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Fu W, Vasylyev D, Bi Y, Zhang M, Sun G, Khleborodova A, Huang G, Zhao L, Zhou R, Li Y, Liu S, Cai X, He W, Cui M, Zhao X, Hettinghouse A, Good J, Kim E, Strauss E, Leucht P, Schwarzkopf R, Guo EX, Samuels J, Hu W, Attur M, Waxman SG, Liu CJ. Na v1.7 as a chondrocyte regulator and therapeutic target for osteoarthritis. Nature 2024; 625:557-565. [PMID: 38172636 PMCID: PMC10794151 DOI: 10.1038/s41586-023-06888-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Accepted: 11/22/2023] [Indexed: 01/05/2024]
Abstract
Osteoarthritis (OA) is the most common joint disease. Currently there are no effective methods that simultaneously prevent joint degeneration and reduce pain1. Although limited evidence suggests the existence of voltage-gated sodium channels (VGSCs) in chondrocytes2, their expression and function in chondrocytes and in OA remain essentially unknown. Here we identify Nav1.7 as an OA-associated VGSC and demonstrate that human OA chondrocytes express functional Nav1.7 channels, with a density of 0.1 to 0.15 channels per µm2 and 350 to 525 channels per cell. Serial genetic ablation of Nav1.7 in multiple mouse models demonstrates that Nav1.7 expressed in dorsal root ganglia neurons is involved in pain, whereas Nav1.7 in chondrocytes regulates OA progression. Pharmacological blockade of Nav1.7 with selective or clinically used pan-Nav channel blockers significantly ameliorates the progression of structural joint damage, and reduces OA pain behaviour. Mechanistically, Nav1.7 blockers regulate intracellular Ca2+ signalling and the chondrocyte secretome, which in turn affects chondrocyte biology and OA progression. Identification of Nav1.7 as a novel chondrocyte-expressed, OA-associated channel uncovers a dual target for the development of disease-modifying and non-opioid pain relief treatment for OA.
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Affiliation(s)
- Wenyu Fu
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT, USA
| | - Dmytro Vasylyev
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA
- Center for Neuroscience and Regeneration Research, Veterans Affairs Connecticut Healthcare, West Haven, CT, USA
| | - Yufei Bi
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Mingshuang Zhang
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Guodong Sun
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Asya Khleborodova
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Guiwu Huang
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT, USA
| | - Libo Zhao
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT, USA
| | - Renpeng Zhou
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT, USA
| | - Yonggang Li
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT, USA
| | - Shujun Liu
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA
- Center for Neuroscience and Regeneration Research, Veterans Affairs Connecticut Healthcare, West Haven, CT, USA
| | - Xianyi Cai
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Wenjun He
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Min Cui
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Xiangli Zhao
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT, USA
| | - Aubryanna Hettinghouse
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Julia Good
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Ellen Kim
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Eric Strauss
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Philipp Leucht
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Ran Schwarzkopf
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA
| | - Edward X Guo
- Department of Biomedical Engineering, Columbia University, New York, NY, USA
| | - Jonathan Samuels
- Division of Rheumatology, Department of Medicine, New York University Grossman School of Medicine, New York, NY, USA
| | - Wenhuo Hu
- Human Oncology and Pathogenesis Program, Memorial Sloan Kettering Cancer Center, New York, NY, USA
- Marie-Josée and Henry R. Kravis Center for Molecular Oncology, Memorial Sloan Kettering Cancer Center, New York, NY, USA
| | - Mukundan Attur
- Division of Rheumatology, Department of Medicine, New York University Grossman School of Medicine, New York, NY, USA
| | - Stephen G Waxman
- Department of Neurology, Yale School of Medicine, New Haven, CT, USA.
- Center for Neuroscience and Regeneration Research, Veterans Affairs Connecticut Healthcare, West Haven, CT, USA.
| | - Chuan-Ju Liu
- Department of Orthopaedic Surgery, New York University Grossman School of Medicine, New York, NY, USA.
- Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, New Haven, CT, USA.
- Department of Cell Biology, New York University Grossman School of Medicine, New York, NY, USA.
