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Zhi-Gang Huang, Hao-Wen Liu, Zhen-Zhen Yan, Sheng Wang, Lu-Yang Wang, Jiu-Ping Ding
Large-conductance Ca(2+)- and voltage- activated potassium (MaxiK or BK) channels are composed of a pore-forming α subunit (Slo) and four types of auxiliary β subunits or just a pore-forming α subunit. Although multiple N-linked glycosylation sites in the extracellular loop of β subunits have been identified, very little is known about how glycosylation influences the structure and function of BK channels. Using a combination of site-directed mutagenesis, western blot and patch-clamp recordings, we demonstrated that three sites in the extracellular loop of β2 subunit are N-glycosylated (N-X-T/S at N88, N96 and N119)...
October 3, 2016: Channels
Zoltán Pethő, Mark R Tanner, Rajeev B Tajhya, Redwan Huq, Teresina Laragione, Gyorgy Panyi, Pércio S Gulko, Christine Beeton
BACKGROUND: Fibroblast-like synoviocytes (FLS) in rheumatoid arthritis (RA-FLS) contribute to joint inflammation and damage characteristic of the disease. RA-FLS express KCa1.1 (BK, Slo1, MaxiK, KCNMA1) as their major plasma membrane potassium channel. Blocking KCa1.1 reduces the invasive phenotype of RA-FLS and attenuates disease severity in animal models of RA. This channel has therefore emerged as a promising therapeutic target in RA. However, the pore-forming α subunit of KCa1.1 is widely distributed in the body, and blocking it induces severe side effects, thus limiting its value as a therapeutic target...
2016: Arthritis Research & Therapy
H Singh, M Li, L Hall, S Chen, S Sukur, R Lu, A Caputo, A L Meredith, E Stefani, L Toro
Large conductance voltage and calcium-activated potassium (MaxiK) channels are activated by membrane depolarization and elevated cytosolic Ca(2+). In the brain, they localize to neurons and astrocytes, where they play roles such as resetting the membrane potential during an action potential, neurotransmitter release, and neurovascular coupling. MaxiK channels are known to associate with several modulatory proteins and accessory subunits, and each of these interactions can have distinct physiological consequences...
March 11, 2016: Neuroscience
Olaf Strauß, Nadine Reichhart, Nestor Mas Gomez, Claudia Müller
Mutations in the BEST1 gene lead to a variety of retinal degenerations including Best's vitelliforme macular degeneration. The BEST1 gene product, bestrophin-1, is expressed in the retinal pigment epithelium (RPE). It is likely that mutant bestrophin-1 impairs functions of the RPE which support photoreceptor function and will thus lead to retinal degeneration. However, the RPE function which is influenced by bestrophin-1 is so far not identified. Previously we showed that bestrophin-1 interacts with L-type Ca²⁺ channels of the CaV1...
2016: Advances in Experimental Medicine and Biology
Naseem Sunnoqrot, Robert F Reilly
We report a case of hypokalemia resulting from colonic pseudo-obstruction or Ogilvie's syndrome. Colonic pseudo-obstruction is characterized by profuse watery diarrhea that has a low sodium and high potassium concentration. It is seen in a variety of medical and surgical conditions, but its exact cause remains unknown. It is thought to result from an imbalance of sympathetic and parasympathetic input in the distal colon. The diarrhea is secretory and driven by potassium secretion rather than the inhibition of sodium reabsorption or chloride secretion, which are the most common pathophysiologic mechanisms of secretory diarrhea...
May 2015: Case Reports in Nephrology and Dialysis
Jiaqi Tang, Zhoufeng Zhu, Shuixiu Xia, Na Li, Ningjing Chen, Qinqin Gao, Lingjun Li, Xiuwen Zhou, Dawei Li, Xiaolin Zhu, Qing Tu, Weisheng Li, Chonglong Wu, Jiayue Li, Yuan Zhong, Xiang Li, Caiping Mao, Zhice Xu
Hypoxia during pregnancy could affect development of fetuses as well as cardiovascular systems in the offspring. This study was the first to demonstrate the influence and related mechanisms of prenatal hypoxia (PH) on renal interlobar arteries (RIA) in the 5-month-old male rat offspring. Following chronic hypoxia during pregnancy, phenylephrine induced significantly higher pressor responses and greater vasoconstrictions in the offspring. Nitric oxide mediated vessel relaxation was altered in the RIA. Phenylephrine-stimulated free intracellular calcium was significantly higher in the RIA of the PH group...
2015: Scientific Reports
Yonghae Son, Wonjoo Chun, Yong-Tae Ahn, Koanhoi Kim, Chul-Won Lee, Jong-Myoung Kim, Chu Lee, Won G An
Hypertension is a high-risk symptom in atherosclerotic patients, and vascular rigidity is one of the main factors leading to hypertension. β1-Subunit of BKCa channel (KCNMB1; MaxiKβ1) has been reported as a modulator of vascular flexibility. To determine the relationship between atherosclerosis and KCNMB1, we studied some atherogenic factors affecting vascular tone. Blood of atherosclerotic patients shows increased concentration of 7-ketocholesterol (7K), which has been studied as a harmful lipid to blood vessels...
