scholarly journals Characterization of Inhibitory Effectiveness in Hyperpolarization-Activated Cation Currents by a Group of ent-Kaurane-Type Diterpenoids from Croton tonkinensis

2020 ◽  
Vol 21 (4) ◽  
pp. 1268 ◽  
Author(s):  
Ping-Chung Kuo ◽  
Yen-Chin Liu ◽  
Yi-Ching Lo ◽  
Sheng-Nan Wu
Keyword(s):  
Ionic Currents ◽  
Neuroendocrine Cells ◽  
Flowering Plant ◽  
Gh3 Cells ◽  
Functional Activities ◽  
Cation Current ◽  
Voltage Dependent ◽  
K Current ◽  
The Common

Croton is an extensive flowering plant genus in the spurge family, Euphorbiaceae. Three croton compounds with the common ent-kaurane skeleton have been purified from Croton tonkinensis. Methods: We examined any modifications of croton components (i.e., croton-01 [ent-18-acetoxy-7α-hydroxykaur-16-en-15-one], croton-02 [ent-7α,14β-dihydroxykaur-16-en-15-one] and croton-03 [ent-1β-acetoxy-7α,14β-dihydroxykaur-16-en-15-one] on either hyperpolarization-activated cation current (Ih) or erg-mediated K+ current identified in pituitary tumor (GH3) cells and in rat insulin-secreting (INS-1) cells via patch-clamp methods. Results: Addition of croton-01, croton-02, or croton-03 effectively and differentially depressed Ih amplitude. Croton-03 (3 μM) shifted the activation curve of Ih to a more negative potential by approximately 11 mV. The voltage-dependent hysteresis of Ih was also diminished by croton-03 administration. Croton-03-induced depression of Ih could not be attenuated by SQ-22536 (10 μM), an inhibitor of adenylate cyclase, but indeed reversed by oxaliplatin (10 μM). The Ih in INS-1 cells was also depressed effectively by croton-03. Conclusion: Our study highlights the evidence that these ent-kaurane diterpenoids might conceivably perturb these ionic currents through which they have high influence on the functional activities of endocrine or neuroendocrine cells.

scholarly journals Effectiveness in Block by Dexmedetomidine of Hyperpolarization-Activated Cation Current, Independent of Its Agonistic Effect on α2-Adrenergic Receptors

2020 ◽  
Vol 21 (23) ◽  
pp. 9110
Author(s):  
Te-Ling Lu ◽  
Te-Jung Lu ◽  
Sheng-Nan Wu
Keyword(s):  
Adrenergic Receptors ◽  
Time Course ◽  
Ionic Currents ◽  
Inhibitory Effect ◽  
Firing Frequency ◽  
Neuroendocrine Cells ◽  
Gh3 Cells ◽  
Membrane Excitability ◽  
Cation Current

Dexmedetomidine (DEX), a highly selective agonist of α2-adrenergic receptors, has been tailored for sedation without risk of respiratory depression. Our hypothesis is that DEX produces any direct perturbations on ionic currents (e.g., hyperpolarization-activated cation current, Ih). In this study, addition of DEX to pituitary GH3 cells caused a time- and concentration-dependent reduction in the amplitude of Ih with an IC50 value of 1.21 μM and a KD value of 1.97 μM. A hyperpolarizing shift in the activation curve of Ih by 10 mV was observed in the presence of DEX. The voltage-dependent hysteresis of Ih elicited by long-lasting triangular ramp pulse was also dose-dependently reduced during its presence. In continued presence of DEX (1 μM), further addition of OXAL (10 μM) or replacement with high K+ could reverse DEX-mediated inhibition of Ih, while subsequent addition of yohimbine (10 μM) did not attenuate the inhibitory effect on Ih amplitude. The addition of 3 μM DEX mildly suppressed the amplitude of erg-mediated K+ current. Under current-clamp potential recordings, the exposure to DEX could diminish the firing frequency of spontaneous action potentials. In pheochromocytoma PC12 cells, DEX was effective at suppressing Ih together with a slowing in activation time course of the current. Taken together, findings from this study strongly suggest that during cell exposure to DEX used at clinically relevant concentrations, the DEX-mediated block of Ih appears to be direct and would particularly be one of the ionic mechanisms underlying reduced membrane excitability in the in vivo endocrine or neuroendocrine cells.

scholarly journals Characterization of Convergent Suppression by UCL-2077 (3-(Triphenylmethylaminomethyl)pyridine), Known to Inhibit Slow Afterhyperpolarization, of erg-Mediated Potassium Currents and Intermediate-Conductance Calcium-Activated Potassium Channels

