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Two-Pore-Domain Potassium (K 2P-) Channels: Cardiac Expression Patterns and Disease-Specific Remodelling Processes. Cells 2021; 10:cells10112914. [PMID: 34831137 PMCID: PMC8616229 DOI: 10.3390/cells10112914] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 10/18/2021] [Accepted: 10/22/2021] [Indexed: 12/23/2022] Open
Abstract
Two-pore-domain potassium (K2P-) channels conduct outward K+ currents that maintain the resting membrane potential and modulate action potential repolarization. Members of the K2P channel family are widely expressed among different human cell types and organs where they were shown to regulate important physiological processes. Their functional activity is controlled by a broad variety of different stimuli, like pH level, temperature, and mechanical stress but also by the presence of lipids or pharmacological agents. In patients suffering from cardiovascular diseases, alterations in K2P-channel expression and function have been observed, suggesting functional significance and a potential therapeutic role of these ion channels. For example, upregulation of atrial specific K2P3.1 (TASK-1) currents in atrial fibrillation (AF) patients was shown to contribute to atrial action potential duration shortening, a key feature of AF-associated atrial electrical remodelling. Therefore, targeting K2P3.1 (TASK-1) channels might constitute an intriguing strategy for AF treatment. Further, mechanoactive K2P2.1 (TREK-1) currents have been implicated in the development of cardiac hypertrophy, cardiac fibrosis and heart failure. Cardiovascular expression of other K2P channels has been described, functional evidence in cardiac tissue however remains sparse. In the present review, expression, function, and regulation of cardiovascular K2P channels are summarized and compared among different species. Remodelling patterns, observed in disease models are discussed and compared to findings from clinical patients to assess the therapeutic potential of K2P channels.
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Li XL, Tang CY, Wang S, Zhao M, Wang XF, Li TF, Qi XL, Luan GM, Guan YG. Regulation of TWIK-related K + channel 1 in the anterior hippocampus of patients with temporal lobe epilepsy with comorbid depression. Epilepsy Behav 2021; 121:108045. [PMID: 34116339 DOI: 10.1016/j.yebeh.2021.108045] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/27/2021] [Revised: 04/11/2021] [Accepted: 04/30/2021] [Indexed: 02/08/2023]
Abstract
Epilepsy with comorbid depression has recently attracted increasing attention. Temporal lobe epilepsy (TLE) may represent an increased risk of developing depression, especially if the seizures do not generalize. The two-pore domain potassium channel-TWIK-related K+ channel (TREK-1) plays important roles in both epilepsy and depression. However, the changes in its expression in patients with epilepsy with comorbid depression remain unclear. In the present study, we analyzed depressive symptoms using neuropsychiatric scales in forty-two patients with drug-resistant TLE, who also underwent EEG in waking and sleeping states, as well as 3.0 T brain MRI. We tested for TREK-1 positive neurons and microglial cells in the anterior hippocampi of patients with drug-resistant TLE with and without comorbid depression (n=5/group). Approximately 31% of patients with TLE had comorbid depression (13/42). Meanwhile, the patients who had hippocampal sclerosis had much higher scores on the depression rating scale. The results indicated the contribution of hippocampal sclerosis to the development of depression. Immunostaining of TREK-1 channels was observed in neurons and glia in the anterior hippocampus. Increased immunoreactivity of TREK-1 neurons was observed in the hippocampi of patients with TLE with comorbid depression compared with nondepressed patients with TLE. TREK-1 was expressed in almost all microglia. Curiously, more activated TREK-1-positive microglia were observed in patients with TLE with depression than in those without depression. The results suggested that a change in TREK-1 immunoreactivity was involved, at least partly, in the development of depression as a comorbidity of TLE. Imbalance of the TREK-1 channel may be a potential target for the treatment of patients with epilepsy with comorbid depression.