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Zhang F, Wu C, Zhang P, Wang X, Meng P, Tan S, Yuan L, Guo X. Abnormal Level of Manganese, Iron, Iodine, and Selenium in the Hair of Children Living in Kashin-Beck Disease Endemic Areas. Biol Trace Elem Res 2022; 200:4278-4288. [PMID: 34993910 DOI: 10.1007/s12011-021-03031-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/20/2021] [Accepted: 11/13/2021] [Indexed: 11/02/2022]
Abstract
Biological geochemistry is a main suggested cause of Kashin-Beck disease (KBD), due to the absence or excess of elements in the environment. Initially, Se deficiency is regarded as the most key role in the etiology of KBD, and selenium supplementation effectively helps to prevent and control KBD. However, several elements are reported to be relevant to KBD or selenium in succession, which indicated selenium deficiency is not the original etiology of KBD. The study comprehensively analyzed the characteristics of the bio-element profile of KBD and further re-examined the unique role of selenium in etiology. The study measured 14 elements, including sodium, potassium, calcium, phosphorus, magnesium, copper, iron, zinc, selenium, iodine, manganese, lead, arsenic, and mercury, which were detected from hair samples collected from 150 boys. Research participants were separated based on whether they had received any preventative treatment (with and without selenium supplementation). From endemic areas, 30 KBD and 30 healthy children without any preventative treatment were selected alongside 30 KBD and 30 healthy children with selenium supplementation. The participants from endemic areas were then compared to 30 healthy children living in non-endemic areas. Compared to the non-endemic group, the levels of iron and manganese were all significantly higher in the endemic groups and were further elevated in KBD participants (p < 0.05). In contrast, selenium and iodine levels in endemic areas were much lower than those of the control group (p < 0.05). The proportions of selenium excess (p < 0.05) and iodine deficiency (p < 0.05) in endemic groups were significantly lower than participants from non-endemic areas. Meanwhile, excess levels of iron (p < 0.05) and manganese (p < 0.05) were higher in the endemic groups. Moreover, the proportions of Zn/Fe and Se/Mn were found to be significantly lower in endemic area participants than those in the control group (p < 0.05). Three pairs of elements had a correlation coefficient value of more than 0.6: 0.7423 for manganese and calcium, 0.6446 for potassium and sodium, and 0.6272 for manganese and iron. The ratios of Se/Mn and Zn/Fe were associated with a correlation coefficient value of 0.8055. Magnesium, sodium, copper, and iodine levels were meticulously examined using binary regression analysis. This was also used to determine the ratios of Ca/Mg, Ca/P, Zn/Fe, Se/Mn, and Se/I. Thus, the study largely revealed the vital role of manganese, iron, and iodine (in conjunction with selenium) in KBD etiology and pathogenesis. High manganese and iron levels with low selenium and iodine levels were identified as characteristic features of the bio-element profile of KBD. The different element ratios reflect the interaction between several elements. The most significant of these were the proportions of Se/Mn and Zn/Fe, which may be significant in the occurrence and development of KBD.
