scholarly journals Evidence for the Inhibition by Temozolomide, an Imidazotetrazine Family Alkylator, of Intermediate-Conductance Ca2+-Activated K+ Channels in Glioma Cells

2016 ◽  
Vol 38 (5) ◽  
pp. 1727-1742 ◽  
Author(s):  
Poh-Shiow Yeh ◽  
Shyh-Jong Wu ◽  
Te-Yu Hung ◽  
Yan-Ming Huang ◽  
Chia-Wei Hsu ◽  
...  
Keyword(s):  
Single Channel ◽  
Slow Component ◽  
Glioma Cells ◽  
Ionic Currents ◽  
Inhibitory Effect ◽  
Significant Prolongation ◽  
Voltage Dependent ◽  
Current Clamp Mode ◽  
U373 Cells ◽  
K Currents

Background: Temozolomide (TMZ), an oral alkylator of the imidazotetrazine family, is used to treat glioma. Whether this drug has any ionic effects in glioma cells remains largely unclear. Methods: With the aid of patch-clamp technology, we investigated the effects of TMZ on the ionic currents in U373 glioma cells. The mRNA expression of KCNN4 (KCa3.1) in U373 glioma cells and TMZ's effect on K+ currents in these KCNN4 siRNA-transfected U373 cells were investigated. Results: In whole-cell recordings, TMZ decreased the amplitude of voltage-dependent K+ currents (IK) in U373 cells. TMZ-induced IK inhibition was reversed by ionomycin or 1-ethyl-2-benzimidazolinone (1-EBIO). In cell-attached configuration, TMZ concentration-dependently reduced the activity of intermediate-conductance Ca2+-activated K+ (IKCa) channels with an IC50 value of 9.2 µM. Chlorzoxazone or 1-EBIO counteracted the TMZ-induced inhibition of IKCa channels. Although TMZ was unable to modify single-channel conductance, its inhibition of IKCa channels was weakly voltage-dependent and accompanied by a significant prolongation in the slow component of mean closed time. However, neitherlarge-conductance Ca2+-activated (BKCa) nor inwardly rectifying K+ (Kir) channels were affected by TMZ. In current-clamp mode, TMZ depolarized the cell membrane and 1-EBIO reversed TMZ-induced depolarization. TMZ had no effect on IK in KCNN4 siRNA-transfected U373 cells. Conclusion: In addition to the DNA damage it does, its inhibitory effect on IKCa channels accompanied by membrane depolarization could be an important mechanism underlying TMZ-induced antineoplastic actions.

Effects of cytochrome P-450 inhibitors on ionic currents in isolated rat type I carotid body cells

1996 ◽  
Vol 271 (1) ◽  
pp. C85-C92 ◽  
Author(s):  
C. J. Hatton ◽  
C. Peers
Keyword(s):  
Carotid Body ◽  
Single Channel ◽  
Ionic Currents ◽  
K Channel ◽  
Type I ◽  
Type I Cells ◽  
Channel Inhibition ◽  
Cytochrome P 450 ◽  
I Cells ◽  
K Currents

Hypoxic chemoreception in the carotid body involves selective inhibition of K+ channels in type I cells. We have investigated whether cytochrome P-450 may act as an O2 sensor coupling hypoxia to K+ channel inhibition, by investigating the actions of P-450 inhibitors to modulate channel activity (recorded using patch-clamp techniques) in type I cells isolated from 8-to 12-day-old rat pups. The imidazole antimycotic P-450 inhibitors miconazole and clotrimazole (1-10 microM) inhibited the Ca(2+)-activated (KCa) and voltage-gated K+ (Kv) currents in isolated type I cells. Single-channel recordings indicated that the KCa channels could be inhibited directly by miconazole. Miconazole also irreversibly inhibited Ca2+ channel currents. By contrast, acute application of the suicide substrate P-450 inhibitor, 1-aminobenzotriazole (1-ABT; 3 mM) was without effect on K+ or Ca2+ currents. Hypoxia (16-23 mmHg) reversibly inhibited K+ currents and prevented the inhibitory actions of miconazole. Furthermore, the inhibitory actions of miconazole could be partially reversed by hypoxia. Pretreatment of cells for 60 min with 3 mM 1-ABT substantially reduced the inhibitory actions of hypoxia on K+ currents. Our results indicate that imidazole antimycotic P-450 inhibitors can directly and nonselectively inhibit ionic channels in type I cells but, more importantly, provide evidence to suggest that hypoxic inhibition of K+ currents in type I cells is mediated in part at least by cytochrome P-450.

