TRP Family Of Ion Channels Research Articles

TRPC6 deficiency impairs middle cerebral artery myogenic response and brain spatial memory

Transient receptor potential channel 6 (TRPC6) is a nonselective cation channel belonging to the TRP ion channel family and expressed in vascular smooth muscle cells. TRPC6 regulates calcium influx in response to vascular wall mechanical stretch. A previous study reported that TRPC6 is critical for the myogenic response of the middle cerebral artery (MCA). Impaired MCA myogenic response is implicated in cerebral blood flow dysfunction and may promote cognitive deficits. In this study, we investigated whether TRPC6 contributes to the MCA myogenic response at pressure range (from 40 to 180 mmHg) in 12-week-old male wild-type (WT) and whole-body TRPC6 knock-out (TRPC6 KO) mice (n=5-8). Cognitive function (spatial learning and reference memory) was examined at 22 weeks of age using the Morris water maze test. Myogenic response in MCA was similar in WT and TRPC6 KO mice when perfusion pressure was increased from 40 to 80 mmHg. At higher pressures (>120 mmHg), however, TRPC6 KO mice displayed significantly reduced myogenic response compared to WT mice (3 % less of myogenic tone in TRPC6 KO compared to WT) which was further exacerbated when perfusion pressure was increased to 180 mmHg (9 % less of myogenic tone in TRPC6 KO compared to WT). There were no significant differences in wall thickness, wall-to-lumen ratio, vascular distensibility, incremental distensibility, or elastic modulus curves in MCA between WT and TRPC6 KO mice. Compared to WT mice, TRPC6 KO mice displayed similar spatial learning curves after 4 days of training but showed significantly impaired reference memory (14±1 % vs 29±4 % in the target quadrant) and reduced frequency (1.0±0.3 vs 2.1±0.4 in the target area crossing) compared to WT. These findings suggest that TRPC6 deficiency impairs myogenic response at higher perfusion pressures and spatial memory, even at a young age. (AG050049 (F.F), AG057842 (F.F), AG079336 (F.F), NIDDK R00DK113280, R01DK121411, NIGMS P20GM104357 and NIGMS U54GM115428) This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The Mechanisms of Plasticity of Nociceptive Ion Channels in Painful Diabetic Neuropathy.

Treating pain in patients suffering from small fiber neuropathies still represents a therapeutic challenge for health care providers and drug developers worldwide. Unfortunately, none of the currently available treatments can completely reverse symptoms of either gain or loss of peripheral nerve sensation. Therefore, there is a clear need for novel mechanism-based therapies for peripheral diabetic neuropathy (PDN) that would improve treatment of this serious condition. In this review, we summarize the current knowledge on the mechanisms and causes of peripheral sensory neurons damage in diabetes. In particular, we focused on the subsets of voltage-gated sodium channels, TRP family of ion channels and a CaV3.2 isoform of T-type voltage-gated calcium channels. However, even though their potential is well-validated in multiple rodent models of painful PDN, clinical trials with specific pharmacological blockers of these channels have failed to exhibit therapeutic efficacy. We argue that understanding the development of diabetes and causal relationship between hyperglycemia, glycosylation, and other post-translational modifications may lead to the development of novel therapeutics that would efficiently alleviate painful PDN by targeting disease-specific mechanisms rather than individual nociceptive ion channels.

Covering the Cover

Covering the Cover

Investigating the Structure‐Function Relationship Between TRPV1 Channels and Pain