2020 ◽  
Vol 21 (4) ◽  
pp. 1441 ◽  
Author(s):  
Hung-Te Hsu ◽  
Yi-Ching Lo ◽  
Sheng-Nan Wu
Keyword(s):  
Ionic Currents ◽  
Gh3 Cells ◽  
Excitable Cells ◽  
Activation Curve ◽  
K Channels ◽  
Kd Values ◽  
K Current ◽  
Calcium Activated Potassium Channels ◽  
Voltage Hysteresis

UCL-2077 (triphenylmethylaminomethyl)pyridine) was previously reported to suppress slow afterhyperpolarization in neurons. However, the information with respect to the effects of UCL-2077 on ionic currents is quite scarce. The addition of UCL-2077 decreased the amplitude of erg-mediated K+ current (IK(erg)) together with an increased deactivation rate of the current in pituitary GH3 cells. The IC50 and KD values of UCL-2077-induced inhibition of IK(erg) were 4.7 and 5.1 μM, respectively. UCL-2077 (10 μM) distinctly shifted the midpoint in the activation curve of IK(erg) to less hyperpolarizing potentials by 17 mV. Its presence decreased the degree of voltage hysteresis for IK(erg) elicitation by long-lasting triangular ramp pulse. It also diminished the probability of the opening of intermediate-conductance Ca2+-activated K+ channels. In cell-attached current recordings, UCL-2077 raised the frequency of action currents. When KCNH2 mRNA was knocked down, a UCL-2077-mediated increase in AC firing was attenuated. Collectively, the actions elaborated herein conceivably contribute to the perturbating effects of this compound on electrical behaviors of excitable cells.

scholarly journals High Capability of Pentagalloylglucose (PGG) in Inhibiting Multiple Types of Membrane Ionic Currents

2020 ◽  
Vol 21 (24) ◽  
pp. 9369
Author(s):  
Wei-Ting Chang ◽  
Ping-Yen Liu ◽  
Sheng-Nan Wu
Keyword(s):  
Ionic Currents ◽  
Gh3 Cells ◽  
Delayed Rectifier ◽  
Oxidative Property ◽  
Ic50 Value ◽  
Voltage Dependent ◽  
Ramp Voltage ◽  
Pentagalloyl Glucose ◽  
K Current ◽  
Membrane Ionic Currents

Pentagalloyglucose (PGG, penta-O-galloyl-β-d-glucose; 1,2,3,4,6-pentagalloyl glucose), a pentagallic acid ester of glucose, is recognized to possess anti-bacterial, anti-oxidative and anti-neoplastic activities. However, to what extent PGG or other polyphenolic compounds can perturb the magnitude and/or gating of different types of plasmalemmal ionic currents remains largely uncertain. In pituitary tumor (GH3) cells, we found out that PGG was effective at suppressing the density of delayed-rectifier K+ current (IK(DR)) concentration-dependently. The addition of PGG could suppress the density of proton-activated Cl− current (IPAC) observed in GH3 cells. The IC50 value required for the inhibitory action of PGG on IK(DR) or IPAC observed in GH3 cells was estimated to be 3.6 or 12.2 μM, respectively, while PGG (10 μM) mildly inhibited the density of the erg-mediated K+ current or voltage-gated Na+ current. The presence of neither chlorotoxin, hesperetin, kaempferol, morin nor iberiotoxin had any effects on IPAC density, whereas hydroxychloroquine or 4-[(2-butyl-6,7-dichloro-2-cyclopentyl-2,3-dihydro-1-oxo-1H-inden-5yl)oxy] butanoic acid suppressed current density effectively. The application of PGG also led to a decrease in the area of voltage-dependent hysteresis of IPAC elicited by long-lasting isosceles-triangular ramp voltage command, suggesting that hysteretic strength was lessened in its presence. In human cardiac myocytes, the exposure to PGG also resulted in a reduction of ramp-induced IK(DR) density. Taken literally, PGG-perturbed adjustment of ionic currents could be direct and appears to be independent of its anti-oxidative property.

scholarly journals Effectiveness in the Block by Honokiol, a Dimerized Allylphenol from Magnolia Officinalis, of Hyperpolarization-Activated Cation Current and Delayed-Rectifier K+ Current

