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Effective Perturbations of the Amplitude, Gating, and Hysteresis of IK(DR) Caused by PT-2385, an HIF-2α Inhibitor. MEMBRANES 2021; 11:membranes11080636. [PMID: 34436399 PMCID: PMC8398179 DOI: 10.3390/membranes11080636] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/30/2021] [Revised: 08/06/2021] [Accepted: 08/10/2021] [Indexed: 01/30/2023]
Abstract
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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Garner BR, Stolarz AJ, Stuckey D, Sarimollaoglu M, Liu Y, Palade PT, Rusch NJ, Mu S. K ATP Channel Openers Inhibit Lymphatic Contractions and Lymph Flow as a Possible Mechanism of Peripheral Edema. J Pharmacol Exp Ther 2021; 376:40-50. [PMID: 33100270 PMCID: PMC7745085 DOI: 10.1124/jpet.120.000121] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2020] [Accepted: 10/08/2020] [Indexed: 11/22/2022] Open
Abstract
Pharmacological openers of ATP-sensitive potassium (KATP) channels are effective antihypertensive agents, but off-target effects, including severe peripheral edema, limit their clinical usefulness. It is presumed that the arterial dilation induced by KATP channel openers (KCOs) increases capillary pressure to promote filtration edema. However, KATP channels also are expressed by lymphatic muscle cells (LMCs), raising the possibility that KCOs also attenuate lymph flow to increase interstitial fluid. The present study explored the effect of KCOs on lymphatic contractile function and lymph flow. In isolated rat mesenteric lymph vessels (LVs), the prototypic KATP channel opener cromakalim (0.01-3 µmol/l) progressively inhibited rhythmic contractions and calculated intraluminal flow. Minoxidil sulfate and diazoxide (0.01-100 µmol/l) had similar effects at clinically relevant plasma concentrations. High-speed in vivo imaging of the rat mesenteric lymphatic circulation revealed that superfusion of LVs with cromakalim and minoxidil sulfate (0.01-10 µmol/l) maximally decreased lymph flow in vivo by 38.4% and 27.4%, respectively. Real-time polymerase chain reaction and flow cytometry identified the abundant KATP channel subunits in LMCs as the pore-forming Kir6.1/6.2 and regulatory sulfonylurea receptor 2 subunits. Patch-clamp studies detected cromakalim-elicited unitary K+ currents in cell-attached patches of LMCs with a single-channel conductance of 46.4 pS, which is a property consistent with Kir6.1/6.2 tetrameric channels. Addition of minoxidil sulfate and diazoxide elicited unitary currents of similar amplitude. Collectively, our findings indicate that KCOs attenuate lymph flow at clinically relevant plasma concentrations as a potential contributing mechanism to peripheral edema. SIGNIFICANCE STATEMENT: ATP-sensitive potassium (KATP) channel openers (KCOs) are potent antihypertensive medications, but off-target effects, including severe peripheral edema, limit their clinical use. Here, we demonstrate that KCOs impair the rhythmic contractions of lymph vessels and attenuate lymph flow, which may promote edema formation. Our finding that the KATP channels in lymphatic muscle cells may be unique from their counterparts in arterial muscle implies that designing arterial-selective KCOs may avoid activation of lymphatic KATP channels and peripheral edema.
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Affiliation(s)
- Brittney R Garner
- Department of Pharmacology and Toxicology (B.R.G., A.J.S., D.S., Y.L., P.T.P., N.J.R., S.M.) and Arkansas Nanomedicine Center (M.S.), College of Medicine and Department of Pharmaceutical Sciences, College of Pharmacy (A.J.S.), University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Amanda J Stolarz
- Department of Pharmacology and Toxicology (B.R.G., A.J.S., D.S., Y.L., P.T.P., N.J.R., S.M.) and Arkansas Nanomedicine Center (M.S.), College of Medicine and Department of Pharmaceutical Sciences, College of Pharmacy (A.J.S.), University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Daniel Stuckey
- Department of Pharmacology and Toxicology (B.R.G., A.J.S., D.S., Y.L., P.T.P., N.J.R., S.M.) and Arkansas Nanomedicine Center (M.S.), College of Medicine and Department of Pharmaceutical Sciences, College of Pharmacy (A.J.S.), University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Mustafa Sarimollaoglu