Transient receptor potential, or TRP, ion channels are a superfamily of non-selective cation transmembrane proteins expressed in many tissues. These channels play a key role in the sensory signaling of taste, thermosensation, mechanosensation, and nociception. Transient receptor potential vanilloid 1, or TRPV1, a member of the TRP family of ion channels, specifically responds to both heat and spice. The activation of this channel occurs when a ligand, such as capsaicin, binds to the ligand-binding site, replacing phosphatidylinositol lipids. Capsaicin is a chemical compound commonly found in chili peppers that transmits sensation of taste and pain when it binds to TRPV1. Neuropathic pain, inflammation, and reduced ability to detect stimuli are all symptoms associated with dysfunctional TRPV ion channels. The Summit Country Day School MSOE Center for Biomolecular Modeling MAPS Team used 3D modeling and printing technology to examine the structure-function relationship of the interaction between the TRPV1 ion channel and capsaicin. TRPV ion channels are homotetramers, and individual polypeptide chains contain a transmembrane domain composed of the pore region and vanilloid binding pocket. Capsaicin molecules have been shown to bind to the vanilloid binding pocket located above the S4-S5 linker of one monomer of the TRPV1 tetramer. Two main restriction points in the ion permeation channel were identified. A vanilloid agonist displaces phosphatidylinositide, facilitating the formation of a salt bridge between Arg557 and Glu570, which pulls the S4-S5 linker away from the central axis, opening the lower gate of the pore. The binding of capsaicin to the pocket leaves the selective permeability filter closed but the lower ion gate partially open. This channel is considered as a possible target for the creation of therapeutic treatments for chronic pain. TRPV1 antagonists, such as capsaicin, may play a key role in blocking chronic pain. Capsaicin is already used as a component in topical pain patches and natural and synthetic molecules related to capsaicin have been tested for their ability to decrease response to pain. In the recent movement to decrease the prescription of brain-based pain-blocking medication in response to the opioid epidemic, TRPV1 channels may play a significant role in the development of new therapeutic options in the treatment of pain.

Mammalian TRP Ion Channels are Insensitive to Membrane Stretch

TRP channels of the transient receptor potential ion channel superfamily are involved in a wide variety of mechanosensory processes, including touch sensation, pain, blood pressure regulation, bone loading, and detection of cerebrospinal fluid flow. However, it is unclear in many instances whether TRP channels are the primary transducers of mechanical force in these processes. In this study, we tested stretch activation of eleven TRP channels from six subfamilies. We found that these TRP channels were insensitive to short membrane stretch in cellular systems. Furthermore, we purified TRPC6 and demonstrated its insensitivity to stretch in liposomes, an artificial bilayer system free from cellular components. Additionally, we demonstrated that when expressed in C. elegans neurons, mouse TRPC6 restores the mechanoresponse of a touch insensitive mutant but requires diacylglycerol for activation. These results strongly suggest that the mammalian members of the TRP ion channel family are insensitive to tension induced by cell membrane stretching and thus they are more likely activated by cytoplasmic tethers or downstream components and act as amplifiers of cellular mechanosensory signaling cascades.

Mammalian TRP ion channels are insensitive to membrane stretch.

ABSTRACTTRP channels of the transient receptor potential ion channel superfamily are involved in a wide variety of mechanosensory processes, including touch sensation, pain, blood pressure regulation, bone loading and detection of cerebrospinal fluid flow. However, in many instances it is unclear whether TRP channels are the primary transducers of mechanical force in these processes. In this study, we tested stretch activation of eleven TRP channels from six mammalian subfamilies. We found that these TRP channels were insensitive to short membrane stretches in cellular systems. Furthermore, we purified TRPC6 and demonstrated its insensitivity to stretch in liposomes, an artificial bilayer system free from cellular components. Additionally, we demonstrated that, when expressed in C. elegans neurons, mouse TRPC6 restores the mechanoresponse of a touch insensitive mutant but requires diacylglycerol for activation. These results strongly suggest that the mammalian members of the TRP ion channel family are insensitive to tension induced by cell membrane stretching and, thus, are more likely to be activated by cytoplasmic tethers or downstream components and to act as amplifiers of cellular mechanosensory signaling cascades.

Potentiation of TRPM5 with Stevioside in the Beta Cells Stimulates Insulin Secretion

The calcium-activated monovalent cation channel TRPM5 is expressed in human and murine beta cells. Members of the TRP ion channel family can be activated by a plethora of different stimuli as temperature, voltage, and ligands, including natural compounds. Studies have shown that TrpM5-knockout mice have increased blood glucose levels and an impaired insulin secretion. Mutations in TRPM5 are more prevalent in patients with diabetes or metabolic syndrome. Stevioside is a sweet tasting organic molecule isolated from the leaves of the scrub plant Stevia rebaudiana, it is widely used in consumer foods and beverages. Despite its wide use, the molecular interactions of stevioside in the body remained elusive. Here we show that stevioside potentiates TRPM5 channel activity. This leads to increased calcium dynamics in both human and mouse islets, which relates to increased insulin secretion. We show that the steviol core of stevioside is responsible for the TRPM5-potentiating effect. When mice on a high fat diet are given stevioside, we observe an attenuation of the development of hyperglycemia in a TRPM5-dependent manner. With this work, we elucidate the molecular mechanism of action of stevioside. Furthermore, we provide a deeper insight in the regulation of insulin secretion from the beta-cells and identify TRPM5 as an important part of a healthy secretion pathway. TRPM5 constitutes a novel possible drug target in the battle against type 2 diabetes. Disclosure K. Philippaert: None. R. Vennekens: None. P.E. Light: None.