February 13, 2015: Biochemical and Biophysical Research Communications
Andreas Genewsky, Ingmar Jost, Catharina Busch, Christian Huber, Julia Stindl, Christine Skerka, Peter F Zipfel, Bärbel Rohrer, Olaf Strauß
Defective regulation of the alternative pathway of the complement system is believed to contribute to damage of retinal pigment epithelial (RPE) cells in age-related macular degeneration. Thus we investigated the effect of complement activation on the RPE cell membrane by analyzing changes in membrane conductance via patch-clamp techniques and Ca(2+) imaging. Exposure of human ARPE-19 cells to complement-sufficient normal human serum (NHS) (25 %) resulted in a biphasic increase in intracellular free Ca(2+) ([Ca(2+)]i); an initial peak followed by sustained Ca(2+) increase...
October 2015: Pflügers Archiv: European Journal of Physiology
Bo H Bentzen, Søren-Peter Olesen, Lars C B Rønn, Morten Grunnet
The large conductance calcium- and voltage-activated K(+) channel (KCa1.1, BK, MaxiK) is ubiquitously expressed in the body, and holds the ability to integrate changes in intracellular calcium and membrane potential. This makes the BK channel an important negative feedback system linking increases in intracellular calcium to outward hyperpolarizing potassium currents. Consequently, the channel has many important physiological roles including regulation of smooth muscle tone, neurotransmitter release and neuronal excitability...
2014: Frontiers in Physiology
Alex M Dopico, Anna N Bukiya
This mini-review focuses on lipid modulation of BK (MaxiK, BKCa) current by a direct interaction between lipid and the BK subunits and/or their immediate lipid environment. Direct lipid-BK protein interactions have been proposed for fatty and epoxyeicosatrienoic acids, phosphoinositides and cholesterol, evidence for such action being less clear for other lipids. BK α (slo1) subunits are sufficient to support current perturbation by fatty and epoxyeicosatrienoic acids, glycerophospholipids and cholesterol, while distinct BK β subunits seem necessary for current modulation by most steroids...
2014: Frontiers in Physiology
Sarah L Waite, Saurabh V Gandhi, Raheela N Khan, Neil R Chapman
The onset of human parturition is associated with up-regulation of pro-inflammatory cytokines including tumor necrosis factor (TNF) as well as changes in ion flux, principally Ca(2+) and K(+), across the myometrial myocytes membrane. Elevation of intra-cellular Ca(2+) from the sarcoplasmic reticulum opens L-type Ca(2+) channels (LTCCs); in turn this increased calcium level activates MaxiK channels leading to relaxation. While the nature of how this cross-talk is governed remains unclear, our previous work demonstrated that the pro-inflammatory cytokine, TNF, and the histone deacetylase inhibitor, Trichostatin-A (TSA), exerted opposing effects on the expression of the pro-quiescent Gαs gene in human myometrial cells...
2014: Frontiers in Physiology
Georgi V Petkov
The physiological functions of the urinary bladder are to store and periodically expel urine. These tasks are facilitated by the contraction and relaxation of the urinary bladder smooth muscle (UBSM), also known as detrusor smooth muscle, which comprises the bladder wall. The large-conductance voltage- and Ca(2+)-activated K(+) (BK, BKCa, MaxiK, Slo1, or KCa1.1) channel is highly expressed in UBSM and is arguably the most important physiologically relevant K(+) channel that regulates UBSM function. Its significance arises from the fact that the BK channel is the only K(+) channel that is activated by increases in both voltage and intracellular Ca(2+)...
September 15, 2014: American Journal of Physiology. Regulatory, Integrative and Comparative Physiology
Bernhard Nausch, Frederik Rode, Susanne Jørgensen, Antonio Nardi, Mads P G Korsgaard, Charlotte Hougaard, Adrian D Bonev, William D Brown, Tino Dyhring, Dorte Strøbæk, Søren-Peter Olesen, Palle Christophersen, Morten Grunnet, Mark T Nelson, Lars C B Rønn
Large-conductance Ca(2+)-activated K(+) channels (BK, KCa1.1, MaxiK) are important regulators of urinary bladder function and may be an attractive therapeutic target in bladder disorders. In this study, we established a high-throughput fluorometric imaging plate reader-based screening assay for BK channel activators and identified a small-molecule positive modulator, NS19504 (5-[(4-bromophenyl)methyl]-1,3-thiazol-2-amine), which activated the BK channel with an EC50 value of 11.0 ± 1.4 µM. Hit validation was performed using high-throughput electrophysiology (QPatch), and further characterization was achieved in manual whole-cell and inside-out patch-clamp studies in human embryonic kidney 293 cells expressing hBK channels: NS19504 caused distinct activation from a concentration of 0...