- Department of Pharmacology and Toxicology (B.R.G., A.J.S., D.S., Y.L., P.T.P., N.J.R., S.M.) and Arkansas Nanomedicine Center (M.S.), College of Medicine and Department of Pharmaceutical Sciences, College of Pharmacy (A.J.S.), University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Yunmeng Liu
- Department of Pharmacology and Toxicology (B.R.G., A.J.S., D.S., Y.L., P.T.P., N.J.R., S.M.) and Arkansas Nanomedicine Center (M.S.), College of Medicine and Department of Pharmaceutical Sciences, College of Pharmacy (A.J.S.), University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Philip T Palade
- Department of Pharmacology and Toxicology (B.R.G., A.J.S., D.S., Y.L., P.T.P., N.J.R., S.M.) and Arkansas Nanomedicine Center (M.S.), College of Medicine and Department of Pharmaceutical Sciences, College of Pharmacy (A.J.S.), University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Nancy J Rusch
- Department of Pharmacology and Toxicology (B.R.G., A.J.S., D.S., Y.L., P.T.P., N.J.R., S.M.) and Arkansas Nanomedicine Center (M.S.), College of Medicine and Department of Pharmaceutical Sciences, College of Pharmacy (A.J.S.), University of Arkansas for Medical Sciences, Little Rock, Arkansas
| | - Shengyu Mu
- Department of Pharmacology and Toxicology (B.R.G., A.J.S., D.S., Y.L., P.T.P., N.J.R., S.M.) and Arkansas Nanomedicine Center (M.S.), College of Medicine and Department of Pharmaceutical Sciences, College of Pharmacy (A.J.S.), University of Arkansas for Medical Sciences, Little Rock, Arkansas
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Wang W, Zheng D, Li H, Huang J, Chen H, Ying T, Fang J, Luo Y. Hemichannel-mediated volume regulation contributes to IPC-induced cardiomyocyte protection. Exp Ther Med 2018; 17:1847-1854. [PMID: 30783459 DOI: 10.3892/etm.2018.7127] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Accepted: 11/21/2018] [Indexed: 01/13/2023] Open
Abstract
Cx43 has been documented to be involved in ischemic preconditioning (IPC). However, the participation of Cx43-formed hemichannels in IPC and the potential underlying mechanisms remain unclear. The present study focused on cardiomyocytes' volume regulation during IPC to investigate the role of hemichannels in the IPC-induced cardioprotection. In the study, mice cardiomyocytes were respectively treated with a hemichannel blocker, octanol or 18a-Glycyrrhizic acid (18a-GA), and a Cx43-silenced lentivirus. They were subsequently cultured in hypotonic solution to simulate ischemic reperfusion (SIR) and systemic ischemic preconditioning (SIP). Cell morphology and volumetric (area) change were detected by inverted microscopy at 30 min following the addition of hypotonic solution. Cardiomyocyte mortality was assessed by trypan blue stain assay. The analyses revealed that regardless of the treatments, hypotonic solution aggravated cell edema: Compared with the initial condition (the moment before the solution addition, 0 min), the volumetric area increased significantly 30 min later (for hypotonic+DMSO, 5,050±1,511 vs. 3,464±723 µm2; for hypotonic+scramble lentiviral vector, 5,517±1,128 vs. 2,331±536 µm2; P<0.05, respectively). Either treatment alleviated the edematous condition when a comparison was made between 30 min after the hypotonic addition and 0 min (for hypotonic+octanol, 2,990±765 vs. 2,821±773 µm2; for hypotonic+18a-GA, 4,817±1,306 vs. 4,762±1,271 µm2; for hypotonic+Cx43-silenced, 3,627±688 vs. 3,419±814 µm2; P>0.05 for all). Notably, results indicated that the SIP group had lower mortality rates compared with its SIR counterpart; the hypotonic+octanol, hypotonic+18a-GA, and hypotonic+Cx43-silenced group showed markedly-declined mortality when compared with their respective control groups (respectively, 35.70±1.02, 30.76±2.20 vs. 53.58±2.14%; 30.89±2.37 vs. 54.12±2.55%; P<0.05 for all). The results suggest that ischemic preconditioning may provide cardioprotection by blocking the opening of the hemichannels and further mediating the volume regulation of cardiomyocytes.