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Affiliation(s)
- Xiao-Li Li
- Department of Neurology, Affiliated ZhongDa Hospital, Southeast University, Nanjing, China; Department of Neurosurgery, Sanbo Brain Hospital, Capital Medical University, Beijing, China
| | - Chong-Yang Tang
- Department of Neurosurgery, Sanbo Brain Hospital, Capital Medical University, Beijing, China
| | - Shu Wang
- Department of Neurosurgery, Sanbo Brain Hospital, Capital Medical University, Beijing, China
| | - Meng Zhao
- Department of Neurosurgery, Sanbo Brain Hospital, Capital Medical University, Beijing, China
| | - Xiong-Fei Wang
- Department of Neurosurgery, Sanbo Brain Hospital, Capital Medical University, Beijing, China
| | - Tian-Fu Li
- Department of Neurology, Sanbo Brain Hospital, Capital Medical University, Beijing, China; Beijing Key Laboratory of Epilepsy, Beijing, China; Center of Epilepsy, Beijing Institute of Brain Disorders, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing, China
| | - Xue-Ling Qi
- Department of Pathology, Sanbo Brain Hospital, Capital Medical University, Beijing, China
| | - Guo-Ming Luan
- Department of Neurosurgery, Sanbo Brain Hospital, Capital Medical University, Beijing, China; Beijing Key Laboratory of Epilepsy, Beijing, China; Center of Epilepsy, Beijing Institute of Brain Disorders, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing, China.
| | - Yu-Guang Guan
- Department of Neurosurgery, Sanbo Brain Hospital, Capital Medical University, Beijing, China; Beijing Key Laboratory of Epilepsy, Beijing, China; Center of Epilepsy, Beijing Institute of Brain Disorders, Collaborative Innovation Center for Brain Disorders, Capital Medical University, Beijing, China.
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Abstract
PURPOSE OF REVIEW Caffeine is the most widely consumed central nervous stimulant. For people with epilepsy, it is often unclear whether drinking coffee carries a risk of triggering seizures. RECENT FINDINGS The relationship between caffeine, seizures, epilepsy, and anti-seizure drugs is not fully understood. Clinical studies are scarce. In animal models, caffeine can increase seizure susceptibility but can also protect from seizures. Effects seem dose-dependent and are influenced by the duration of intake and the developmental stage at which caffeine exposure started. Caffeine reduces the efficacy of several anti-seizure medications, especially topiramate. It is unclear how these findings, mainly from animal studies, can be translated to the clinical condition. At present, there is no evidence to advise people with epilepsy against the use or overuse of caffeine. Until clinical studies suggest otherwise, caffeine intake should be considered as a factor in achieving and maintaining seizure control in epilepsy.
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Lamas JA, Fernández-Fernández D. Tandem pore TWIK-related potassium channels and neuroprotection. Neural Regen Res 2019; 14:1293-1308. [PMID: 30964046 PMCID: PMC6524494 DOI: 10.4103/1673-5374.253506] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
TWIK-related potassium channels (TREK) belong to a subfamily of the two-pore domain potassium channels family with three members, TREK1, TREK2 and TWIK-related arachidonic acid-activated potassium channels. The two-pore domain potassium channels is the last big family of channels being discovered, therefore it is not surprising that most of the information we know about TREK channels predominantly comes from the study of heterologously expressed channels. Notwithstanding, in this review we pay special attention to the limited amount of information available on native TREK-like channels and real neurons in relation to neuroprotection. Mainly we focus on the role of free fatty acids, lysophospholipids and other neuroprotective agents like riluzole in the modulation of TREK channels, emphasizing on how important this modulation may be for the development of new therapies against neuropathic pain, depression, schizophrenia, epilepsy, ischemia and cardiac complications.
