Benzamil sensitive ion channels contribute to volume regulation in canine chondrocytes

Temperature modulates PVN pre-sympathetic neurones via transient receptor potential ion channels

The paraventricular nucleus (PVN) of the hypothalamus plays a vital role in maintaining homeostasis and modulates cardiovascular function via autonomic pre-sympathetic neurones. We have previously shown that coupling between transient receptor potential cation channel subfamily V Member 4 (Trpv4) and small-conductance calcium-activated potassium channels (SK) in the PVN facilitate osmosensing, but since TRP channels are also thermosensitive, in this report we investigated the temperature sensitivity of these neurones. Methods: TRP channel mRNA was quantified from mouse PVN with RT-PCR and thermosensitivity of Trpv4-like PVN neuronal ion channels characterised with cell-attached patch-clamp electrophysiology. Following recovery of temperature-sensitive single-channel kinetic schema, we constructed a predictive stochastic mathematical model of these neurones and validated this with electrophysiological recordings of action current frequency. Results: 7 thermosensitive TRP channel genes were found in PVN punches. Trpv4 was the most abundant of these and was identified at the single channel level on PVN neurones. We investigated the thermosensitivity of these Trpv4-like channels; open probability (Po) markedly decreased when temperature was decreased, mediated by a decrease in mean open dwell times. Our neuronal model predicted that PVN spontaneous action current frequency (ACf) would increase as temperature is decreased and in our electrophysiological experiments, we found that ACf from PVN neurones was significantly higher at lower temperatures. The broad-spectrum channel blocker gadolinium (100 µM), was used to block the warm-activated, Ca2+-permeable Trpv4 channels. In the presence of gadolinium (100 µM), the temperature effect was largely retained. Using econazole (10 µM), a blocker of Trpm2, we found there were significant increases in overall ACf and the temperature effect was inhibited. Conclusion: Trpv4, the abundantly transcribed thermosensitive TRP channel gene in the PVN appears to contribute to intrinsic thermosensitive properties of PVN neurones. At physiological temperatures (37°C), we observed relatively low ACf primarily due to the activity of Trpm2 channels, whereas at room temperature, where most of the previous characterisation of PVN neuronal activity has been performed, ACf is much higher, and appears to be predominately due to reduced Trpv4 activity. This work gives insight into the fundamental mechanisms by which the body decodes temperature signals and maintains homeostasis.

Regulation of pain neurotransmitters and chondrocytes metabolism mediated by voltage-gated ion channels: A narrative review

Osteoarthritis (OA) is one of the leading causes of chronic pain and dysfunction. It is essential to comprehend the nature of pain and cartilage degeneration and its influencing factors on OA treatment. Voltage-gated ion channels (VGICs) are essential in chondrocytes and extracellular matrix (ECM) metabolism and regulate the pain neurotransmitters between the cartilage and the central nervous system. This narrative review focused primarily on the effects of VGICs regulating pain neurotransmitters and chondrocytes metabolism, and most studies have focused on voltage-sensitive calcium channels (VSCCs), voltage-gated sodium channels (VGSCs), acid-sensing ion channels (ASICs), voltage-gated potassium channels (VGKCs), voltage-gated chloride channels (VGCCs). Various ion channels coordinate to maintain the intracellular environment's homeostasis and jointly regulate metabolic and pain under normal circumstances. In the OA model, the ion channel transport of chondrocytes is abnormal, and calcium influx is increased, which leads to increased neuronal excitability. The changes in ion channels are strongly associated with the OA disease process and individual OA risk factors. Future studies should explore how VGICs affect the metabolism of chondrocytes and their surrounding tissues, which will help clinicians and pharmacists to develop more effective targeted drugs to alleviate the progression of OA disease.