The Mechanism of Regulation of TRPV6 Channels by PI(4,5)P2

Transient Receptor Potential Vanilloid 6 (TRPV6) is a Ca2+ selective ion channel playing important roles in intestinal Ca2+ absorption, male fertility and cancer development. TRPV6 is a member of the highly diverse TRP ion channel family. The only known common functional feature among TRP channels is their dependence on, and modulation by phosphoinositides, mostly phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2]. Most TRP channels require factors other than PI(4,5)P2 to open, which are often in complex interaction with PI(4,5)P2 regulation, which hinders understanding of the molecular mechanism of how PI(4,5)P2 opens these channels. TRPV6 is constitutively active, thus devoid of these complexities, and therefore is an ideal model to gain molecular insight into regulation by PI(4,5)P2. We computationally docked PI(4,5)P2 to both TRPV6, and the heat and capsaicin sensitive TRPV1. We find that PI(4,5)P2 binds to TRPV1 mainly in the proximal C-terminus and in the S4-S5 linker, consistent with earlier predictions, and experimental data. In TRPV6, however, the closest interacting residues were in the proximal N-terminus, close to the first transmembrane region and, similar to TRPV1, in the S4-S5 linker. Introduction of a positive charge in the S4-S5 linker that is missing from TRPV6, but present in TRPV1, markedly increased the affinity of TRPV6 to PI(4,5)P2. Neutralizing a proximal N-terminal positively charged residue predicted to interact with PI(4,5)P2 markedly reduced current TRPV6 amplitudes, but neutralizing neighboring positively charged residues had no effect. Our data will provide mechanistic insight into PI(4,5)P2 regulation of TRPV6.

Ca(2+) binding protein S100A1 competes with calmodulin and PIP2 for binding site on the C-terminus of the TPRV1 receptor.

Transient receptor potential vanilloid 1 ion channel (TRPV1) belongs to the TRP family of ion channels. These channels play a role in many important biological processes such as thermosensation and pain transduction. The TRPV1 channel was reported to be also involved in nociception. Ca(2+) ions are described to participate in the regulation of TRP channels through the interaction with Ca(2+)-binding proteins, such as calmodulin or S100A1. Calmodulin is involved in the Ca(2+)-dependent regulation of TRPV1 via its binding to the TRPV1 C-terminal region. However, the role of the Ca(2+)-binding protein S100A1 in the process of TRP channel regulation remains elusive. Here we characterized a region on the TRPV1 C-terminus responsible for the interaction with S100A1 using biochemical and biophysical tools. We found that this region overlaps with previously identified calmodulin and PIP2 binding sites and that S100A1 competes with calmodulin and PIP2 for this binding site. We identified several positively charged residues within this region, which have crucial impact on S100A1 binding, and we show that the reported S100A1-TRPV1 interaction is calcium-dependent. Taken together, our data suggest a mechanism for the mutual regulation of PIP2 and the Ca(2+)-binding proteins S100A1 and calmodulin to TRPV1.

A high-resolution structure of the EF-hand domain of human polycystin-2.

Autosomal dominant polycystic kidney disease (ADPKD) affects over 1:1000 of the worldwide population and is caused by mutations in two genes, PKD1 and PKD2. PKD2 encodes a 968-amino acid membrane spanning protein, Polycystin-2 (PC-2), which is a member of the TRP ion channel family. The C-terminal cytoplasmic tail contains an EF-hand motif followed by a short coiled-coil domain. We have determined the structure of the EF-hand region of PC-2 using NMR spectroscopy. The use of different boundaries, compared with those used in previous studies, have enabled us to determine a high resolution structure and show that the EF hand motif forms a standard calcium-binding pocket. The affinity of this pocket for calcium has been measured and mutants that both decrease and increase its affinity for the metal ion have been created.