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Affiliation(s)
- Wenying Wang
- Department of Cardiology, Fujian Medical University Union Hospital, Fujian Institute of Coronary Heart Disease, Fuzhou, Fujian 350001, P.R. China
| | - Dedong Zheng
- Department of Cardiology, Fujian Medical University Union Hospital, Fujian Institute of Coronary Heart Disease, Fuzhou, Fujian 350001, P.R. China
| | - Huiya Li
- Department of Cardiology, Fujian Medical University Union Hospital, Fujian Institute of Coronary Heart Disease, Fuzhou, Fujian 350001, P.R. China
| | - Jinhua Huang
- Department of Cardiology, Fujian Medical University Union Hospital, Fujian Institute of Coronary Heart Disease, Fuzhou, Fujian 350001, P.R. China
| | - Huijun Chen
- Department of Hematology, Fujian Medical University Union Hospital, Fujian Institute of Hematology, Fuzhou, Fujian 350001, P.R. China
| | - Teng Ying
- Department of Cardiology, Fujian Medical University Union Hospital, Fujian Institute of Coronary Heart Disease, Fuzhou, Fujian 350001, P.R. China
| | - Jun Fang
- Department of Cardiology, Fujian Medical University Union Hospital, Fujian Institute of Coronary Heart Disease, Fuzhou, Fujian 350001, P.R. China
| | - Yukun Luo
- Department of Cardiology, Fujian Medical University Union Hospital, Fujian Institute of Coronary Heart Disease, Fuzhou, Fujian 350001, P.R. China
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Tran PTH, Lee YH, Bhattarai JP, Park SJ, Yi HK, Han SK. Existence of ATP sensitive potassium currents on human periodontal ligament cells. Arch Oral Biol 2017; 76:48-54. [PMID: 28119170 DOI: 10.1016/j.archoralbio.2017.01.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Revised: 01/11/2017] [Accepted: 01/12/2017] [Indexed: 10/20/2022]
Abstract
OBJECTIVE Potassium channels of the ATP-sensitive family (KATP channel) are inhibited by increase in intracellular ATP. Electrophysiological studies have demonstrated that the kinetics and pharmacological properties of KATP channels vary among different tissues, suggesting structurally and functionally distinct types. There are studies showing human periodontal ligament (PDL) cells respond to mechanical stress by increasing ATP release, which participates in bone resorption or bone homeostasis. So, in this study we investigated the existence of KATP channel subunit and their single channel properties in human periodontal ligaments. MATERIALS & METHOD The human PDL cells were isolated from healthy erupted third molar. For patch-clamp experiments, human PDL fibroblasts were seeded on 3.5cm plastic dishes. The inside-out patch clamp recordings were performed under voltage clamp mode. Reverse transcriptase polymerase chain reaction (RT-PCR) was conducted to identify the channel subunits. All pair-wise comparisons were performed by Paired t-test. A P value <0.05 was considered significant. RESULTS We observed mRNA transcripts for Kir6.1, Kir6.2 and Sur2B subuits in the human PDL cells. In inside-out patch mode, the single channel conductance was 163pS at symmetrical K+ concentration of 140mM and inward rectification was seen in ATP-free bath solution. The reversal potential of the currents was found to be 0mV at symmetrical concentration (140mM) of K+ in bath solution. The single channel currents were almost blocked by adding 5mM ATP in the bath solution. However, the currents were not blocked by 100μM glibenclamide, a subunit specific KATP channel blocker. CONCLUSIONS These results indicate that human PDL cells express KATP channels subunit including Sur2B and Kir6.1 and Kir6.2 which are sensitive to ATP but insensitive to glibenclamide.
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Affiliation(s)
- Phuong Thi Huyen Tran
- Department of Oral Physiology, School of Dentistry & Institute of Oral Bioscience, Chonbuk National University, Jeonju, South Korea
| | - Young Hee Lee
- Department of Oral Biochemistry, School of Dentistry & Institute of Oral Bioscience, Chonbuk National University, Jeonju, South Korea
| | - Janardhan Prasad Bhattarai
- Department of Oral Physiology, School of Dentistry & Institute of Oral Bioscience, Chonbuk National University, Jeonju, South Korea
| | - Soo Joung Park
- Department of Oral Physiology, School of Dentistry & Institute of Oral Bioscience, Chonbuk National University, Jeonju, South Korea
| | - Ho-Keun Yi
- Department of Oral Biochemistry, School of Dentistry & Institute of Oral Bioscience, Chonbuk National University, Jeonju, South Korea
| | - Seong Kyu Han
- Department of Oral Physiology, School of Dentistry & Institute of Oral Bioscience, Chonbuk National University, Jeonju, South Korea.
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Abstract
KATP channels are integral to the functions of many cells and tissues. The use of electrophysiological methods has allowed for a detailed characterization of KATP channels in terms of their biophysical properties, nucleotide sensitivities, and modification by pharmacological compounds. However, even though they were first described almost 25 years ago (Noma 1983, Trube and Hescheler 1984), the physiological and pathophysiological roles of these channels, and their regulation by complex biological systems, are only now emerging for many tissues. Even in tissues where their roles have been best defined, there are still many unanswered questions. This review aims to summarize the properties, molecular composition, and pharmacology of KATP channels in various cardiovascular components (atria, specialized conduction system, ventricles, smooth muscle, endothelium, and mitochondria). We will summarize the lessons learned from available genetic mouse models and address the known roles of KATP channels in cardiovascular pathologies and how genetic variation in KATP channel genes contribute to human disease.