DeepGANnel: Synthesis of fully annotated single molecule patch-clamp data using generative adversarial networks

Development of automated analysis tools for “single ion channel” recording is hampered by the lack of available training data. For machine learning based tools, very large training sets are necessary with sample-by-sample point labelled data (e.g., 1 sample point every 100microsecond). In an experimental context, such data are labelled with human supervision, and whilst this is feasible for simple experimental analysis, it is infeasible to generate the enormous datasets that would be necessary for a big data approach using hand crafting. In this work we aimed to develop methods to generate simulated ion channel data that is free from assumptions and prior knowledge of noise and underlying hidden Markov models. We successfully leverage generative adversarial networks (GANs) to build an end-to-end pipeline for generating an unlimited amount of labelled training data from a small, annotated ion channel “seed” record, and this needs no prior knowledge of theoretical dynamical ion channel properties. Our method utilises 2D CNNs to maintain the synchronised temporal relationship between the raw and idealised record. We demonstrate the applicability of the method with 5 different data sources and show authenticity with t-SNE and UMAP projection comparisons between real and synthetic data. The model would be easily extendable to other time series data requiring parallel labelling, such as labelled ECG signals or raw nanopore sequencing data.

The Homeostasis of Cartilage Matrix Remodeling and the Regulation of Volume-Sensitive Ion Channel

Degenerative joint diseases of the hips and knees are common and are accompanied by severe pain and movement disorders. At the microscopic level, the main characteristics of osteoarthritis are the continuous destruction and degeneration of cartilage, increased cartilage extracellular matrix catabolism, decreased anabolism, increased synovial fluid, and decreased osmotic pressure. Cell volume stability is mainly regulated by ion channels, many of which are expressed in chondrocytes. These ion channels are closely related to pain regulation, volume regulation, the inflammatory response, cell proliferation, apoptosis, and cell differentiation. In this review, we focus on the important role of volume control-related ion channels in cartilage matrix remodeling and summarize current views. In addition, the potential mechanism of the volume-sensitive anion channel LRRC8A in the early occurrence of osteoarthritis is discussed.

Mechanosensory and mechanotransductive processes mediated by ion channels in articular chondrocytes: Potential therapeutic targets for osteoarthritis

Articular cartilage consists of an extracellular matrix including many proteins as well as embedded chondrocytes. Articular cartilage formation and function are influenced by mechanical forces. Hind limb unloading or simulated microgravity causes articular cartilage loss, suggesting the importance of the healthy mechanical environment in articular cartilage homeostasis and implying a significant role of appropriate mechanical stimulation in articular cartilage degeneration. Mechanosensitive ion channels participate in regulating the metabolism of articular chondrocytes, including matrix protein production and extracellular matrix synthesis. Mechanical stimuli, including fluid shear stress, stretch, compression and cell swelling and decreased mechanical conditions (such as simulated microgravity) can alter the membrane potential and regulate the metabolism of articular chondrocytes via transmembrane ion channel-induced ionic fluxes. This process includes Ca2+ influx and the resulting mobilization of Ca2+ that is due to massive released Ca2+ from stores, intracellular cation efflux and extracellular cation influx. This review brings together published information on mechanosensitive ion channels, such as stretch-activated channels (SACs), voltage-gated Ca2+ channels (VGCCs), large conductance Ca2+-activated K+ channels (BKCa channels), Ca2+-activated K+ channels (SKCa channels), voltage-activated H+ channels (VAHCs), acid sensing ion channels (ASICs), transient receptor potential (TRP) family channels, and piezo1/2 channels. Data based on epithelial sodium channels (ENaCs), purinergic receptors and N-methyl-d-aspartate (NMDA) receptors are also included. These channels mediate mechanoelectrical physiological processes essential for converting physical force signals into biological signals. The primary channel-mediated effects and signaling pathways regulated by these mechanosensitive ion channels can influence the progression of osteoarthritis during the mechanosensory and mechanoadaptive process of articular chondrocytes.