Excitability Increase Induced by β-Adrenergic Receptor-Mediated Activation of Hyperpolarization-Activated Cation Channels in Rat Cerebellar Basket Cells

2000 ◽  
Vol 84 (4) ◽  
pp. 2026-2034 ◽  
Author(s):  
Fumihito Saitow ◽  
Shiro Konishi
Keyword(s):  
Preceding Paper ◽  
Input Resistance ◽  
Ionic Currents ◽  
Synaptic Activity ◽  
Basket Cells ◽  
Camp Analogue ◽  
Voltage Dependent ◽  
Current Clamp Mode ◽  
Old Rats ◽  
Whole Cell Recordings

In the preceding paper, we showed that norepinephrine (NE) enhances the spontaneous spike firings in cerebellar interneurons, basket cells (BCs), resulting in an increase in the frequency of BC-spike-triggered inhibitory postsynaptic currents (IPSCs) in Purkinje cells (PCs), and that the effects of NE on GABAergic BCs are mediated by β2-adrenergic receptors. This study aimed to further examine the ionic mechanism underlying the β-adrenoceptor-mediated facilitation of GABAergic transmission at the BC-PC synapses. Using cerebellar slices obtained from 15- to 21-day-old rats and whole cell recordings, we investigated ionic currents in the BCs and the effects of the β-agonist isoproterenol (ISP) as well as forskolin on the BC excitability. Hyperpolarizing voltage steps from a holding potential of −50 mV elicited a hyperpolarization-activated inward current, I h, in the BC. This current exhibited voltage-dependent activation that was accelerated by strong hyperpolarization, displaying two time constants, 84 ± 6 and 310 ± 40 ms, at −100 mV, and was inhibited by 20 μM ZD7288. ISP and forskolin, both at 20 μM, enhanced I h by shifting the activation curve by 5.9 and 9.3 mV toward positive voltages, respectively. Under the current-clamp mode, ISP produced a depolarization of 7 ± 3 mV in BCs and reduced their input resistance to 74 ± 6%. ISP and a cAMP analogue, Rp-cAMP-S, increased the frequency of spontaneous spikes recorded from BCs using the cell-attached mode. The I h inhibitor ZD7288 decreased the BC spike frequency and abolished the ISP-induced increase in spike discharges. The results suggest that NE depolarizes the BCs through β-adrenoceptor-mediated cAMP formation linking it to activation of I h, which is, at least in part, involved in noradrenergic afferent-mediated facilitation of GABAergic synaptic activity at BC-PC connections in the rat cerebellum.

scholarly journals Depressive Effectiveness of Vigabatrin (y-Vinyl-GABA), an Antiepileptic Drug, in Intermediate-conductance Calcium-Activated Potassium Channels in Human Glioma Cells

2021 ◽  
Author(s):  
Te-Yu Hung ◽  
Huai-Ying Ingrid Huang ◽  
Sheng-Nan Wu ◽  
Chin-Wei Huang
Keyword(s):  
Antiepileptic Drug ◽  
Glioma Cells ◽  
Ionic Currents ◽  
Ionic Channels ◽  
Underlying Mechanism ◽  
Inhibitory Effect ◽  
Human Glioma ◽  
Human Glioma Cells ◽  
Calcium Activated Potassium Channels ◽  
Inwardly Rectifying

Abstract Background: Vigabatrin (VGB) is an approved non-traditional antiepileptic drug that has been revealed to have potential for treating brain tumors; however, its effect on ionic channels in glioma cells remains largely unclear. Methods: With the aid of patch-clamp technology, we investigated the effects of VGB on various ionic currents in the glioblastoma multiforme cell line 13-06-MG. Results: In cell-attached configuration, VGB concentration-dependently reduced the activity of intermediate-conductance Ca2+-activated K+ (IKCa) channels, while DCEBIO (5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one) counteracted the VGB-induced inhibition of IKCa channels. However, the activity of neither large-conductance Ca2+-activated (BKCa) nor inwardly rectifying K+ (KIR) channels were affected by the presence of VGB in human 13-06-MG cells. However, in the continued presence of VGB, the addition of GAL-021 or BaCl2 effectively suppressed BKCa and KIR channels. Conclusions: The inhibitory effect of VGB on IKCa channels demonstrated in the current study could be an important underlying mechanism of VGB-induced antineoplastic (e.g., anti-glioma) actions.