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Affiliation(s)
- Monique N Foster
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
| | - William A Coetzee
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
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Wu SN, Chen HZ, Chou YH, Huang YM, Lo YC. Inhibitory actions by ibandronate sodium, a nitrogen-containing bisphosphonate, on calcium-activated potassium channels in Madin-Darby canine kidney cells. Toxicol Rep 2015; 2:1182-1193. [PMID: 28962460 PMCID: PMC5598360 DOI: 10.1016/j.toxrep.2015.08.010] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Revised: 08/23/2015] [Accepted: 08/25/2015] [Indexed: 12/15/2022] Open
Abstract
The nitrogen-containing bisphosphonates used for management of the patients with osteoporosis were reported to influence the function of renal tubular cells. However, how nitrogen-containing bisphosphates exert any effects on ion currents remains controversial. The effects of ibandronate (Iban), a nitrogen-containing bisphosphonate, on ionic channels, including two types of Ca2+-activated K+ (KCa) channels, namely, large-conductance KCa (BKCa) and intermediate-conductance KCa (IKCa) channels, were investigated in Madin–Darby canine kidney (MDCK) cells. In whole-cell current recordings, Iban suppressed the amplitude of voltage-gated K+ current elicited by long ramp pulse. Addition of Iban caused a reduction of BKCa channels accompanied by a right shift in the activation curve of BKCa channels, despite no change in single-channel conductance. Ca2+ sensitivity of these channels was modified in the presence of this compound; however, the magnitude of Iban-mediated decrease in BKCa-channel activity under membrane stretch with different negative pressure remained unchanged. Iban suppressed the probability of BKCa-channel openings linked primarily to a shortening in the slow component of mean open time in these channels. The dissociation constant needed for Iban-mediated suppression of mean open time in MDCK cells was 12.2 μM. Additionally, cell exposure to Iban suppressed the activity of IKCa channels, and DC-EBIO or 9-phenanthrol effectively reversed its suppression. Under current-clamp configuration, Iban depolarized the cells and DC-EBIO or PF573228 reversed its depolarizing effect. Taken together, the inhibitory action of Iban on KCa-channel activity may contribute to the underlying mechanism of pharmacological or toxicological actions of Iban and its structurally similar bisphosphonates on renal tubular cells occurring in vivo.
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Key Words
- BKCa channel, large-conductance Ca2+-activated K+ channel
- DC-EBIO, 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one
- DMEM, Dulbecco’s modified Eagle’s medium
- FBS, fetal bovine serum
- H2S, hydrogen sulfide
- IK, voltage-gated K+ current
- IKCa channel, intermediate-conductance Ca2+-activated K+ channel
- Iban, ibandronate sodium
- Ibandronate
- Intermediate-conductance Ca2+-activated K+ channel
- I–V, current–voltage
- KCa channel, Ca2+-activated K+ channel
- KD, dissociation constant
- Large-conductance Ca2+-activated K+ channel
- MDCK cell
- MDCK cell, Madin–Darby canine kidney cell,NaHS, sodium hydrosulphide
- Membrane potential
- PF573228, 3,4-dihydro-6-[[4-[[[3-(methylsulfonyl)phenyl]methyl]amino]-5(trifluoromethyl)-2-pyrimidinyl]amino]-2(1H)-quinolinone
- SEM, standard error of the mean
- TRAM-34, 1-((2-chloropheny) (diphenyl)methyl)-1H-pyrazole
- [Ca2+]i, intracellular Ca2+ concentration
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Affiliation(s)
- Sheng-Nan Wu
- Department of Physiology, National Cheng Kung University Medical College, Tainan City, Taiwan
| | - Hui-Zhen Chen
- Department of Physiology, National Cheng Kung University Medical College, Tainan City, Taiwan
| | - Yu-Hung Chou
- School of Medicine, Mayne Medical School, University of Queensland, Brisbane, Queensland, Australia
| | - Yan-Ming Huang
- Department of Physiology, National Cheng Kung University Medical College, Tainan City, Taiwan
| | - Yi-Ching Lo
- Department of Pharmacology, Kaohsiung Medical University, Kaohsiung City, Taiwan
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Wu SN, Huang YM, Kao CA, Chen BS, Lo YC. Investigations on contribution of glial inwardly-rectifying K(+) current to membrane potential and ion flux: an experimental and theoretical study. Kaohsiung J Med Sci 2014; 31:9-17. [PMID: 25600915 DOI: 10.1016/j.kjms.2014.10.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Revised: 07/01/2014] [Accepted: 08/20/2014] [Indexed: 01/29/2023] Open
Abstract
The inwardly rectifying K(+) current [IK(IR)] allows large inward K(+) currents at potentials negative to K(+) equilibrium potential (EK) and it becomes small outward K(+) currents at those positive to EK. How changes of such currents enriched in glial cells can influence the functions of glial cell, neurons, or both is not clearly defined, although mutations of Kir4.1 channels have been demonstrated to cause serious neurological disorders. In this study, we identified the presence of IK(IR) in human glioma cells (U373 and U87 cells). The amplitude of IK(IR) in U373 cells was subject to inhibition by amitriptyline, arecoline, or BaCl2. The activity of inwardly rectifying K(+) channels was also clearly detected, and single-channel conductance of these channels was calculated to be around 23 pS. Moreover, based on a simulation model derived from neuron-glial interaction mediated by ion flux, we further found out that incorporation of glial IK(IR) conductance into the model can significantly contribute to regulation of extracellular K(+) concentrations and glial resting potential, particularly during high-frequency stimulation. Glial cells and neurons can mutually modulate their expression of ion channels through K(+) ions released into the extracellular space. It is thus anticipated that glial IK(IR) may be a potential target utilized to influence the activity of neuronal and glial cells as well as their interaction.