2020 ◽  
Vol 21 (12) ◽  
pp. 4260
Author(s):  
Ming-Huan Chan ◽  
Hwei-Hsien Chen ◽  
Yi-Ching Lo ◽  
Sheng-Nan Wu
Keyword(s):  
Surface Membrane ◽  
Ionic Currents ◽  
Gh3 Cells ◽  
Delayed Rectifier ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Voltage Dependent ◽  
K Current ◽  
Magnolia Officinalis

Background: Honokiol (HNK), a dimer of allylphenol obtained from the bark of Magnolia officinalis was demonstrated to exert an array of biological actions in different excitable cell types. However, whether or how this compound can lead to any perturbations on surface–membrane ionic currents remains largely unknown. Methods: We used the patch clamp method and found that addition of HNK effectively depressed the density of macroscopic hyperpolarization-activated cation currents (Ih) in pituitary GH3 cells in a concentration-, time- and voltage-dependent manner. By the use of a two-step voltage protocol, the presence of HNK (10 μM) shifted the steady-state activation curve of Ih density along the voltage axis to a more negative potential by approximately 11 mV, together with no noteworthy modification in the gating charge of the current. Results: The voltage-dependent hysteresis of Ih density elicited by long-lasting triangular ramp pulse was attenuated by the presence of HNK. The HNK addition also diminished the magnitude of deactivating Ih density elicited by ramp-up depolarization with varying durations. The effective half-maximal concentration (IC50) value needed to inhibit the density of Ih or delayed rectifier K+ current identified in GH3 cells was estimated to be 2.1 or 6.8 μM, respectively. In cell-attached current recordings, HNK decreased the frequency of spontaneous action currents. In Rolf B1.T olfactory sensory neurons, HNK was also observed to decrease Ih density in a concentration-dependent manner. Conclusions: The present study highlights the evidence revealing that HNK has the propensity to perturb these ionic currents and that the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel is proposed to be a potential target for the in vivo actions of HNK and its structurally similar compounds.

scholarly journals Characterization of the Synergistic Inhibition of IK(erg) and IK(DR) by Ribociclib, a Cyclin-Dependent Kinase 4/6 Inhibitor

2020 ◽  
Vol 21 (21) ◽  
pp. 8078
Author(s):  
Pin-Yen Liu ◽  
Wei-Ting Chang ◽  
Sheng-Nan Wu
Keyword(s):  
Pituitary Tumor ◽  
Time Course ◽  
Transforming Growth Factor ◽  
Ionic Currents ◽  
Transforming Growth Factor Β ◽  
Gh3 Cells ◽  
Delayed Rectifier ◽  
Cyclin Dependent Kinase ◽  
Cation Current ◽  
K Current

Ribociclib (RIB, LE011, Kisqali®), an orally administered inhibitor of cyclin-dependent kinase-4/6 (CDK-4/6) complex, is clinically effective for the treatment of several malignancies, including advanced breast cancer. However, information regarding the effects of RIB on membrane ion currents is limited. In this study, the addition of RIB to pituitary tumor (GH3) cells decreased the peak amplitude of erg-mediated K+ current (IK(erg)), which was accompanied by a slowed deactivation rate of the current. The IC50 value for RIB-perturbed inhibition of deactivating IK(erg) in these cells was 2.7 μM. In continued presence of μM RIB, neither the subsequent addition of 17β-estradiol (30 μM), phorbol 12-myristate 13-acetate (10 μM), or transforming growth factor-β (1 μM) counteracted the inhibition of deactivating IK(erg). Its presence affected the decrease in the degree of voltage-dependent hysteresis for IK(erg) elicitation by long-duration triangular ramp voltage commands. The presence of RIB differentially inhibited the peak or sustained component of delayed rectifier K+ current (IK(DR)) with an effective IC50 of 28.7 or 11.4 μM, respectively, while it concentration-dependently decreased the amplitude of M-type K+ current with IC50 of 13.3 μM. Upon 10-s long membrane depolarization, RIB elicited a decrease in the IK(DR) amplitude, which was concomitant with an accelerated inactivation time course. However, the inability of RIB (10 μM) to modify the magnitude of the hyperpolarization-activated cation current was disclosed. The mean current–voltage relationship of IK(erg) present in HL-1 atrial cardiomyocytes was inhibited in the presence of RIB (10 μM). Collectively, the hyperpolarization-activated cation current was observed. RIB-mediated perturbations in ionic currents presented herein are upstream of its suppressive action on cytosolic CDK-4/6 activities and partly participates in its modulatory effects on the functional activities of pituitary tumor cells (e.g., GH3 cells) or cardiac myocytes (e.g., HL-1 cells).