Ion Selectivity in the ENaC/DEG Family: A Systematic Review with Supporting Analysis

The Epithelial Sodium Channel/Degenerin (ENaC/DEG) family is a superfamily of sodium-selective channels that play diverse and important physiological roles in a wide variety of animal species. Despite their differences, they share a high homology in the pore region in which the ion discrimination takes place. Although ion selectivity has been studied for decades, the mechanisms underlying this selectivity for trimeric channels, and particularly for the ENaC/DEG family, are still poorly understood. This systematic review follows PRISMA guidelines and aims to determine the main components that govern ion selectivity in the ENaC/DEG family. In total, 27 papers from three online databases were included according to specific exclusion and inclusion criteria. It was found that the G/SxS selectivity filter (glycine/serine, non-conserved residue, serine) and other well conserved residues play a crucial role in ion selectivity. Depending on the ion type, residues with different properties are involved in ion permeability. For lithium against sodium, aromatic residues upstream of the selectivity filter seem to be important, whereas for sodium against potassium, negatively charged residues downstream of the selectivity filter seem to be important. This review provides new perspectives for further studies to unravel the mechanisms of ion selectivity.

Dielectrophoresis as a Tool to Reveal the Potential Role of Ion Channels and Early Electrophysiological Changes in Osteoarthritis

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.

Transcriptome-based screening of ion channels and transporters in a migratory chondroprogenitor cell line isolated from late-stage osteoarthritic cartilage

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.

The potential role of mechanically sensitive ion channels in the physiology, injury, and repair of articular cartilage

Biomechanical factors play an extremely important role in regulating the function of articular chondrocytes. Understanding the mechanical factors that drive chondrocyte biological responses is at the heart of our interpretation of cascade events leading to changes in articular cartilage osteoarthritis. The mechanism by which mechanical load is transduced into intracellular signals that can regulate chondrocyte gene expression remains largely unknown. The mechanically sensitive ion channel (MSC) may be one of its specific mechanisms. This review focuses on four ion channels involved in the mechanotransduction of chondrocytes, exploring their properties and the main factors that activate the associated pathways. The upstream and downstream potential relationships between the protein pathways were also explored. The specific biophysical mechanism of the chondrocyte mechanical microenvironment is becoming the focus of research. Elucidating the mechanotransduction mechanism of MSC is essential for the research of biophysical pathogenesis and targeted drugs in cartilage injury-related diseases.

Articular Chondrocyte Phenotype Regulation through the Cytoskeleton and the Signaling Processes That Originate from or Converge on the Cytoskeleton: Towards a Novel Understanding of the Intersection between Actin Dynamics and Chondrogenic Function

Numerous studies have assembled a complex picture, in which extracellular stimuli and intracellular signaling pathways modulate the chondrocyte phenotype. Because many diseases are mechanobiology-related, this review asked to what extent phenotype regulators control chondrocyte function through the cytoskeleton and cytoskeleton-regulating signaling processes. Such information would generate leverage for advanced articular cartilage repair. Serial passaging, pro-inflammatory cytokine signaling (TNF-α, IL-1α, IL-1β, IL-6, and IL-8), growth factors (TGF-α), and osteoarthritis not only induce dedifferentiation but also converge on RhoA/ROCK/Rac1/mDia1/mDia2/Cdc42 to promote actin polymerization/crosslinking for stress fiber (SF) formation. SF formation takes center stage in phenotype control, as both SF formation and SOX9 phosphorylation for COL2 expression are ROCK activity-dependent. Explaining how it is molecularly possible that dedifferentiation induces low COL2 expression but high SF formation, this review theorized that, in chondrocyte SOX9, phosphorylation by ROCK might effectively be sidelined in favor of other SF-promoting ROCK substrates, based on a differential ROCK affinity. In turn, actin depolymerization for redifferentiation would “free-up” ROCK to increase COL2 expression. Moreover, the actin cytoskeleton regulates COL1 expression, modulates COL2/aggrecan fragment generation, and mediates a fibrogenic/catabolic expression profile, highlighting that actin dynamics-regulating processes decisively control the chondrocyte phenotype. This suggests modulating the balance between actin polymerization/depolymerization for therapeutically controlling the chondrocyte phenotype.