September 2014: Journal of Pharmacology and Experimental Therapeutics
Yi Wang, Moses T Tar, Shibo Fu, Arnold Melman, Kelvin P Davies
OBJECTIVES: To investigate the effect of diabetes on urothelial modulation of bladder contractility. METHODS: Bladder strips (urothelium intact or denuded) were prepared from 8-week-old streptozotocin-induced diabetic (n = 19) and non-diabetic control rats (n = 10). The effect of modulators of MaxiK (iberiotoxin and tetraethylammonium) and Kv7 (XE991 and retigabine) potassium channel activity were investigated for their effects on both carbachol-induced force generation and spontaneous contractile activity...
October 2014: International Journal of Urology: Official Journal of the Japanese Urological Association
Jian-Dong Ren, Yong-Jun Xing, Kai-Hua Fan, Bo-Tao Yu, Wei-Hua Jin, Yan Jiang, Li Jing, Xue-Chai Wu, Shi-Hua Wang, Juan Wu, Hua Chen
Increasing evidence has recently demonstrated that soluble heparan sulfate (HS), a degradation product of extracellular matrix produced by elastase, plays a key role in the aggravation of acute pancreatitis (AP) and associated lung injury. However little is known about the detailed mechanism underlying HS-induced inflammatory cascade. Our previous work has provided a valuable clue that a large-conductance K(+) channel (MaxiK) was involved in the HS-stimulated activation of murine macrophages. Here we attempted to ask whether pharmacological inhibition of the MaxiK channel will exert beneficial effects on the treatment of AP and secondary lung injury...
July 2014: International Immunopharmacology
E Sánchez-Pastor, F Andrade, J M Sánchez-Pastor, A Elizalde, M Huerta, A Virgen-Ortiz, X Trujillo, A Rodríguez-Hernández
Cannabinoids are key regulators of vascular tone, some of the mechanisms involved include the activation of cannabinoid receptor types 1 and 2 (CB); the transient receptor potential cation channel, subfamily V, member 1 (TRPV1); and non-(CB(1))/non-CB2 receptors. Here, we used the potent, selective CB(1) agonist arachidonylcyclopropylamide (ACPA) to elucidate the mechanism underlying vascular tone regulation. Immunohistochemistry and confocal microscopy revealed that CB(1) was expressed in smooth muscle and endothelial cells in rat aorta...
April 15, 2014: European Journal of Pharmacology
N Cox, B Toro, L F Pacheco-Otalora, E R Garrido-Sanabria, M M Zarei
Voltage-dependent and calcium-activated K⁺ (MaxiK, BK) channels are widely expressed in many tissues and organs where they play various physiological roles. Here we report discovery of a functional trafficking signal in MaxiK channel accessory β4 subunit that could regulate activity of MaxiK α subunit (hSlo) on the plasma membrane. We demonstrate that β4 is mostly retained within the cell and removal or mutation of β4 trafficking signal significantly enhances its surface expression in HEK293T expression system...
March 17, 2014: Brain Research
Claudia Müller, Néstor Más Gómez, Peter Ruth, Olaf Strauss
Phagocytosis of shed photoreceptor outer segments by the retinal pigment epithelium (RPE) is critical for maintenance of visual function. Because changes in intracellular Ca(2+) regulate phagocytosis, we studied in vitro the impact of different ion channels in addition to mice deficient for Cav1.3 L-type Ca(2+) channels (Ca1.3(-/-)) and maxiK Ca(2+)-dependent K(+) channels (BK(-/-)). The knockdown of Bestrophin-1 protein, a regulator of intracellular Ca(2+) homeostasis, affected phagocytosis in porcine RPE cultures...
May 2014: Cellular Signalling
Lijun Shi, Bailin Liu, Yanyan Zhang, Zhimin Xue, Yujia Liu, Yu Chen
This study was designed to determine the effects of aerobic exercise training on aging-associated selective changes of the function and expression of the large-conductance Ca(2+)-activated K(+) (MaxiK) channels in mesenteric arteries. Male Wistar rats aged 19-21 months were randomly assigned to sedentary (O-SED) and exercise-trained groups (O-EX). Two-month-old rats were used as Young control. Addition of iberiotoxin (10(-8) M) increased the norepinephrine-induced arterial contraction in all three groups, with the greatest enhancement being in Young and the least in O-SED...
December 2014: Journals of Gerontology. Series A, Biological Sciences and Medical Sciences
Jian-Dong Ren, Li Fan, Fu-Zhou Tian, Kai-Hua Fan, Bo-Tao Yu, Wei-Hua Jin, Yong-Hong Tan, Long Cheng
Increasing evidence has demonstrated that Toll-like receptor 4 (TLR4) -mediated systemic inflammatory response syndrome accompanied by multiple organ failure, is one of the most common causes of death in patients with severe acute pancreatitis. Recent reports have revealed that heparan sulphate (HS) proteoglycan, a component of extracellular matrices, potentiates the activation of intracellular pro-inflammatory responses via TLR4, contributing to the aggravation of acute pancreatitis. However, little is known about the participants in the HS/TLR4-mediated inflammatory cascades...
March 2014: Immunology
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