The role of endogenous molecules in modulating pain through transient receptor potential vanilloid 1 (TRPV1)

Pain is a physiological response to a noxious stimulus that decreases the quality of life of those sufferring from it. Research aimed at finding new therapeutic targets for the treatment of several maladies, including pain, has led to the discovery of numerous molecular regulators of ion channels in primary afferent nociceptive neurons. Among these receptors is TRPV1 (transient receptor potential vanilloid 1), a member of the TRP family of ion channels. TRPV1 is a calcium-permeable channel, which is activated or modulated by diverse exogenous noxious stimuli such as high temperatures, changes in pH, and irritant and pungent compounds, and by selected molecules released during tissue damage and inflammatory processes. During the last decade the number of endogenous regulators of TRPV1's activity has increased to include lipids that can negatively regulate TRPV1, as is the case for cholesterol and PIP2 (phosphatidylinositol 4,5-biphosphate) while, in contrast, other lipids produced in response to tissue injury and ischaemic processes are known to positively regulate TRPV1. Among the latter, lysophosphatidic acid activates TRPV1 while amines such as N-acyl-ethanolamines and N-acyl-dopamines can sensitize or directly activate TRPV1. It has also been found that nucleotides such as ATP act as mediators of chemically induced nociception and pain and gases, such as hydrogen sulphide and nitric oxide, lead to TRPV1 activation. Finally, the products of lipoxygenases and omega-3 fatty acids among other molecules, such as divalent cations, have also been shown to endogenously regulate TRPV1 activity. Here we provide a comprehensive review of endogenous small molecules that regulate the function of TRPV1. Acting through mechanisms that lead to sensitization and desensitization of TRPV1, these molecules regulate pathways involved in pain and nociception. Understanding how these compounds modify TRPV1 activity will allow us to comprehend how some pathologies are associated with its deregulation.

Sphingosine and the transient receptor potential channel kinase(s)

Transient receptor potential melastatin 7 (TRPM7) is a multifunctional ion channel playing crucial roles during development. TRPM7 is a member of the highly diverse TRP ion channel family. Most TRP channels are regulated by membrane phospholipids, especially phosphoinositides. In this issue of the British Journal of Pharmacology, Qin et al. describes the regulation of TRPM7 and its close homologue TRPM6 by a different kind of membrane lipid: sphingosine. The study finds that sphingosine is a potent and specific inhibitor of TRPM7 and TRPM6 channels. This commentary briefly summarizes the findings of the study, their potential significance and discusses open question and future directions.

The transient receptor potential channel TRPA1: from gene to pathophysiology

The Transient Receptor Potential Ankyrin 1 channel (TRPA1), is a member of the large TRP family of ion channels, and functions as a Ca(2+) permeable non-selective cation channel in many different cell processes, ranging from sensory to homeostatic tasks. TRPA1 is highly conserved across the animal kingdom. The only mammalian TRPA subfamily member, TRPA1, is widely expressed in neuronal (e.g. sensory dorsal root and trigeminal ganglia neurons)- and in non-neuronal cells (e.g. epithelial cells, hair cells). It exhibits 14-19 amino-(N-)terminal ankyrin repeats, an unusual structural feature. The TRPA1 channel is activated by noxious cold (<17°C) as well as by a plethora of chemical compounds that includes not only electrophilic compounds and oxidants that can modify, in an alkylative or oxidative fashion, nucleophilic cysteine residues in the channel's N-terminus, but also compounds that do not covalently bind to the channel proteins (e.g. menthol, nifedipin). Based on localization and functional properties, TRPA1 is considered a key player in acute and chronic (neuropathic) pain and inflammation. Moreover, its role in the (patho)physiology of nearly all organ systems is anticipated, and will be discussed along with the potential of TRPA1 as a drug target for the management of various pathological conditions.

A Gateway MultiSite Recombination Cloning Toolkit

The generation of DNA constructs is often a rate-limiting step in conducting biological experiments. Recombination cloning of single DNA fragments using the Gateway system provided an advance over traditional restriction enzyme cloning due to increases in efficiency and reliability. Here we introduce a series of entry clones and a destination vector for use in two, three, and four fragment Gateway MultiSite recombination cloning whose advantages include increased flexibility and versatility. In contrast to Gateway single-fragment cloning approaches where variations are typically incorporated into model system-specific destination vectors, our Gateway MultiSite cloning strategy incorporates variations in easily generated entry clones that are model system-independent. In particular, we present entry clones containing insertions of GAL4, QF, UAS, QUAS, eGFP, and mCherry, among others, and demonstrate their in vivo functionality in Drosophila by using them to generate expression clones including GAL4 and QF drivers for various trp ion channel family members, UAS and QUAS excitatory and inhibitory light-gated ion channels, and QUAS red and green fluorescent synaptic vesicle markers. We thus establish a starter toolkit of modular Gateway MultiSite entry clones potentially adaptable to any model system. An inventory of entry clones and destination vectors for Gateway MultiSite cloning has also been established (www.gatewaymultisite.org).