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Affiliation(s)
- J Antonio Lamas
- Laboratory of Neuroscience, Biomedical Research Center (CINBIO), University of Vigo, Vigo, Galicia, Spain
| | - Diego Fernández-Fernández
- Laboratory of Neuroscience, Biomedical Research Center (CINBIO), University of Vigo, Vigo, Galicia, Spain
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van Koert RR, Bauer PR, Schuitema I, Sander JW, Visser GH. Caffeine and seizures: A systematic review and quantitative analysis. Epilepsy Behav 2018; 80:37-47. [PMID: 29414557 DOI: 10.1016/j.yebeh.2017.11.003] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2017] [Revised: 10/31/2017] [Accepted: 11/01/2017] [Indexed: 01/30/2023]
Abstract
PURPOSE Caffeine is the most commonly used central nervous system (CNS) stimulant. The relationship between caffeine, seizures, epilepsy, and antiepileptic drugs (AEDs) is complex and not fully understood. Case reports suggest that caffeine triggers seizures in susceptible people. Our systematic review reports on the relationship between caffeine, seizures, and drugs in animal and human studies. Quantitative analyses were also done on animal studies regarding the effects of caffeine on AEDs. METHODS PubMed was searched for studies assessing the effects of caffeine on seizure susceptibility, epilepsy, and drug interactions in people and in animal models. To quantify the interaction between AEDs and caffeine, the data of six animal studies were pooled and analyzed using a general linear model univariate analysis or One-way Analysis of Variance (ANOVA). RESULTS In total, 442 items were identified from which we included 105 studies. Caffeine can increase seizure susceptibility and protect from seizures, depending on the dose, administration type (chronic or acute), and the developmental stage at which caffeine exposure started. In animal studies, caffeine decreased the antiepileptic potency of some drugs; this effect was strongest in topiramate. CONCLUSION Preclinical studies suggest that caffeine increases seizure susceptibility. In some cases, chronic use of caffeine may protect against seizures. Caffeine lowers the efficacy of several drugs, especially topiramate. It is unclear how these findings in models can be translated to the clinical condition. Until clinical studies suggest otherwise, caffeine intake should be considered as a factor in achieving and maintaining seizure control in epilepsy.
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Affiliation(s)
- Rick R van Koert
- Health, Medical and Neuropsychology Unit, Institute of Psychology, Leiden University, Leiden, The Netherlands
| | - Prisca R Bauer
- Stichting Epilepsie Instellingen Nederland (SEIN), Heemstede, The Netherlands; NIHR University College London Hospitals Biomedical Research Centre, UCL Institute of Neurology, Queen Square, London WC1N 3BG, UK
| | - Ilse Schuitema
- Health, Medical and Neuropsychology Unit, Institute of Psychology, Leiden University, Leiden, The Netherlands
| | - Josemir W Sander
- Stichting Epilepsie Instellingen Nederland (SEIN), Heemstede, The Netherlands; NIHR University College London Hospitals Biomedical Research Centre, UCL Institute of Neurology, Queen Square, London WC1N 3BG, UK; Chalfont Centre for Epilepsy, Chalfont St Peter, UK.
| | - Gerhard H Visser
- Stichting Epilepsie Instellingen Nederland (SEIN), Heemstede, The Netherlands
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Viswanath ANI, Jung SY, Hwang EM, Park KD, Lim SM, Min SJ, Cho YS, Pae AN. Identification of the firstin silico-designed TREK1 antagonists that block channel currents dose dependently. Chem Biol Drug Des 2016; 88:807-819. [DOI: 10.1111/cbdd.12810] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2015] [Revised: 05/03/2016] [Accepted: 06/18/2016] [Indexed: 02/01/2023]
Affiliation(s)
- Ambily Nath Indu Viswanath
- Convergence Research Center for Diagnosis, Treatment and Care System of Dementia; Korea Institute of Science and Technology; Seoul Korea
- Department of Biological Chemistry; Korea University of Science and Technology; Daejeon Korea
| | - Seo Yun Jung
- Convergence Research Center for Diagnosis, Treatment and Care System of Dementia; Korea Institute of Science and Technology; Seoul Korea
| | - Eun Mi Hwang
- Department of Biological Chemistry; Korea University of Science and Technology; Daejeon Korea
- Center for Functional Connectomics; Korea Institute of Science and Technology; Seoul Korea
| | - Ki Duk Park
- Convergence Research Center for Diagnosis, Treatment and Care System of Dementia; Korea Institute of Science and Technology; Seoul Korea