scholarly journals Characterization of Direct Perturbations on Voltage-Gated Sodium Current by Esaxerenone, a Nonsteroidal Mineralocorticoid Receptor Blocker

Biomedicines ◽  
2021 ◽  
Vol 9 (5) ◽  
pp. 549
Author(s):  
Wei-Ting Chang ◽  
Sheng-Nan Wu
Keyword(s):  
Mineralocorticoid Receptor ◽  
Sodium Current ◽  
Ionic Currents ◽  
Antagonistic Effect ◽  
Gh3 Cells ◽  
Excitable Cells ◽  
Voltage Gated ◽  
Ic50 Value ◽  
Low Threshold

Esaxerenone (ESAX; CS-3150, Minnebro®) is known to be a newly non-steroidal mineralocorticoid receptor (MR) antagonist. However, its modulatory actions on different types of ionic currents in electrically excitable cells remain largely unanswered. The present investigations were undertaken to explore the possible perturbations of ESAX on the transient, late and persistent components of voltage-gated Na+ current (INa) identified from pituitary GH3 or MMQ cells. GH3-cell exposure to ESAX depressed the transient and late components of INa with varying potencies. The IC50 value of ESAX required for its differential reduction in peak or late INa in GH3 cells was estimated to be 13.2 or 3.2 μM, respectively. The steady-state activation curve of peak INa remained unchanged during exposure to ESAX; however, recovery of peak INa block was prolonged in the presence 3 μM ESAX. In continued presence of aldosterone (10 μM), further addition of 3 μM ESAX remained effective at inhibiting INa. ESAX (3 μM) potently reversed Tef-induced augmentation of INa. By using isosceles-triangular ramp pulse with varying durations, the amplitude of persistent INa measured at high or low threshold was enhanced by the presence of tefluthrin (Tef), in combination with the appearance of the figure-of-eight hysteretic loop; moreover, hysteretic strength of the current was attenuated by subsequent addition of ESAX. Likewise, in MMQ lactotrophs, the addition of ESAX also effectively decreased the peak amplitude of INa along with the increased current inactivation rate. Taken together, the present results provide a noticeable yet unidentified finding disclosing that, apart from its antagonistic effect on MR receptor, ESAX may directly and concertedly modify the amplitude, gating properties and hysteresis of INa in electrically excitable cells.

scholarly journals The Effectiveness in Activating M-Type K+ Current Produced by Solifenacin ([(3R)-1-azabicyclo[2.2.2]octan-3-yl] (1S)-1-phenyl-3,4-dihydro-1H-isoquinoline-2-carboxylate): Independent of Its Antimuscarinic Action

2021 ◽  
Vol 22 (22) ◽  
pp. 12399
Author(s):  
Hsin-Yen Cho ◽  
Tzu-Hsien Chuang ◽  
Sheng-Nan Wu
Keyword(s):  
Single Channel ◽  
Ionic Currents ◽  
Reaction Scheme ◽  
Gh3 Cells ◽  
Whole Cell ◽  
Type K ◽  
Cell Current ◽  
K Current ◽  
Subsequent Addition ◽  
Whole Cell Current

Solifenacin (Vesicare®, SOL), known to be a member of isoquinolines, is a muscarinic antagonist that has anticholinergic effect, and it has been beneficial in treating urinary incontinence and neurogenic detrusor overactivity. However, the information regarding the effects of SOL on membrane ionic currents is largely uncertain, despite its clinically wide use in patients with those disorders. In this study, the whole-cell current recordings revealed that upon membrane depolarization in pituitary GH3 cells, the exposure to SOL concentration-dependently increased the amplitude of M-type K+ current (IK(M)) with effective EC50 value of 0.34 μM. The activation time constant of IK(M) was concurrently shortened in the SOL presence, hence yielding the KD value of 0.55 μM based on minimal reaction scheme. As cells were exposed to SOL, the steady-state activation curve of IK(M) was shifted along the voltage axis to the left with no change in the gating charge of the current. Upon an isosceles-triangular ramp pulse, the hysteretic area of IK(M) was increased by adding SOL. As cells were continually exposed to SOL, further application of acetylcholine (1 μM) failed to modify SOL-stimulated IK(M); however, subsequent addition of thyrotropin releasing hormone (TRH, 1 μM) was able to counteract SOL-induced increase in IK(M) amplitude. In cell-attached single-channel current recordings, bath addition of SOL led to an increase in the activity of M-type K+ (KM) channels with no change in the single channel conductance; the mean open time of the channel became lengthened. In whole-cell current-clamp recordings, the SOL application reduced the firing of action potentials (APs) in GH3 cells; however, either subsequent addition of TRH or linopirdine was able to reverse SOL-mediated decrease in AP firing. In hippocampal mHippoE-14 neurons, the IK(M) was also stimulated by adding SOL. Altogether, findings from this study disclosed for the first time the effectiveness of SOL in interacting with KM channels and hence in stimulating IK(M) in electrically excitable cells, and this noticeable action appears to be independent of its antagonistic activity on the canonical binding to muscarinic receptors expressed in GH3 or mHippoE-14 cells.

