a half-maximal effect of approximately 20 nM. Activation of I(K) was shifted toward more positive voltages on increasing [Mg2+]i, but little effect was observed on activation and deactivation kinetics. Isoproterenol increased I(K) and was partially reversible in both control and 100 nM [Mg2+]i. The antiarrhythmic drug dofetilide was used to separate I(K) into its two components, rapidly activating (I(Kr)) and slowly activating (I(Ks)). The magnitude of both components decreased to a similar extent with an increase in [Mg2+]i. As [Mg2+]i was reduced, however, the number of experiments in which the dofetilide-sensitive current I(Kr) displayed inward rectification was reduced. In contrast to results previously reported for frog myocytes, it is unlikely that Mg2+ effects on guinea pig I(K) are mediated by a protein phosphatase.

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