Physiological Effects of the Electrogenic Current Generated by the Na+/K+ Pump in Mammalian Articular Chondrocytes

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.

Pro-inflammatory Cytokines Drive Deregulation of Potassium Channel Expression in Primary Synovial Fibroblasts

The synovium secretes synovial fluid, but is also richly innervated with nociceptors and acts as a gateway between avascular joint tissues and the circulatory system. Resident fibroblast-like synoviocytes' (FLS) calcium-activated potassium channels (K _Ca) change in activity in arthritis models and this correlates with FLS activation.

Objective

To investigate this activation in an in vitro model of inflammatory arthritis; 72 h treatment with cytokines TNFα and IL1β.

Methods

FLS cells were isolated from rat synovial membranes. We analyzed global changes in FLS mRNA by RNA-sequencing, then focused on FLS ion channel genes and the corresponding FLS electrophysiological phenotype and finally modeling data with ingenuity pathway analysis (IPA) and MATLAB.

Results

IPA showed significant activation of inflammatory, osteoarthritic and calcium signaling canonical pathways by cytokines, and we identified ∼200 channel gene transcripts. The large K _Ca (BK) channel consists of the pore forming Kcnma1 together with β-subunits. Following cytokine treatment, a significant increase in Kcnma1 RNA abundance was detected by qPCR and changes in several ion channels were detected by RNA-sequencing, including a loss of BK channel β-subunit expression Kcnmb1/2 and an increase in Kcnmb3. In electrophysiological experiments, there was a decrease in over-all current density at 20 mV without change in chord conductance at this potential.

Conclusion

TNFα and IL1β treatment of FLS in vitro recapitulated several common features of inflammatory arthritis at the transcriptomic level, including increase in Kcnma1 and Kcnmb3 gene expression.

Physiological and Pathological Functions of Cl- Channels in Chondrocytes

Articular chondrocytes are embedded in the cartilage of diarthrodial joints and responsible for the synthesis and secretion of extracellular matrix. The extracellular matrix mainly contains collagens and proteoglycans, and covers the articular cartilage to protect from mechanical and biochemical stresses. In mammalian chondrocytes, various types of ion channels have been identified: e.g., voltage-dependent K⁺ channels, Ca²⁺-activated K⁺ channels, ATP-sensitive K⁺ channels, two-pore domain K⁺ channels, voltage-dependent Ca²⁺ channels, store-operated Ca²⁺ channels, epithelial Na⁺ channels, acid-sensing ion channels, transient receptor potential channels, and mechanosensitive channels. These channels play important roles for the regulation of resting membrane potential, Ca²⁺ signaling, pH sensing, mechanotransduction, and cell proliferation in articular chondrocytes. In addition to these cation channels, Cl^- channels are known to be expressed in mammalian chondrocytes: e.g., voltage-dependent Cl^- channels, cystic fibrosis transmembrane conductance regulator channels, swelling-activated Cl^- channels, and Ca²⁺-activated Cl^- channels. Although these chondrocyte Cl^- channels are thought to contribute to the regulation of resting membrane potential, Ca²⁺ signaling, cell volume, cell survival, and endochondral bone formation, the physiological functions have not been fully clarified. Osteoarthritis (OA) is caused by the degradation of articular cartilage, resulting in inflammation and pain in the joints. Therefore the pathophysiological roles of Cl^- channels in OA chondrocytes are of considerable interest. Elucidating the physiological and pathological functions of chondrocyte Cl^- channels will provide us a more comprehensive understanding of chondrocyte functions and may suggest novel molecular targets of drug development for OA.