- Department of Biological Chemistry; Korea University of Science and Technology; Daejeon Korea
| | - Sang Min Lim
- Center for Neuro-Medicine; Korea Institute of Science and Technology; Seoul Korea
| | - Sun-Joon Min
- Department of Applied Chemistry; Hanyang University ERICA Campus; Sangnok-gu, Ansan Gyeonggi-do Korea
| | - Yong Seo Cho
- Center for Neuro-Medicine; Korea Institute of Science and Technology; Seoul Korea
| | - Ae Nim Pae
- Convergence Research Center for Diagnosis, Treatment and Care System of Dementia; Korea Institute of Science and Technology; Seoul Korea
- Department of Biological Chemistry; Korea University of Science and Technology; Daejeon Korea
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Bista P, Cerina M, Ehling P, Leist M, Pape HC, Meuth SG, Budde T. The role of two-pore-domain background K⁺ (K₂p) channels in the thalamus. Pflugers Arch 2014; 467:895-905. [PMID: 25346156 DOI: 10.1007/s00424-014-1632-x] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2014] [Revised: 10/09/2014] [Accepted: 10/12/2014] [Indexed: 12/15/2022]
Abstract
The thalamocortical system is characterized by two fundamentally different activity states, namely synchronized burst firing and tonic action potential generation, which mainly occur during the behavioral states of sleep and wakefulness, respectively. The switch between the two firing modes is crucially governed by the bidirectional modulation of members of the K2P channel family, namely tandem of P domains in a weakly inward rectifying K(+) (TWIK)-related acid-sensitive K(+) (TASK) and TWIK-related K(+) (TREK) channels, in thalamocortical relay (TC) neurons. Several physicochemical stimuli including neurotransmitters, protons, di- and multivalent cations as well as clinically used drugs have been shown to modulate K2P channels in these cells. With respect to modulation of these channels by G-protein-coupled receptors, PLCβ plays a unique role with both substrate breakdown and product synthesis exerting important functions. While the degradation of PIP2 leads to the closure of TREK channels, the production of DAG induces the inhibition of TASK channels. Therefore, TASK and TREK channels were found to be central elements in the control of thalamic activity modes. Since research has yet focused on identifying the muscarinic pathway underling the modulation of TASK and TREK channels in TC neurons, future studies should address other thalamic cell types and members of the K2P channel family.
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Affiliation(s)
- Pawan Bista
- Institut für Physiologie I, Westfälische Wilhelms-Universität, Robert-Koch-Str. 27a, 48149, Münster, Germany
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Panaitescu B, Kuribayashi J, Ruangkittisakul A, Leung V, Iizuka M, Ballanyi K. Methylxanthines do not affect rhythmogenic preBötC inspiratory network activity but impair bursting of preBötC-driven motoneurons. Neuroscience 2013; 255:158-76. [DOI: 10.1016/j.neuroscience.2013.09.058] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Revised: 09/26/2013] [Accepted: 09/27/2013] [Indexed: 01/31/2023]
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Shin HJ, Ryu JH, Kim ST, Zuo Z, Do SH. Caffeine-induced inhibition of the activity of glutamate transporter type 3 expressed in Xenopus oocytes. Toxicol Lett 2013; 217:143-8. [DOI: 10.1016/j.toxlet.2012.12.007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Revised: 12/10/2012] [Accepted: 12/10/2012] [Indexed: 10/27/2022]
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Abstract
Clinical evidence, in particular the wide use of theophylline as a bronchodilator, suggests that methylxanthines can cause seizures in patients without known underlying epilepsy. Theophylline is also known to be an added risk factor for seizure exacerbation in patients with epilepsy. The proconvulsant activity of methylxanthines can best be explained by their antagonizing the brain's own anticonvulsant adenosine. Recent evidence suggests that adenosine dysfunction is a pathological hallmark of epilepsy contributing to seizure generation and seizure spread. Conversely, adenosine augmentation therapies are effective in seizure suppression and prevention, whereas adenosine receptor antagonists such as methylxanthines generally exacerbate seizures. The impact of the methylxanthines caffeine and theophylline on seizures and excitotoxicity depends on timing, dose, and acute versus chronic use. New findings suggest a role of free radicals in theophylline-induced seizures, and adenosine-independent mechanisms for seizure generation have been proposed.