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Affiliation(s)
- Sheng-Nan Wu
- Department of Physiology, National Cheng Kung University Medical College, Tainan City, Taiwan; Institute of Basic Medical Sciences, National Cheng Kung University Medical College, Tainan City, Taiwan.
| | - Yan-Ming Huang
- Department of Physiology, National Cheng Kung University Medical College, Tainan City, Taiwan
| | - Ching-An Kao
- Department of Physiology, National Cheng Kung University Medical College, Tainan City, Taiwan
| | - Bing-Shuo Chen
- Department of Anaesthesiology, Chi-Mei Medical Center, Tainan City, Taiwan
| | - Yi-Ching Lo
- Department of Pharmacology, Kaohsiung Medical University, Kaohsiung City, Taiwan
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Inhibition of the cardiac ATP-dependent potassium current by KB-R7943. Comp Biochem Physiol A Mol Integr Physiol 2014; 175:38-45. [PMID: 24845199 DOI: 10.1016/j.cbpa.2014.05.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2014] [Revised: 05/12/2014] [Accepted: 05/13/2014] [Indexed: 11/23/2022]
Abstract
KB-R7943 (2-[2-[4-(4-nitrobenzyloxy)phenyl]ethyl]isothiourea) was developed as a specific inhibitor of the sarcolemmal sodium-calcium exchanger (NCX) with potential experimental and therapeutic use. However, in cardiomyocytes KB-R7943 also effectively blocks several K(+) currents including the delayed rectifier, IKr, and background inward rectifier, IK1. In the present study we analyze the effects of KB-R7943 on the ATP-dependent potassium current (IKATP) recorded by whole-cell patch-clamp in ventricular cardiomyocytes from a mammal (mouse) and a fish (crucian carp). IKATP was induced by external application of a mitochondrial uncoupler CCCP (3×10(-7) M) and internal perfusion of the cell with ATP-free pipette solution. A weakly inwardly rectifying current with a large outward component, recorded in the presence of CCCP, was blocked with 10(-5) M glibenclamide by 56.1±4.6% and 56.9±3.6% in crucian carp and mouse ventricular myocytes, respectively. In fish cardiomyocytes IKATP was blocked by KB-R7943 with an IC50 value of 3.14×10(-7) M, while in mammalian cells IC50 was 2.8×10(-6) M (P<0.05). 10(-5) M KB-R7943 inhibited CCCP-induced IKATP by 99.9±0.13% and 97.5±1.2% in crucian carp and mouse ventricular myocytes, respectively. In crucian carp the IKATP is about an order of magnitude more sensitive to KB-R7943 than the background IK1, but in mammals IKATP and IK1 are almost equally sensitive to KB-R7943. Therefore, the ability of KB-R7943 to block IKATP should be taken into account together with INCX inhibition when investigating possible cardioprotective effects of this compound.
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Burley DS, Cox CD, Zhang J, Wann KT, Baxter GF. Natriuretic peptides modulate ATP-sensitive K(+) channels in rat ventricular cardiomyocytes. Basic Res Cardiol 2014; 109:402. [PMID: 24477916 PMCID: PMC3951884 DOI: 10.1007/s00395-014-0402-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Revised: 12/10/2013] [Accepted: 01/10/2014] [Indexed: 11/28/2022]
Abstract
B-type natriuretic peptide (BNP) and C-type natriuretic peptide (CNP), and (Cys-18)-atrial natriuretic factor (4–23) amide (C-ANF), are cytoprotective under conditions of ischemia–reperfusion, limiting infarct size. ATP-sensitive K+ channel (KATP) opening is also cardioprotective, and although the KATP activation is implicated in the regulation of cardiac natriuretic peptide release, no studies have directly examined the effects of natriuretic peptides on cardiac KATP activity. Normoxic cardiomyocytes were patch clamped in the cell-attached configuration to examine sarcolemmal KATP (sKATP) activity. The KATP opener pinacidil (200 μM) increased the open probability of the patch (NPo; values normalized to control) at least twofold above basal value, and this effect was abolished by HMR1098 10 μM, a selective KATP blocker (5.23 ± 1.20 versus 0.89 ± 0.18; P < 0.001). We then examined the effects of BNP, CNP, C-ANF and 8Br-cGMP on the sKATP current. Bath application of BNP (≥10 nM) or CNP (≥0.01 nM) suppressed basal NPo (BNP: 1.00 versus 0.56 ± 0.09 at 10 nM, P < 0.001; CNP: 1.0 versus 0.45 ± 0.16, at 0.01 nM, P < 0.05) and also abolished the pinacidil-activated current at concentrations ≥10 nM. C-ANF (≥10 nM) enhanced KATP activity (1.00 versus 3.85 ± 1.13, at 100 nM, P < 0.05). The cGMP analog 8Br-cGMP 10 nM dampened the pinacidil-activated current (2.92 ± 0.60 versus 1.53 ± 0.32; P < 0.05). Natriuretic peptides modulate sKATP current in ventricular cardiomyocytes. This may be at least partially associated with their ability to augment intracellular cGMP concentrations via NPR-A/B, or their ability to bind NPR-C with high affinity. Although the mechanism of modulation requires elucidation, these preliminary data give new insights into the relationship between natriuretic peptide signaling and sKATP in the myocardium.