Activation of a chondrocyte volume-sensitive Cl(-) conductance prior to macroscopic cartilage lesion formation in the rabbit knee anterior cruciate ligament transection osteoarthritis model

OBJECTIVE

The anterior cruciate ligament transection (ACLT) rabbit osteoarthritis (OA) model confers permanent knee instability and induces joint degeneration. The degeneration process is complex, but includes chondrocyte apoptosis and OA-like loss of cartilage integrity. Previously, we reported that activation of a volume-sensitive Cl(-) current (ICl,vol) can mediate cell shrinkage and apoptosis in rabbit articular chondrocytes. Our objective was therefore to investigate whether ICl,vol was activated in the early stages of the rabbit ACLT OA model.

DESIGN

Adult Rabbits underwent unilateral ACLT and contralateral arthrotomy (sham) surgery. Rabbits were euthanized at 2 or 4 weeks. Samples were analyzed histologically and with assays of cell volume, apoptosis and electrophysiological characterization of ICl,vol.

RESULTS

At 2 and 4 weeks post ACLT cartilage appeared histologically normal, nevertheless cell swelling and caspase 3/7 activity were both significantly increased compared to sham controls. In cell-volume experiments, exposure of chondrocytes to hypotonic solution led to a greater increase in cell size in ACLT compared to controls. Caspase-3/7 activity, an indicator of apoptosis, was elevated in both ACLT 2wk and 4wk. Whole-cell currents were recorded with patch clamp of chondrocytes in iso-osmotic and hypo-osmotic external solutions under conditions where Na(+), K(+) and Ca(2+) currents were minimized. ACLT treatment resulted in a large increase in hypotonic-activated chloride conductance.

CONCLUSION

Changes in chondrocyte ion channels take place prior to the onset of apparent cartilage loss in the ACLT rabbit model of OA. Further studies are needed to investigate if pharmacological inhibition of ICl,vol decreases progression of OA in animal models.

Membrane channel gene expression in human costal and articular chondrocytes

Chondrocytes are the uniquely resident cells found in all types of cartilage and key to their function is the ability to respond to mechanical loads with changes of metabolic activity. This mechanotransduction property is, in part, mediated through the activity of a range of expressed transmembrane channels; ion channels, gap junction proteins, and porins. Appropriate expression of ion channels has been shown essential for production of extracellular matrix and differential expression of transmembrane channels is correlated to musculoskeletal diseases such as osteoarthritis and Albers-Schönberg. In this study we analyzed the consistency of gene expression between channelomes of chondrocytes from human articular and costal (teenage and fetal origin) cartilages. Notably, we found 14 ion channel genes commonly expressed between articular and both types of costal cartilage chondrocytes. There were several other ion channel genes expressed only in articular (6 genes) or costal chondrocytes (5 genes). Significant differences in expression of BEST1 and KCNJ2 (Kir2.1) were observed between fetal and teenage costal cartilage. Interestingly, the large Ca²⁺ activated potassium channel (BKα, or KCNMA1) was very highly expressed in all chondrocytes examined. Expression of the gap junction genes for Panx1, GJA1 (Cx43) and GJC1 (Cx45) was also observed in chondrocytes from all cartilage samples. Together, this data highlights similarities between chondrocyte membrane channel gene expressions in cells derived from different anatomical sites, and may imply that common electrophysiological signaling pathways underlie cellular control. The high expression of a range of mechanically and metabolically sensitive membrane channels suggest that chondrocyte mechanotransduction may be more complex than previously thought.

Changes in Membrane Receptors and Ion Channels as Potential Biomarkers for Osteoarthritis

Osteoarthritis (OA), a degenerative joint condition, is currently difficult to detect early enough for any of the current treatment options to be completely successful. Early diagnosis of this disease could increase the numbers of patients who are able to slow its progression. There are now several diseases where membrane protein biomarkers are used for early diagnosis. The numbers of proteins in the membrane is vast and so it is a rich source of potential biomarkers for OA but we need more knowledge of these before they can be considered practical biomarkers. How are they best measured and are they selective to OA or even certain types of OA? The first step in this process is to identify membrane proteins that change in OA. Here, we summarize several ion channels and receptors that change in OA models and/or OA patients, and may thus be considered candidates as novel membrane biomarkers of OA.