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Affiliation(s)
- Detlev Boison
- R.S. Dow Neurobiology Laboratories, Legacy Research, Portland, OR 97232, USA
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11
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Ozbakis-Dengiz G, Bakirci A. Anticonvulsant and hypnotic effects of amiodarone. J Zhejiang Univ Sci B 2009; 10:317-22. [PMID: 19353751 DOI: 10.1631/jzus.b0820316] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Amiodarone hydrochloride is a potent anti-arrhythmic agent, known as a multiple ion-channel blocker in the heart. Although it has been detected in the rat brain, there are no data related to its central nervous system (CNS) effects. In this study, we evaluated anticonvulsant and hypnotic effects of amiodarone. Convulsions were induced by phentylenetetrazole (PTZ) (100 mg/kg) or caffeine (300 mg/kg) in mice. In both models, amiodarone prolonged both latency period and time to death, and acted as an anticonvulsant drug. It was found to be more effective in the PTZ model than in the caffeine model; none of the animals treated with 150 mg/kg dose amiodarone had died in the PTZ model. For hypnotic effect, sleeping was induced with pentobarbital (35 mg/kg) in rats. Amiodarone dose-dependently increased the sleeping time (677.7%-725.9%). In the sleeping test, all rats in 200 mg/kg amiodarone group died. In conclusion, anticonvulsant and hypnotic effects of amiodarone have shown the depressant effects on CNS. These effects may be dependent on its pharmacological properties.
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Affiliation(s)
- Gunnur Ozbakis-Dengiz
- Department of Pharmacology, Medical Faculty, Karaelmas University, 67 600 Zonguldak, Turkey.
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Cohen A, Ben-Abu Y, Hen S, Zilberberg N. A Novel Mechanism for Human K2P2.1 Channel Gating. J Biol Chem 2008; 283:19448-55. [DOI: 10.1074/jbc.m801273200] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
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Hwang SJ, O'Kane N, Singer C, Ward SM, Sanders KM, Koh SD. Block of inhibitory junction potentials and TREK-1 channels in murine colon by Ca2+ store-active drugs. J Physiol 2008; 586:1169-84. [PMID: 18187470 DOI: 10.1113/jphysiol.2007.148718] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Post-junctional enteric inhibitory responses are composed of at least two components attributed to the release of a purine and nitric oxide (NO). The nitrergic component is characterized by membrane potential hyperpolarization; however, the conductances involved and the role of Ca(2+) stores in regulating these conductances are controversial. Conventional microelectrode recordings were performed in intact muscle strips and whole-cell voltage clamp experiments were performed on freshly dispersed cells and COS7 cells stably transfected with TREK-1 channels. Here we show that several Ca(2+) store-active compounds, including caffeine, ryanodine, and cyclopiazonic acid, reduce inhibitory junction potentials and responses to sodium nitroprusside in murine colonic muscles. We previously proposed that two-pore K(+) channels of the TREK family mediate a portion of the hyperpolarization response to NO in colonic muscles. We tested the effects of Ca(2+) store-active drugs in COS cells expressing murine TREK-1 channels and found these compounds block TREK-1 currents. These effects were greatly attenuated by dialysing cells with protein kinase A inhibitory peptide (PKAI). Caffeine also blocked stretch-dependent K(+) (SDK) channels, thought to be due to expression of TREK channels, in colonic myocytes, but these effects were not apparent in excised patches. Taken together our data show that Ca(2+) store-active compounds inhibit TREK-1 channels, native SDK channels, and nitrergic inhibitory junction potentials. These effects appear to be due, in part, to the cAMP/PKA stimulatory actions of these drugs and inhibitory effects of TREK channels.