Somatostatin increases voltage-dependent potassium currents in rat somatotrophs

1990 ◽  
Vol 259 (6) ◽  
pp. C854-C861 ◽  
Author(s):  
C. Chen ◽  
J. Zhang ◽  
J. D. Vincent ◽  
J. M. Israel
Keyword(s):  
Growth Hormone ◽  
Cell Voltage ◽  
Inhibitory Effect ◽  
Delayed Rectifier ◽  
Hormone Release ◽  
Growth Hormone Release ◽  
Voltage Dependent ◽  
Inward Currents ◽  
K Current ◽  
K Currents

To study the modulatory effects of somatostatin on membrane K+ currents, whole cell voltage-clamp recordings were performed on identified rat somatotrophs in primary culture. In the presence of Co2+ (2 mM) and tetrodotoxin (1 microM) in the bath solution to block Ca2+ and Na+ inward currents, two types of voltage-activated K+ currents were identified on the basis of their kinetics and pharmacology. First, a delayed rectifier K+ current (IK) had a threshold of -20 mV, did not decay during voltage steps lasting 300 ms, and was markedly attenuated by extracellular application of tetraethylammonium (TEA, 10 mM). Second, a transient outward K+ current (IA) was activated at -40 mV (from a holding potential of -80 mV) and persisted despite the presence of TEA. This IA was blocked by 4-aminopyridine (2 mM). Somatostatin (10 nM) increased IK by 75% and IA by 45% without obvious effects on steady-state voltage dependency of activation or inactivation, and these effects were reversible. This increase in K+ currents may contribute in part to the inhibitory effect of somatostatin on growth hormone release.

scholarly journals Depressive Effectiveness of Vigabatrin (y-Vinyl-GABA), an Antiepileptic Drug, in Intermediate-conductance Calcium-Activated Potassium Channels in Human Glioma Cells

2020 ◽  
Author(s):  
Te-Yu Hung ◽  
Huai-Ying Ingrid Huang ◽  
Sheng-Nan Wu ◽  
Chin-Wei Huang
Keyword(s):  
Antiepileptic Drug ◽  
Glioma Cells ◽  
Ionic Currents ◽  
Underlying Mechanism ◽  
Inhibitory Effect ◽  
Human Glioma Cells ◽  
Subsequent Application ◽  
Calcium Activated Potassium Channels ◽  
Inwardly Rectifying ◽  
Ionic Effects

Abstract Background Vigabatrin (VGB, y-vinyl-GABA) is an approved non-traditional antiepileptic drug that has been revealed to have the therapeutic propensity for brain tumors; however, its ionic effects in glioma cells remain unclear to a large extent. Methods With the aid of patch-clamp technology, we investigated the effects of VGB on various ionic currents in the glioblastoma multiforme cell line 13-06-MG. Results In cell-attached configuration, addition of VGB concentration-dependently lessened the activity of intermediate-conductance Ca2+-activated K+ (IKCa) channels, while subsequent application of DCEBIO (5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one) thwarted the VGB-induced inhibition of IKCa channels. Neither the activity of large-conductance Ca2+-activated (BKCa) nor that of inwardly rectifying K+ (KIR) channels was adjusted by the presence of VGB in human 13-06-MG cells. However, in the continued presence of VGB, the addition of GAL-021 or BaCl2 effectively suppressed BKCa and KIR channels. Conclusion The inhibitory effect of VGB on IKCa channels demonstrated in the current study could be an unidentified but important underlying mechanism of VGB-induced antineoplastic (e.g., anti-glioma) actions.

scholarly journals Voltage-dependent ionic currents in taste receptor cells of the larval tiger salamander.

1990 ◽  
Vol 96 (4) ◽  
pp. 809-834 ◽  
Author(s):  
K Sugimoto ◽  
J H Teeter
Keyword(s):  
Single Channel ◽  
Outward Current ◽  
Tiger Salamander ◽  
Inward Current ◽  
Receptor Cells ◽  
Outward Currents ◽  
Taste Cells ◽  
Voltage Dependent ◽  
Single Channel Currents ◽  
K Currents