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Affiliation(s)
- Dwaine S Burley
- Cardiff School of Pharmacy and Pharmaceutical Sciences, Cardiff University, King Edward VII Avenue, Cardiff, CF10 3NB, UK,
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Coetzee WA. Multiplicity of effectors of the cardioprotective agent, diazoxide. Pharmacol Ther 2013; 140:167-75. [PMID: 23792087 DOI: 10.1016/j.pharmthera.2013.06.007] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Accepted: 06/11/2013] [Indexed: 02/02/2023]
Abstract
Diazoxide has been identified over the past 50years to have a number of physiological effects, including lowering the blood pressure and rectifying hypoglycemia. Today it is used clinically to treat these conditions. More recently, another important mode of action emerged: diazoxide has powerful protective properties against cardiac ischemia. The heart has intrinsic protective mechanisms against ischemia injury; one of which is ischemic preconditioning. Diazoxide mimics ischemic preconditioning. The purpose of this treatise is to review the literature in an attempt to identify the many effectors of diazoxide and discuss how they may contribute to diazoxide's cardioprotective properties. Particular emphasis is placed on the concentration ranges in which diazoxide affects its different targets and how this compares with the concentrations commonly used to study cardioprotection. It is concluded that diazoxide may have several potential effectors that may potentially contribute to cardioprotection, including KATP channels in the pancreas, smooth muscle, endothelium, neurons and the mitochondrial inner membrane. Diazoxide may also affect other ion channels and ATPases and may directly regulate mitochondrial energetics. It is possible that the success of diazoxide lies in this promiscuity and that the compound acts to rebalance multiple physiological processes during cardiac ischemia.
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Affiliation(s)
- William A Coetzee
- Department of Pediatrics, NYU School of Medicine, New York, NY 10016, United States; Department of Physiology & Neuroscience, NYU School of Medicine, New York, NY 10016, United States; Department of Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, NY 10016, United States.
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The KCNJ8-S422L variant previously associated with J-wave syndromes is found at an increased frequency in Ashkenazi Jews. Eur J Hum Genet 2013; 22:94-8. [PMID: 23632791 DOI: 10.1038/ejhg.2013.78] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Revised: 01/11/2013] [Accepted: 03/27/2013] [Indexed: 02/03/2023] Open
Abstract
J-wave syndromes have been associated with increased risk of ventricular fibrillation and sudden cardiac death. Previous studies have identified the KCNJ8-S422L variant in heterozygous form in individuals with J-wave syndromes. Its absence in over 1500 controls, coupled with in vitro analysis, have led to the conclusion that S422L is pathogenic. We previously performed whole-genome sequencing in a family quartet of Ashkenazi Jewish decent with no history of J-wave syndrome. Re-examination of these data reveals that both parents are heterozygous for the S422L variant, while the 12-year old son carries two copies--thus representing the first reported case of a S422L homozygote. In order to examine whether the S422L mutation might segregate at appreciable frequencies in specific populations, we genotyped the variant in a panel consisting of 722 individuals from 22 European, Middle Eastern non-Jewish, Ashkenazi Jewish, and non-Ashkenazi Jewish populations. We found that the S422L allele was at a significantly higher frequency in Ashkenazi Jews (~4%) compared with other populations in our survey, which have frequencies <0.25%. We also performed ECGs in both male members of the family quartet. The homozygous boy demonstrated no clinically significant ECG abnormalities, while the heterozygous father presented with a subtle J-wave point elevation. Our results suggest that either (a) previous studies implicating S422L as pathogenic for J-wave syndromes failed to appropriately account for European population structure and the variant is likely benign, or (b) Ashkenazi Jews may be at significantly increased risk of J-wave syndromes and ultimately sudden cardiac death.