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Affiliation(s)
- Feng'e Zhang
- School of Public Health, Key Laboratory of Trace Elements and Endemic Diseases, Collaborative Innovation Center of Endemic Diseases and Health Promotion for Silk Road Region of Shaanxi Province, National Health Commission of the People's Republic of China, Health Science Center of Xi'an Jiaotong University, Xi'an, 710061, People's Republic of China
| | - Cuiyan Wu
- School of Public Health, Key Laboratory of Trace Elements and Endemic Diseases, Collaborative Innovation Center of Endemic Diseases and Health Promotion for Silk Road Region of Shaanxi Province, National Health Commission of the People's Republic of China, Health Science Center of Xi'an Jiaotong University, Xi'an, 710061, People's Republic of China
| | - Pan Zhang
- Sichuan Provincial Center for Disease Control and Prevention, Chengdu, 610041, People's Republic of China
| | - Xi Wang
- School of Public Health, Key Laboratory of Trace Elements and Endemic Diseases, Collaborative Innovation Center of Endemic Diseases and Health Promotion for Silk Road Region of Shaanxi Province, National Health Commission of the People's Republic of China, Health Science Center of Xi'an Jiaotong University, Xi'an, 710061, People's Republic of China
| | - Peilin Meng
- School of Public Health, Key Laboratory of Trace Elements and Endemic Diseases, Collaborative Innovation Center of Endemic Diseases and Health Promotion for Silk Road Region of Shaanxi Province, National Health Commission of the People's Republic of China, Health Science Center of Xi'an Jiaotong University, Xi'an, 710061, People's Republic of China
| | - Sijia Tan
- School of Public Health, Key Laboratory of Trace Elements and Endemic Diseases, Collaborative Innovation Center of Endemic Diseases and Health Promotion for Silk Road Region of Shaanxi Province, National Health Commission of the People's Republic of China, Health Science Center of Xi'an Jiaotong University, Xi'an, 710061, People's Republic of China
| | - Linlin Yuan
- School of Public Health, Key Laboratory of Trace Elements and Endemic Diseases, Collaborative Innovation Center of Endemic Diseases and Health Promotion for Silk Road Region of Shaanxi Province, National Health Commission of the People's Republic of China, Health Science Center of Xi'an Jiaotong University, Xi'an, 710061, People's Republic of China
| | - Xiong Guo
- School of Public Health, Key Laboratory of Trace Elements and Endemic Diseases, Collaborative Innovation Center of Endemic Diseases and Health Promotion for Silk Road Region of Shaanxi Province, National Health Commission of the People's Republic of China, Health Science Center of Xi'an Jiaotong University, Xi'an, 710061, People's Republic of China.
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Fischer-Holzhausen S, Yamamoto K, Fjeldstad MP, Maleckar MM. Probing the Putative Role of K ATP Channels and Biological Variability in a Mathematical Model of Chondrocyte Electrophysiology. Bioelectricity 2021. [DOI: 10.1089/bioe.2021.0034] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Affiliation(s)
| | - Kei Yamamoto
- Department of Mathematics, University of Oslo, Oslo, Norway
- Computational Physiology, Simula Research Laboratory, Oslo, Norway
| | | | - Mary M. Maleckar
- Computational Physiology, Simula Research Laboratory, Oslo, Norway
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4
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Dielectrophoresis as a Tool to Reveal the Potential Role of Ion Channels and Early Electrophysiological Changes in Osteoarthritis. MICROMACHINES 2021; 12:mi12080949. [PMID: 34442571 PMCID: PMC8402151 DOI: 10.3390/mi12080949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 07/30/2021] [Accepted: 08/08/2021] [Indexed: 11/16/2022]
Abstract
Diseases such as osteoarthritis (OA) are commonly characterized at the molecular scale by gene expression and subsequent protein production; likewise, the effects of pharmaceutical interventions are typically characterized by the effects of molecular interactions. However, these phenomena are usually preceded by numerous precursor steps, many of which involve significant ion influx or efflux. As a consequence, rapid assessment of cell electrophysiology could play a significant role in unravelling the mechanisms underlying drug interactions and progression of diseases, such as OA. In this study, we used dielectrophoresis (DEP), a technique that allows rapid, label-free determination of the dielectric parameters to assess the role of potassium ions on the dielectric characteristics of chondrocytes, and to investigate the electrophysiological differences between healthy chondrocytes and those from an in vitro arthritic disease model. Our results showed that DEP was able to detect a significant decrease in membrane conductance (6191 ± 738 vs. 8571 ± 1010 S/m2), membrane capacitance (10.3 ± 1.47 vs. 14.5 ± 0.01 mF/m2), and whole cell capacitance (5.4 ± 0.7 vs. 7.5 ± 0.3 pF) following inhibition of potassium channels using 10 mM tetraethyl ammonium, compared to untreated healthy chondrocytes. Moreover, cells from the OA model had a different response to DEP force in comparison to healthy cells; this was seen in terms of both a decreased membrane conductivity (782 S/m2 vs. 1139 S/m2) and a higher whole cell capacitance (9.58 ± 3.4 vs. 3.7 ± 1.3 pF). The results show that DEP offers a high throughput method, capable of detecting changes in membrane electrophysiological properties and differences between disease states.