Voltage-dependent membrane currents of cells dissociated from tongues of larval tiger salamanders (Ambystoma tigrinum) were studied using whole-cell and single-channel patch-clamp techniques. Nongustatory epithelial cells displayed only passive membrane properties. Cells dissociated from taste buds, presumed to be gustatory receptor cells, generated both inward and outward currents in response to depolarizing voltage steps from a holding potential of -60 or -80 mV. Almost all taste cells displayed a transient inward current that activated at -30 mV, reached a peak between 0 and +10 mV and rapidly inactivated. This inward current was blocked by tetrodotoxin (TTX) or by substitution of choline for Na+ in the bath solution, indicating that it was a Na+ current. Approximately 60% of the taste cells also displayed a sustained inward current which activated slowly at about -30 mV and reached a peak at 0 to +10 mV. The amplitude of the slow inward current was larger when Ca2+ was replaced by Ba2+ and it was blocked by bath applied CO2+, indicating it was a Ca2+ current. Delayed outward K+ currents were observed in all taste cells although in about 10% of the cells, they were small and activated only at voltages more depolarized than +10 mV. Normally, K+ currents activated at -40 mV and usually showed some inactivation during a 25-ms voltage step. The inactivating component of outward current was not observed at holding potentials more depolarized -40 mV. The outward currents were blocked by tetraethylammonium chloride (TEA) and BaCl2 in the bath or by substitution of Cs+ for K+ in the pipette solution. Both transient and noninactivating components of outward current were partially suppressed by CO2+, suggesting the presence of a Ca2(+)-activated K+ current component. Single-channel currents were recorded in cell-attached and outside-out patches of taste cell membranes. Two types of K+ channels were partially characterized, one having a mean unitary conductance of 21 pS, and the other, a conductance of 148 pS. These experiments demonstrate that tiger salamander taste cells have a variety of voltage- and ion-dependent currents including Na+ currents, Ca2+ currents and three types of K+ currents. One or more of these conductances may be modulated either directly by taste stimuli or indirectly by stimulus-regulated second messenger systems to give rise to stimulus-activated receptor potentials. Others may play a role in modulation of neurotransmitter release at synapses with taste nerve fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

Structural Correlates of K+ Channel Function

Physiology ◽  
1994 ◽  
Vol 9 (4) ◽  
pp. 169-173 ◽  
Author(s):  
M Taglialatela ◽  
AM Brown
Keyword(s):  
Ion Channel ◽  
Ionic Currents ◽  
The Other ◽  
K Channel ◽  
K Channels ◽  
Functional Studies ◽  
Channel Function ◽  
Voltage Dependent ◽  
K Currents

More complementary DNAs have been cloned for Voltage-dependent K+ channels than any other voltage-dependent ion channel. Purely functional studies anticipated this result because K+ currents are far more diverse than voltage-dependent Na+, Ca2+, or Cl currents, the other types of voltage-dependent ionic currents commonly dealt with.

scholarly journals The Inhibition by Oxaliplatin, a Platinum-Based Anti-Neoplastic Agent, of the Activity of Intermediate-Conductance Ca2+-Activated K+ Channels in Human Glioma Cells

2015 ◽  
Vol 37 (4) ◽  
pp. 1390-1406 ◽  
Author(s):  
Mei-Han Huang ◽  
Yan-Ming Huang ◽  
Sheng-Nan Wu
Keyword(s):  
Cancer Cells ◽  
Single Channel ◽  
Glioma Cells ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
K Channels ◽  
And Migration ◽  
Ikca Channel ◽  
K Currents

Oxaliplatin (OXAL) is a third-generation organoplatinum which is effective against advanced cancer cells including glioma cells. How this agent and other related compounds interacts with ion channels in glioma cells is poorly understood. OXAL (100 µM) suppressed the amplitude of whole-cell K+ currents (IK); and, either DCEBIO or ionomycin significantly reversed OXAL-mediated inhibition of IK in human 13-06-MG glioma cells. In OXAL-treated cells, TRAM-34 did not suppress IK amplitude in these cells. The intermediate-conductance Ca2+-activated K+ (IKCa) channels subject to activation by DCEBIO and to inhibition by TRAM-34 or clotrimazole were functionally expressed in these cells. Unlike cisplatin, OXAL decreased the probability of IKCa-channel openings in a concentration-dependent manner with an IC50 value of 67 µM. No significant change in single-channel conductance of IKCa channels in the presence of OXAL was demonstrated. Neither large-conductance Ca2+-activated K+ channels nor inwardly rectifying K+ currents in these cells were affected in the presence of OXAL. OXAL also suppressed the proliferation and migration of 13-06-MG cells in a concentration- and time-dependent manner. OXAL reduced IKCa-channel activity in LoVo colorectal cancer cells. Taken together, the inhibition by OXAL of IKCa channels would conceivably be an important mechanism through which it acts on the functional activities of glioma cells occurring in vivo.

scholarly journals Block by calcium of ATP-activated channels in pheochromocytoma cells.