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Wu AZY, Loh SH, Cheng TH, Lu HH, Lin CI. Antiarrhythmic effects of (-)-epicatechin-3-gallate, a novel sodium channel agonist in cultured neonatal rat ventricular myocytes. Biochem Pharmacol 2012; 85:69-80. [PMID: 23116965 DOI: 10.1016/j.bcp.2012.10.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2012] [Revised: 09/24/2012] [Accepted: 10/01/2012] [Indexed: 02/08/2023]
Abstract
(-)-Epicatechin-3-gallate (ECG), a polyphenol extracted from green tea, has been proposed as an effective compound for improving cardiac contractility. However, the therapeutic potential of ECG on the treatment of arrhythmia remains unknown. We investigated the direct actions of ECG on the modulation of ion currents and cardiac cell excitability in the primary culture of neonatal rat ventricular myocyte (NRVM), which is considered a hypertrophic model for analysis of myocardial arrhythmias. By using the whole-cell patch-clamp configurations, we found ECG enhanced the slowly inactivating component of voltage-gated Na(+) currents (I(Na)) in a concentration-dependent manner (0.1-100 μM) with an EC(50) value of 3.8 μM. ECG not only shifted the current-voltage relationship of peak I(Na) to the hyperpolarizing direction but also accelerated I(Na) recovery kinetics. Working at a concentration level of I(Na) enhancement, ECG has no notable effect on voltage-gated K(+) currents and L-type Ca(2+) currents. With culture time increment, the firing rate of spontaneous action potential (sAP) in NRVMs was gradually decreased until spontaneous early after-depolarization (EAD) was observed after about one week culture. ECG increased the firing rate of normal sAP about two-fold without waveform alteration. Interestingly, the bradycardia-dependent EAD could be significantly restored by ECG in fast firing rate to normal sAP waveform. The expression of dominant cardiac sodium channel subunit, Nav1.5, was consistently detected throughout the culture periods. Our results reveal how ECG, the novel I(Na) agonist, may act as a promising candidate in clinical applications on cardiac arrhythmias.
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Affiliation(s)
- Adonis Zhi-Yang Wu
- Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan, ROC
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Barajas-Martínez H, Hu D, Ferrer T, Onetti CG, Wu Y, Burashnikov E, Boyle M, Surman T, Urrutia J, Veltmann C, Schimpf R, Borggrefe M, Wolpert C, Ibrahim BB, Sánchez-Chapula JA, Winters S, Haïssaguerre M, Antzelevitch C. Molecular genetic and functional association of Brugada and early repolarization syndromes with S422L missense mutation in KCNJ8. Heart Rhythm 2011; 9:548-55. [PMID: 22056721 DOI: 10.1016/j.hrthm.2011.10.035] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/25/2011] [Accepted: 10/30/2011] [Indexed: 12/18/2022]
Abstract
BACKGROUND Adenosine triphosphate (ATP)-sensitive potassium cardiac channels consist of inward-rectifying channel subunits Kir6.1 or Kir6.2 (encoded by KCNJ8 or KCNJ11) and the sulfonylurea receptor subunits SUR2A (encoded by ABCC9). OBJECTIVE To examine the association of mutations in KCNJ8 with Brugada syndrome (BrS) and early repolarization syndrome (ERS) and to elucidate the mechanism underlying the gain of function of ATP-sensitive potassium channel current. METHODS Direct sequencing of KCNJ8 and other candidate genes was performed on 204 BrS and ERS probands and family members. Whole-cell and inside-out patch-clamp methods were used to study mutated channels expressed in TSA201 cells. RESULTS The same missense mutation, p.Ser422Leu (c.1265C>T) in KCNJ8, was identified in 3 BrS and 1 ERS probands but was absent in 430 alleles from ethnically matched healthy controls. Additional genetic variants included CACNB2b-D601E. Whole-cell patch-clamp studies showed a 2-fold gain of function of glibenclamide-sensitive ATP-sensitive potassium channel current when KCNJ8-S422L was coexpressed with SUR2A-wild type. Inside-out patch-clamp evaluation yielded a significantly greater half maximal inhibitory concentration for ATP in the mutant channels (785.5 ± 2 vs 38.4 ± 3 μM; n = 5; P <.01), pointing to incomplete closing of the ATP-sensitive potassium channels under normoxic conditions. Patients with a CACNB2b-D601E polymorphism displayed longer QT/corrected QT intervals, likely owing to their effect to induce an increase in L-type calcium channel current (I(Ca-L)). CONCLUSIONS Our results support the hypothesis that KCNJ8 is a susceptibility gene for BrS and ERS and point to S422L as a possible hotspot mutation. Our findings suggest that the S422L-induced gain of function in ATP-sensitive potassium channel current is due to reduced sensitivity to intracellular ATP.