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Affiliation(s)
- Sung Jin Hwang
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, NV 89557, USA
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Liu H, Enyeart JA, Enyeart JJ. Potent Inhibition of Native TREK-1 K+Channels by Selected Dihydropyridine Ca2+Channel Antagonists. J Pharmacol Exp Ther 2007; 323:39-48. [PMID: 17622574 DOI: 10.1124/jpet.107.125245] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Bovine adrenal zona fasciculata (AZF) cells express bTREK-1 background K+ channels that set the resting membrane potential. Whole-cell and single-channel patch-clamp recording were used to compare five Ca2+ channel antagonists with respect to their potency as inhibitors of native bTREK-1 K+ channels. The dihydropyridine (DHP) Ca2+ channel antagonists amlodipine and niguldipine potently and specifically inhibited bTREK-1 with IC50 values of 0.43 and 0.75 microM, respectively. The other Ca2+ channel antagonists, including the DHP nifedipine, the diphenyldiperazine flunarizine, and the cannabinoid anandamide were less potent, with IC50 values of 8.18, 2.48, and 5.07 microM, respectively. Additional studies with the highly prescribed antihypertensive amlodipine showed that inhibition of bTREK-1 by this agent was voltage-independent and specific. At concentrations that produced near complete block of bTREK-1, amlodipine inhibited voltage-gated Kv1.4 K+ and T-type Ca2+ currents in AZF cells by less than 10%. At the single-channel level, amlodipine reduced bTREK-1 open probability without altering the unitary conductance. The results demonstrate that selected DHP L-type Ca2+ channel antagonists potently inhibit native bTREK-1 K+ channels, whereas other Ca2+ channel antagonists also inhibit bTREK-1 at higher concentrations. Collectively, organic Ca2+ channel antagonists make up the most potent class of TREK-1 inhibitors yet described. Because TREK-1 K+ channels are widely expressed in the central nervous and cardiovascular systems, it is possible that some of the therapeutic or toxic effects of frequently prescribed drugs such as amlodipine may be due to their interaction with TREK-1 K+ rather L-type Ca2+ channels.
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Affiliation(s)
- Haiyan Liu
- Department of Neuroscience, 5196 Graves Hall, College of Medicine and Public Health, The Ohio State University, 333 W. 10th Ave., Columbus, OH 43210-1239, USA
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Mao X, Chai Y, Lin YF. Dual regulation of the ATP-sensitive potassium channel by caffeine. Am J Physiol Cell Physiol 2007; 292:C2239-58. [PMID: 17303650 DOI: 10.1152/ajpcell.00326.2006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
ATP-sensitive potassium (K(ATP)) channels couple cellular metabolic status to changes in membrane electrical properties. Caffeine (1,2,7-trimethylxanthine) has been shown to inhibit several ion channels; however, how caffeine regulates K(ATP) channels was not well understood. By performing single-channel recordings in the cell-attached configuration, we found that bath application of caffeine significantly enhanced the currents of Kir6.2/SUR1 channels, a neuronal/pancreatic K(ATP) channel isoform, expressed in transfected human embryonic kidney (HEK)293 cells in a concentration-dependent manner. Application of nonselective and selective phosphodiesterase (PDE) inhibitors led to significant enhancement of Kir6.2/SUR1 channel currents. Moreover, the stimulatory action of caffeine was significantly attenuated by KT5823, a specific PKG inhibitor, and, to a weaker extent, by BAPTA/AM, a membrane-permeable Ca(2+) chelator, but not by H-89, a selective PKA inhibitor. Furthermore, the stimulatory effect was completely abrogated when KT5823 and BAPTA/AM were co-applied with caffeine. In contrast, the activity of Kir6.2/SUR1 channels was decreased rather than increased by caffeine in cell-free inside-out patches, while tetrameric Kir6.2LRKR368/369/370/371AAAA channels were suppressed regardless of patch configurations. Caffeine also enhanced the single-channel currents of recombinant Kir6.2/SUR2B channels, a nonvascular smooth muscle K(ATP) channel isoform, although the increase was smaller. Moreover, bidirectional effects of caffeine were reproduced on the K(ATP) channel present in the Cambridge rat insulinoma G1 (CRI-G1) cell line. Taken together, our data suggest that caffeine exerts dual regulation on the function of K(ATP) channels: an inhibitory regulation that acts directly on Kir6.2 or some closely associated regulatory protein(s), and a sulfonylurea receptor (SUR)-dependent stimulatory regulation that requires cGMP-PKG and intracellular Ca(2+)-dependent signaling.
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Affiliation(s)
- Xia Mao
- Dept. of Physiology, University of California, Davis, CA 95616, USA
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