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5
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Matta C, Lewis R, Fellows C, Diszhazi G, Almassy J, Miosge N, Dixon J, Uribe MC, May S, Poliska S, Barrett-Jolley R, Fodor J, Szentesi P, Hajdú T, Keller-Pinter A, Henslee E, Labeed FH, Hughes MP, Mobasheri A. Transcriptome-based screening of ion channels and transporters in a migratory chondroprogenitor cell line isolated from late-stage osteoarthritic cartilage. J Cell Physiol 2021; 236:7421-7439. [PMID: 34008188 DOI: 10.1002/jcp.30413] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2020] [Revised: 04/28/2021] [Accepted: 05/04/2021] [Indexed: 12/13/2022]
Abstract
Chondrogenic progenitor cells (CPCs) may be used as an alternative source of cells with potentially superior chondrogenic potential compared to mesenchymal stem cells (MSCs), and could be exploited for future regenerative therapies targeting articular cartilage in degenerative diseases such as osteoarthritis (OA). In this study, we hypothesised that CPCs derived from OA cartilage may be characterised by a distinct channelome. First, a global transcriptomic analysis using Affymetrix microarrays was performed. We studied the profiles of those ion channels and transporter families that may be relevant to chondroprogenitor cell physiology. Following validation of the microarray data with quantitative reverse transcription-polymerase chain reaction, we examined the role of calcium-dependent potassium channels in CPCs and observed functional large-conductance calcium-activated potassium (BK) channels involved in the maintenance of the chondroprogenitor phenotype. In line with our very recent results, we found that the KCNMA1 gene was upregulated in CPCs and observed currents that could be attributed to the BK channel. The BK channel inhibitor paxilline significantly inhibited proliferation, increased the expression of the osteogenic transcription factor RUNX2, enhanced the migration parameters, and completely abolished spontaneous Ca2+ events in CPCs. Through characterisation of their channelome we demonstrate that CPCs are a distinct cell population but are highly similar to MSCs in many respects. This study adds key mechanistic data to the in-depth characterisation of CPCs and their phenotype in the context of cartilage regeneration.
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Affiliation(s)
- Csaba Matta
- Department of Anatomy, Histology and Embryology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary.,Department of Veterinary Preclinical Sciences, School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK
| | - Rebecca Lewis
- Department of Veterinary Preclinical Sciences, School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK
| | - Christopher Fellows
- Department of Veterinary Preclinical Sciences, School of Veterinary Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, UK
| | - Gyula Diszhazi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Janos Almassy
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Nicolai Miosge
- Department of Prosthodontics, Tissue Regeneration Work Group, Georg August University, Göttingen, Germany
| | - James Dixon
- Wolfson Centre for Stem Cells, Tissue Engineering and Modelling, Centre of Biomolecular Sciences, School of Pharmacy, University of Nottingham, Nottingham, UK
| | - Marcos C Uribe
- The Nottingham Arabidopsis Stock Centre (NASC), School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, UK
| | - Sean May
- The Nottingham Arabidopsis Stock Centre (NASC), School of Biosciences, University of Nottingham, Sutton Bonington Campus, Loughborough, UK
| | - Szilard Poliska
- Genomic Medicine and Bioinformatic Core Facility, Department of Biochemistry and Molecular Biology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Richard Barrett-Jolley
- Department of Musculoskeletal Biology, Faculty of Health and Life Sciences, Institute of Ageing and Chronic Disease, University of Liverpool, Liverpool, UK
| | - Janos Fodor
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Peter Szentesi
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Tibor Hajdú
- Department of Anatomy, Histology and Embryology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Aniko Keller-Pinter
- Department of Biochemistry, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Erin Henslee
- Department of Mechanical Engineering Sciences, Centre for Biomedical Engineering, University of Surrey, Guildford, UK
| | - Fatima H Labeed
- Department of Mechanical Engineering Sciences, Centre for Biomedical Engineering, University of Surrey, Guildford, UK
| | - Michael P Hughes
- Department of Mechanical Engineering Sciences, Centre for Biomedical Engineering, University of Surrey, Guildford, UK