Transient Receptor Potential Melastatin Type 7 Channel Is Critical for the Survival of Bone Marrow Derived Mesenchymal Stem Cells

The transient receptor potential melastatin type 7 channel (TRPM7) is a member of the TRP family of ion channels that is essential for cell proliferation and viability. Mesenchymal stem cells (MSCs) from bone marrow are a potential source for tissue repair due to their ability to differentiate into specialized cells. However, the role of TRPM7 in stem cells is unknown. In this study, we characterized TRPM7 in mouse MSCs using molecular biology, immunocytochemistry, and patch clamp. We also investigated TRPM7 function using a lentiviral vector and specific shRNA to knockdown gene expression. By RT-PCR and immunocytochemistry, we identified TRPM7, but not TRPM6, a close family member with similar function. Electrophysiological recordings during depletion of intracellular Mg(2+) or Mg(2+)-ATP resulted in the development of currents typical for the channel. Furthermore, 2-aminoethoxydiphenyl borate (1 pM-100 microM) inhibited TRPM7 in a concentration-dependent manner. The molecular suppression of TRPM7 significantly decreased MSC proliferation and viability as determined by MTT assay. In addition, TRPM7 gene expression was up-regulated during osteogenesis. These findings demonstrate that TRPM7 is required for MSC survival and perhaps involved in the differentiation process.

Patch Clamped Giant Unilamellar Vesicles Containing Reconstituted Ion Channels

There is increasing interest in how the chemical and physical properties of lipid membranes affect the function of mammalian ion channels. As evidenced by recent work on KvAP and Kv1.2, as well as studies of the physical nature of patches themselves, these effects are both intriguing and difficult to study. For the TRP family of ion channels these questions are especially important as membrane lipids, such as phosphoinositide (4,5) bisphosphate (PIP2), play an active role in regulating their functional properties. Although much work has been done to address the mechanism by which lipids regulate TRP channels in intact cells and excised patches, the physical interactions that govern channel regulation are still unknown. We report here on our efforts to establish high resolution control over membrane chemical composition and physical properties. We find that giant unilammelar vesicles can be synthesized with desired lipid compositions and subsequently studied using patch-clamp techniques. Reconstitution of functional TRP channels into these synthetic lipid membranes would provide a well-controlled experimental paradigm for studying the function and mechanism of channel-lipid interactions.

The Second American Cough Conference

Two years after our inaugural meeting [1], the Second American Cough Conference was held in June 2009 on the banks of the Hudson River, in the shadow of the New York City skyline. Once again, a faculty of internationally renowned basic and clinical scientists provided state-ofthe-art summaries and updated developments in the recently energized field of cough. The audience filling the auditorium to capacity comprised a broad range of interested parties: researchers, academicians, clinicians, and members of the pharmaceutical industry. Reflecting the multidisciplinary challenge that pathological cough presents, conference speakers represented a broad range of backgrounds: basic and preclinical science, respiratory medicine, allergology, otorhinolaryngology, biomedical engineering, and pediatrics. As is the goal of the American Cough Conference, new and emerging themes, involving mechanisms, diagnosis, and management of cough, were presented and discussed. Notable among these is the concept that a preexisting, heightened cough reflex may underlie the development of chronic cough in susceptible individuals upon the superimposition of a second, exacerbating factor such as acute viral upper respiratory tract infection or gastroesophageal reflux, whereas in others with less sensitive baseline cough reflex sensitivity, identical triggers will not result in the onset of cough [2]. New developments in the pharmacology of cough were prominently featured, including an update on the TRP family of ion channels. Whereas the TRPV1 ion channel has received significant attention as a potential target for antitussive drugs [3], the TRPA1 channel is now identified as a particularly exciting area of investigation. Recently emerging areas of inquiry, including the association of cough with sleep, exercise, and laryngeal sensory neuropathy, were discussed and new data presented. The urgent need for new and better antitussive drugs was a recurrent theme throughout the meeting, as was perhaps also the sentiment that the most efficient path to that goal would involve collaboration between academia and the pharmaceutical industry. The Second American Cough Conference could not have occurred without the generosity of our major financial sponsor, Reckitt Benckiser, as well as our other providers of significant support, Procter & Gamble and Wyeth Pharmaceuticals. We are grateful to F. Dennis McCool, Editor-in-Chief of Lung, and the publisher, Springer, for again publishing the proceedings of our conference in their journal. We thank the SRxA Institute for Professional Education for cosponsoring the conference along with Medical Education Resources. Finally, we are greatly indebted to the administrative organizers of our meeting— Chris Efessiou, Ph.D., Jenny Mauk, M.Ed., and Veronica Pecnik of Strategic Pharmaceutical Advisors and the SRxA Institute for Professional Education—for their meticulous oversight of every aspect and detail of our conference. The Third American Cough Conference is planned for June 2011. Updates regarding this meeting will be provided, as they become available, on our website: www.cough conference.com.