TRPV4 and K(Ca) ion channels functionally couple as osmosensors in the paraventricular nucleus

BACKGROUND AND PURPOSE

Transient receptor potential vanilloid type 4 (TRPV4) and calcium-activated potassium channels (KCa ) mediate osmosensing in many tissues. Both TRPV4 and KCa channels are found in the paraventricular nucleus (PVN) of the hypothalamus, an area critical for sympathetic control of cardiovascular and renal function. Here, we have investigated whether TRPV4 channels functionally couple to KCa channels to mediate osmosensing in PVN parvocellular neurones and have characterized, pharmacologically, the subtype of KCa channel involved.

EXPERIMENTAL APPROACH

We investigated osmosensing roles for TRPV4 and KCa channels in parvocellular PVN neurones using cell-attached and whole-cell electrophysiology in mouse brain slices and rat isolated PVN neurons. Intracellular Ca(2+) was recorded using Fura-2AM. The system was modelled in the NEURON simulation environment.

KEY RESULTS

Hypotonic saline reduced action current frequency in hypothalamic slices; a response mimicked by TRPV4 channel agonists 4αPDD (1 μM) and GSK1016790A (100 nM), and blocked by inhibitors of either TRPV4 channels (RN1734 (5 μM) and HC067047 (300 nM) or the low-conductance calcium-activated potassium (SK) channel (UCL-1684 30 nM); iberiotoxin and TRAM-34 had no effect. Our model was compatible with coupling between TRPV4 and KCa channels, predicting the presence of positive and negative feedback loops. These predictions were verified using isolated PVN neurons. Both hypotonic challenge and 4αPDD increased intracellular Ca(2+) and UCL-1684 reduced the action of hypotonic challenge.

CONCLUSIONS AND IMPLICATIONS

There was functional coupling between TRPV4 and SK channels in parvocellular neurones. This mechanism contributes to osmosensing in the PVN and may provide a novel pharmacological target for the cardiovascular or renal systems.

Chondrocyte channel transcriptomics: do microarray data fit with expression and functional data?

To date, a range of ion channels have been identified in chondrocytes using a number of different techniques, predominantly electrophysiological and/or biomolecular; each of these has its advantages and disadvantages. Here we aim to compare and contrast the data available from biophysical and microarray experiments. This letter analyses recent transcriptomics datasets from chondrocytes, accessible from the European Bioinformatics Institute (EBI). We discuss whether such bioinformatic analysis of microarray datasets can potentially accelerate identification and discovery of ion channels in chondrocytes. The ion channels which appear most frequently across these microarray datasets are discussed, along with their possible functions. We discuss whether functional or protein data exist which support the microarray data. A microarray experiment comparing gene expression in osteoarthritis and healthy cartilage is also discussed and we verify the differential expression of 2 of these genes, namely the genes encoding large calcium-activated potassium (BK) and aquaporin channels.

Potassium channels in articular chondrocytes

Chondrocytes are the resident cells of cartilage, which synthesize and maintain the extracellular matrix. The range of known potassium channels expressed by these unique cells is continually increasing. Since chondrocytes are non-excitable, and do not need to be repolarized following action potentials, the function of potassium channels in these cells has, until recently, remained completely unknown. However, recent advances in both traditional physiology and “omic” technologies have enhanced our knowledge and understanding of the chondrocyte channelome. A large number of potassium channels have been identified and a number of putative, but credible, functions have been proposed. Members of each of the potassium channel sub-families (calcium activated, inward rectifier, voltage-gated and tandem pore) have all been identified. Mechanotransduction, cell volume regulation, apoptosis and chondrogenesis all appear to involve potassium channels. Since evidence suggests that potassium channel gene transcription is altered in osteoarthritis, future studies are needed that investigate potassium channels as potential cellular biomarkers and therapeutic targets for treatment of degenerative joint conditions.