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Affiliation(s)
- Hector Barajas-Martínez
- Molecular Genetics Department, Masonic Medical Research Laboratory, Utica, New York 13501, USA
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Chen BS, Wu SN. Functional role of the activity of ATP-sensitive potassium channels in electrical behavior of hippocampal neurons: Experimental and theoretical studies. J Theor Biol 2011; 272:16-25. [DOI: 10.1016/j.jtbi.2010.12.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2010] [Revised: 10/13/2010] [Accepted: 12/01/2010] [Indexed: 11/17/2022]
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Antzelevitch C, Barajas-Martinez H. A gain-of-function I(K-ATP) mutation and its role in sudden cardiac death associated with J-wave syndromes. Heart Rhythm 2010; 7:1472-4. [PMID: 20736095 PMCID: PMC2946491 DOI: 10.1016/j.hrthm.2010.07.027] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Indexed: 02/07/2023]
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Medeiros-Domingo A, Tan BH, Crotti L, Tester DJ, Eckhardt L, Cuoretti A, Kroboth SL, Song C, Zhou Q, Kopp D, Schwartz PJ, Makielski JC, Ackerman MJ. Gain-of-function mutation S422L in the KCNJ8-encoded cardiac K(ATP) channel Kir6.1 as a pathogenic substrate for J-wave syndromes. Heart Rhythm 2010; 7:1466-71. [PMID: 20558321 DOI: 10.1016/j.hrthm.2010.06.016] [Citation(s) in RCA: 190] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/07/2010] [Accepted: 06/09/2010] [Indexed: 02/07/2023]
Abstract
BACKGROUND J-wave syndromes have emerged conceptually to encompass the pleiotropic expression of J-point abnormalities including Brugada syndrome (BrS) and early repolarization syndrome (ERS). KCNJ8, which encodes the cardiac K(ATP) Kir6.1 channel, recently has been implicated in ERS following identification of the functionally uncharacterized missense mutation S422L. OBJECTIVE The purpose of this study was to further explore KCNJ8 as a novel susceptibility gene for J-wave syndromes. METHODS Using polymerase chain reaction, denaturing high-performance liquid chromatography, and direct DNA sequencing, comprehensive open reading frame/splice site mutational analysis of KCNJ8 was performed in 101 unrelated patients with J-wave syndromes, including 87 with BrS and 14 with ERS. Six hundred healthy individuals were examined to assess the allelic frequency for all variants detected. KCNJ8 mutation(s) was engineered by site-directed mutagenesis and coexpressed heterologously with SUR2A in COS-1 cells. Ion currents were recorded using whole-cell configuration of the patch-clamp technique. RESULTS One BrS case and one ERS case hosted the identical missense mutation S422L, which was reported previously. KCNJ8-S422L involves a highly conserved residue and was absent in 1,200 reference alleles. Both cases were negative for mutations in all known BrS and ERS susceptibility genes. K(ATP) current of the Kir6.1-S422L mutation was increased significantly over the voltage range from 0 to 40 mV compared to Kir6.1-WT channels (n = 16-21; P <.05). CONCLUSION These findings further implicate KCNJ8 as a novel J-wave syndrome susceptibility gene and a marked gain of function in the cardiac K(ATP) Kir6.1 channel secondary to KCNJ8-S422L as a novel pathogenic mechanism for the phenotypic expression of both BrS and ERS.
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Affiliation(s)
- Argelia Medeiros-Domingo
- Department of Medicine (Division of Cardiovascular Diseases), Windland Smith Rice Sudden Death Genomics Laboratory, Mayo Clinic, Rochester, Minnesota 55905, USA
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Tricarico D, Mele A, Camerino GM, Bottinelli R, Brocca L, Frigeri A, Svelto M, George AL, Camerino DC. The KATP channel is a molecular sensor of atrophy in skeletal muscle. J Physiol 2010; 588:773-84. [PMID: 20064856 DOI: 10.1113/jphysiol.2009.185835] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The involvement of ATP-sensitive K(+) (K(ATP)) channels in the atrophy of slow-twitch (MHC-I) soleus (SOL) and fast-twitch (MHC-IIa) flexor digitorum brevis (FDB) muscles was investigated in vivo in 14-day-hindlimb-unloaded (14-HU) rats, an animal model of disuse, and in vitro in drug-induced muscle atrophy. Patch-clamp and gene expression experiments were performed in combination with measurements of fibre diameters used as an index of atrophy, and with MHC labelling in 14-HU rats and controls. A down-regulation of K(ATP) channel subunits Kir6.2, SUR1 and SUR2B with marked atrophy and incomplete phenotype transition were observed in SOL of 14-HU rats. The observed changes in K(ATP) currents were well correlated with changes in fibre diameters and SUR1 expression, as well as with MHC-IIa expression. Half of the SOL fibres of 14-HU rats had reduced diameter and K(ATP) currents and were labelled by MHC-I antibodies. Non-atrophic fibres were labelled by MHC-IIa (22%) antibodies and had enhanced K(ATP) currents, or were labelled by MHC-I (28%) antibodies but had normal current. FDB was not affected in 14-HU rats and this is related to the high expression/activity of Kir6.2/SUR1 subunits characterizing this muscle phenotype. The long-term incubation of the control muscles in vitro with the K(ATP) channel blocker glibenclamide (10(6)m) reduced the K(ATP) currents with atrophy and these effects were prevented by the K(ATP) channel opener diazoxide (10(4)m). The in vivo down-regulation of SUR1, and possibly of Kir6.2 and SUR2B, or their in vitro pharmacological blockade activates atrophic signalling in skeletal muscle. All these findings suggest a new role for the K(ATP) channel as a molecular sensor of atrophy.
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Affiliation(s)
- Domenico Tricarico
- Pharmacobiology Department, Faculty of Pharmacy, University of Bari, Via Orabona No. 4, 70120 Bari, Italy.
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