Characterization of Transient Receptor Potential Melastatin 7 in Bone Marrow Stem Cells

Changes in the intracellular concentrations of Ca2+ and Mg2+ play a significant role in cell growth and differentiation. Mesenchymal stem cells (MSCs) from bone marrow are a potential source for tissue repair due to their ability to differentiate into specialized cells, including bone, fat and muscle. However, the molecular signals controlling the differentiation process remains largely unknown. In this study, we examined whether MSCs express Transient Receptor Potential Melastatin 7 (TRPM7), a member of the TRP family of ion channels and a key pathway for Ca2+ and Mg2+ entry into cells.

De novo expression of Trpm4 initiates secondary hemorrhage in spinal cord injury

The role of transient receptor potential M4 (Trpm4), an unusual member of the Trp family of ion channels, is poorly understood. Using rodent models of spinal cord injury, we studied involvement of Trpm4 in the progressive expansion of secondary hemorrhage associated with capillary fragmentation, the most destructive mechanism of secondary injury in the central nervous system. Trpm4 mRNA and protein were abundantly upregulated in capillaries preceding their fragmentation and formation of petechial hemorrhages. Trpm4 expression in vitro rendered COS-7 cells highly susceptible to oncotic swelling and oncotic death following ATP depletion. After spinal cord injury, in vivo gene suppression in rats treated with Trpm4 antisense or in Trpm4(-/-) mice preserved capillary structural integrity, eliminated secondary hemorrhage, yielded a threefold to fivefold reduction in lesion volume and produced a substantial improvement in neurological function. To our knowledge, this is the first example of a Trp channel that must undergo de novo expression for manifestation of central nervous system pathology.

Expression of ion channels of the TRP family in articular chondrocytes from osteoarthritic patients: changes between native and in vitro propagated chondrocytes

The maintenance of a differentiated chondrocyte phenotype is influenced by several factors of which signal transduction of extracellular stimuli through the cell membrane is of major interest. One important group of membrane-bound proteins which are involved in transmembrane signal transduction are ion channels. Human articular chondrocytes were obtained from osteoarthritic femoral condyles. Cells were released from the surrounding matrix and cultivated under standard conditions. We investigated gene expression of 12 members of the TRP ion channel family of freshly prepared (passage 0; P0) and in vitro propagated human articular chondrocytes (passage 2; P2) using conventional and real-time PCR (RT-PCR). In addition, the protein appearance of four TRP channels was demonstrated by immunofluorescence and western blotting. Chondrocyte differentiation was monitored by quantification of collagen type-II, type-I, and aggrecan gene expression. By conventional PCR, 8 channels could be detected, of which some displayed a heterogeneous PCR pattern. RT-PCR quantification revealed that TRPC1 was expressed on the same level in P0 and P2 chondrocytes while gene expression of TRPC3 and TRPC6 was elevated in passage 2 cells. TRPM5, TRPM7, and TRPV1 displayed an enhanced gene expression in freshly isolated chondrocytes. Immunofluorescence signal intensity of all four investigated TRP proteins was consistent with the corresponding gene expression data. In the present study, a correlation between the appearance of some members of the TRP ion channel family and the state of de-differentiation of osteoarthritic articular chondrocytes was shown. A possible direct involvement in the process of chondrocyte de-differentiation has to be investigated in further studies.