| | - Ali Mobasheri
- Department of Regenerative Medicine, State Research Institute Centre for Innovative Medicine, Vilnius, Lithuania.,Research Unit of Medical Imaging, Physics and Technology, Faculty of Medicine, University of Oulu, Oulu, Finland.,Departments of Orthopedics, Rheumatology and Clinical Immunology, University Medical Center Utrecht, Utrecht, The Netherlands.,Department of Joint Surgery, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
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Maleckar MM, Martín-Vasallo P, Giles WR, Mobasheri A. Physiological Effects of the Electrogenic Current Generated by the Na +/K + Pump in Mammalian Articular Chondrocytes. Bioelectricity 2020; 2:258-268. [PMID: 34471850 PMCID: PMC8370340 DOI: 10.1089/bioe.2020.0036] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Background: Although the chondrocyte is a nonexcitable cell, there is strong interest in gaining detailed knowledge of its ion pumps, channels, exchangers, and transporters. In combination, these transport mechanisms set the resting potential, regulate cell volume, and strongly modulate responses of the chondrocyte to endocrine agents and physicochemical alterations in the surrounding extracellular microenvironment. Materials and Methods: Mathematical modeling was used to assess the functional roles of energy-requiring active transport, the Na+/K+ pump, in chondrocytes. Results: Our findings illustrate plausible physiological roles for the Na+/K+ pump in regulating the resting membrane potential and suggest ways in which specific molecular components of pump can respond to the unique electrochemical environment of the chondrocyte. Conclusion: This analysis provides a basis for linking chondrocyte electrophysiology to metabolism and yields insights into novel ways of manipulating or regulating responsiveness to external stimuli both under baseline conditions and in chronic diseases such as osteoarthritis.
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Affiliation(s)
| | - Pablo Martín-Vasallo
- UD of Biochemistry and Molecular Biology, Universidad de La Laguna, San Cristóbal de La Laguna, Spain.,Instituto de Tecnologías Biomédicas de Canarias, Universidad de La Laguna, San Cristóbal de La Laguna, Spain
| | - Wayne R Giles
- Department of Physiology and Pharmacology, University of Calgary, Calgary, Canada
| | - Ali Mobasheri
- Research Unit of Medical Imaging, Physics and Technology, Faculty of Medicine, University of Oulu, Oulu, Finland.,Department of Regenerative Medicine, State Research Institute Centre for Innovative Medicine, Vilnius, Lithuania.,Department of Orthopedics, Rheumatology and Clinical Immunology, University Medical Center Utrecht, Utrecht, The Netherlands
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K + and Ca 2+ Channels Regulate Ca 2+ Signaling in Chondrocytes: An Illustrated Review. Cells 2020; 9:cells9071577. [PMID: 32610485 PMCID: PMC7408816 DOI: 10.3390/cells9071577] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2020] [Revised: 06/23/2020] [Accepted: 06/25/2020] [Indexed: 12/16/2022] Open
Abstract
An improved understanding of fundamental physiological principles and progressive pathophysiological processes in human articular joints (e.g., shoulders, knees, elbows) requires detailed investigations of two principal cell types: synovial fibroblasts and chondrocytes. Our studies, done in the past 8–10 years, have used electrophysiological, Ca2+ imaging, single molecule monitoring, immunocytochemical, and molecular methods to investigate regulation of the resting membrane potential (ER) and intracellular Ca2+ levels in human chondrocytes maintained in 2-D culture. Insights from these published papers are as follows: (1) Chondrocyte preparations express a number of different ion channels that can regulate their ER. (2) Understanding the basis for ER requires knowledge of (a) the presence or absence of ligand (ATP/histamine) stimulation and (b) the extraordinary ionic composition and ionic strength of synovial fluid. (3) In our chondrocyte preparations, at least two types of Ca2+-activated K+ channels are expressed and can significantly hyperpolarize ER. (4) Accounting for changes in ER can provide insights into the functional roles of the ligand-dependent Ca2+ influx through store-operated Ca2+ channels. Some of the findings are illustrated in this review. Our summary diagram suggests that, in chondrocytes, the K+ and Ca2+ channels are linked in a positive feedback loop that can augment Ca2+ influx and therefore regulate lubricant and cytokine secretion and gene transcription.
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