1993 ◽  
Vol 101 (3) ◽  
pp. 377-392 ◽  
Author(s):  
K Nakazawa ◽  
P Hess
Keyword(s):  
Patch Clamp ◽  
Single Channel ◽  
Divalent Cations ◽  
Mean Amplitude ◽  
Inhibitory Effect ◽  
Hill Coefficient ◽  
Similar Reduction ◽  
Site Model ◽  
Channel Current ◽  
Voltage Dependent

We have investigated the effects of Ca2+ on Na+ influx through ATP-activated channels in pheochromocytoma PC12 cells using single channel current recordings. Under cell-attached patch-clamp conditions with 150 mM Na+ and 2 mM Ca2+ in the pipette, the unitary current activity showed an open level of about -4.3 pA at -150 mV. The channel opening was interrupted by flickery noise as well as occasional transition to a subconducting state of about -1.7 pA at -150 mV. The open level was decreased with increased external Ca2+, suggesting that external Ca2+ blocks Na+ permeation. We assessed the block by Ca2+ as the mean amplitude obtained with heavy filtration according to Pietrobon et al. (Pietrobon, D., B. Prod'hom, and P. Hess, 1989. J. Gen. Physiol. 94:1-21). The block was concentration dependent with a Hill coefficient of 1 and a half-maximal concentration of approximately 6 mM. A similar block was observed with other divalent cations, and the order of potency was Cd2+ > Mn2+ > Mg2+ not equal to Ca2+ > Ba2+. High Ca2+, Mg2+ and Ba2+ did not block completely, probably because they can carry current in the channel. The block by external Ca2+ did not exhibit voltage dependence between -100 and -210 mV. In the inside-out patch-clamp configuration, the amplitude of inward channel current obtained with 150 mM external Na+ was reduced by increased internal Ca2+. The reduction was observed at lower concentrations than that by external Ca2+. Internal Ba2+ and Cd2+ induced similar reduction in current amplitude. This inhibitory effect of internal Ca2+ was voltage dependent; the inhibition was relieved with hyperpolarization. The results suggest that both external and internal Ca2+ can block Na+ influx through the ATP-activated channel. A simple one-binding site model with symmetric energy barriers is not sufficient to explain the Ca2+ block from both sides.

scholarly journals Effective Perturbations of the Amplitude, Gating, and Hysteresis of IK(DR) Caused by PT-2385, an HIF-2α Inhibitor

Membranes ◽  
2021 ◽  
Vol 11 (8) ◽  
pp. 636
Author(s):  
Hung-Tsung Hsiao ◽  
Guan-Ling Lu ◽  
Yen-Chin Liu ◽  
Sheng-Nan Wu
Keyword(s):  
Slow Component ◽  
Surface Membrane ◽  
Glioma Cells ◽  
Ionic Currents ◽  
Gh3 Cells ◽  
Delayed Rectifier ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Inactivation Curve

PT-2385 is currently regarded as a potent and selective inhibitor of hypoxia-inducible factor-2α (HIF-2α), with potential antineoplastic activity. However, the membrane ion channels changed by this compound are obscure, although it is reasonable to assume that the compound might act on surface membrane before entering the cell´s interior. In this study, we intended to explore whether it and related compounds make any adjustments to the plasmalemmal ionic currents of pituitary tumor (GH3) cells and human 13-06-MG glioma cells. Cell exposure to PT-2385 suppressed the peak or late amplitude of delayed-rectifier K+ current (IK(DR)) in a time- and concentration-dependent manner, with IC50 values of 8.1 or 2.2 µM, respectively, while the KD value in PT-2385-induced shortening in the slow component of IK(DR) inactivation was estimated to be 2.9 µM. The PT-2385-mediated block of IK(DR) in GH3 cells was little-affected by the further application of diazoxide, cilostazol, or sorafenib. Increasing PT-2385 concentrations shifted the steady-state inactivation curve of IK(DR) towards a more hyperpolarized potential, with no change in the gating charge of the current, and also prolonged the time-dependent recovery of the IK(DR) block. The hysteretic strength of IK(DR) elicited by upright or inverted isosceles-triangular ramp voltage was decreased during exposure to PT-2385; meanwhile, the activation energy involved in the gating of IK(DR) elicitation was noticeably raised in its presence. Alternatively, the presence of PT-2385 in human 13-06-MG glioma cells effectively decreased the amplitude of IK(DR). Considering all of the experimental results together, the effects of PT-2385 on ionic currents demonstrated herein could be non-canonical and tend to be upstream of the inhibition of HIF-2α. This action therefore probably contributes to down-streaming mechanisms through the changes that it or other structurally resemblant compounds lead to in the perturbations of the functional activities of pituitary cells or neoplastic astrocytes, in the case that in vivo observations occur.

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