Characterization of a hyperpolarization-activated cation current in rat pituitary cells

1997 ◽  
Vol 272 (3) ◽  
pp. E405-E414 ◽  
Author(s):  
S. M. Simasko ◽  
S. Sankaranarayanan
Keyword(s):  
Primary Cultures ◽  
Gh3 Cells ◽  
Pituitary Cells ◽  
Sodium Permeability ◽  
Cation Current ◽  
Whole Cell Patch Clamp ◽  
Bath Application ◽  
Rat Pituitary ◽  
Rat Pituitary Cells

Whole cell patch-clamp techniques were used on clonal pituitary cells (GH3) and primary cultures of somatotrophs and lactotrophs to study currents that would be active at or below voltages for the threshold for action potential generation. When GH3 cells were held at -60 mV and pulsed to -120 mV, a slow-activating sustained inward current was observed (-16.5 +/- 1.5 pA in physiological baths, n = 72; approximately 1 s to half-maximal activation, voltage for 50% activation - 101 mV). The current was insensitive to bath application of 10 mM tetraethylammonium, 10 mM 4-aminopyridine, and 1 mM barium but was completely blocked by 3 mM cesium. The current was found to be a mixed cation current with a sodium permeability of 0.29 relative to potassium. These properties indicate that the current belongs to the hyperpolarization-activated cation current (Ih), or I(f), family of currents. However, the current was not altered by the addition of adenosine 3',5'-cyclic monophosphate (cAMP) to the pipette or forskolin to the bath. A similar but smaller current was observed in 15 of 16 somatotrophs but in only 1 of 9 lactotrophs. Application of cesium to spontaneously spiking GH3 cells or somatotrophs had no effect. However, cesium did block an inward holding current observed at -80 mV. These results demonstrate that the I(h) in pituitary cells does not serve as a pacemaking current but suggest that it may influence membrane potential responses when somatotrophs become hyperpolarized.

scholarly journals Synergistic Inhibition of Delayed Rectifier K+ and Voltage-Gated Na+ Currents by Artemisinin in Pituitary Tumor (GH3) Cells

2017 ◽  
Vol 41 (5) ◽  
pp. 2053-2066 ◽  
Author(s):  
Edmund Cheung So ◽  
Sheng-Nan Wu ◽  
Ping-Ching Wu ◽  
Hui-Zhen  Chen ◽  
Chia-Jung Yang
Keyword(s):  
Pituitary Tumor ◽  
Ionic Currents ◽  
Neuroendocrine Cells ◽  
Endocrine Function ◽  
Gh3 Cells ◽  
Delayed Rectifier ◽  
Membrane Excitability ◽  
Inactivation Curve ◽  
Voltage Gated

Background: Artemisinin (ART) is an anti-malarial agent reported to influence endocrine function. Methods: Effects of ART on ionic currents and action potentials (APs) in pituitary tumor (GH3) cells were evaluated by patch clamp techniques. Results: ART inhibited the amplitude of delayed-rectifier K+ current (IK(DR)) in response to membrane depolarization and accelerated the process of current inactivation. It exerted an inhibitory effect on IK(DR) with an IC50 value of 11.2 µM and enhanced IK(DR) inactivation with a KD value of 14.7 µM. The steady-state inactivation curve of IK(DR) was shifted to hyperpolarization by 10 mV. Pretreatment of chlorotoxin (1 µM) or iloprost (100 nM) did not alter the magnitude of ART-induced inhibition of IK(DR) in GH3 cells. ART also decreased the peak amplitude of voltage-gated Na+ current (INa) with a concentration-dependent slowing in inactivation rate. Application of KMUP-1, an inhibitor of late INa, was effective at reversing ART-induced prolongation in inactivation time constant of INa. Under current-clamp recordings, ART alone reduced the amplitude of APs and prolonged the duration of APs. Conclusion: Under ART exposure, the inhibitory actions on both IK(DR) and INa could be a potential mechanisms through which this drug influences membrane excitability of endocrine or neuroendocrine cells appearing in vivo.

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