Sex-specific Stone-forming Phenotype in Mice During Hypercalciuria/Urine Alkalinization.

Sex differences in kidney stone formation are well known. Females generally have slightly acidic blood and higher urine pH when compared with males, which makes them more vulnerable to calcium stone formation, yet the mechanism is still unclear. We aimed to examine the role of sex in stone formation during hypercalciuria and urine alkalinization through acetazolamide and calcium gluconate supplementation, respectively, for 4 weeks in wild-type (WT) and moderately hypercalciuric [TRPC3 knockout [KO](-/-)] male and female mice. Our goal was to develop calcium phosphate (CaP) and CaP+ calcium oxalate mixed stones in our animal model to understand the underlying sex-based mechanism of calcium nephrolithiasis. Our results from the analyses of mice urine, serum, and kidney tissues show that female mice (WT and KO) produce more urinary CaP crystals, higher [Ca2+], and pH in urine compared to their male counterparts. We identified a sex-based relationship of stone-forming phenotypes (types of stones) in our mice model following urine alkalization/calcium supplementation, and our findings suggest that female mice are more susceptible to CaP stones under those conditions. Calcification and fibrotic and inflammatory markers were elevated in treated female mice compared with their male counterparts, and more so in TRPC3 KO mice compared with their WT counterparts. Together these findings contribute to a mechanistic understanding of sex-influenced CaP and mixed stone formation that can be used as a basis for determining the factors in sex-related clinical studies.

Qian Yang Yu Yin granule improves hypertensive renal damage: A potential role for TRPC6-CaMKKß-AMPK-mTOR-mediated autophagy.

ETHNOPHARMACOLOGICAL RELEVANCE: Qian Yang Yu Yin granules (QYYYG) have a long history in the treatment of hypertensive renal damage (HRD) in China. Clinical studies have found that QYYYG stabilizes blood pressure and prevents early renal damage. However, the exact mechanism is not entirely clear. AIM OF THE STUDY: To evaluate the therapeutic effect and further explore the therapeutic mechanism of QYYYG against HRD. MATERIALS AND METHODS: The efficacy of QYYYG in treating HRD was assessed in spontaneous hypertension rats (SHR). Renal autophagy and the TRPC6-CaMKKß-AMPK pathway in rats were evaluated. The regulatory role of QYYYG in angiotensin II (Ang II) induced abnormal autophagy in rat podocytes was determined by detecting autophagy-related proteins, intracellular Ca2+ content, and the TRPC6-CaMKKß-AMPK-mTOR pathway expressions. Finally, we established a stable rat podocyte cell line overexpressing TRPC6 and used the cells to verify the regulatory effects of QYYYG. RESULTS: QYYYG alleviated HRD and reversed the abnormal expression of autophagy-related genes in the SHR. In vitro, QYYYG protected against Ang II-induced podocyte damage. Furthermore, treatment of podocytes with QYYYG reversed Ang II-induced autophagy and inhibited Ang II-stimulated TRPC6 activation, Ca2+ influx and activation CaMKKß-AMPK pathway. Overexpression of TRPC6 resulted in pronounced activation of CaMKKß, AMPK, and autophagy induction in rat podocytes, which were significantly attenuated by QYYYG. CONCLUSIONS: The present study suggested that QYYYG may exert its HRD protective effects in part by regulating the abnormal autophagy of podocytes through the TRPC6-CaMKKß-AMPK-mTOR pathway.

Wenyang Huazhuo Fang exerts transient receptor potential cation channel subfamily C member-dependent nephroprotection in a rat model of doxorubicin-induced nephropathy.

OBJECTIVE: To determine the effect of Wenyang Huazhuo Fang (WHF), a Traditional Chinese Medicine decoction, on renal function in a rat model of doxorubicin-induced nephropathy, and to elucidate the underlying mechanism. METHODS: Sprague-Dawley rats were randomly divided into six groups: control, doxorubicin-nephropathy, and prednisone-treated (6.45 mg·kg-1·d－1) doxorubicin nephropathy groups, as well as high- (7.26 g·kg-1·d－1, medium- (2.42 g·kg-1·d－1, and low-dose (0.81 g·kg-1·d－1 WHF-treated doxorubicin-nephropathy groups. The nephropathy rat model was established by two tail vein injections of doxorubicin, followed by prednisone or WHF treatment for 8 weeks. Body weights were monitored and urinary protein was measured every 2 weeks. After the end of the treatment period, the rats were euthanized. Serum biochemical indicators were determined and renal morphological alterations were assessed using histological staining. The expression of transient receptor potential cation channel subfamily C member 6 (TRPC6), stromal interaction molecule 1 (STIM1), and calcium release-activated calcium channel protein 1 (Orai1) was detected using western blotting, and their mRNA levels were examined using quantitative real-time reverse transcription-polymerase chain reaction. RESULTS: WHF treatment was found to significantly ameliorate weight loss, proteinuria, hypoalbuminemia, and dyslipidemia in doxorubicin-nephropathy rats. The protein and mRNA levels of TRPC6, STIM1, and Orai1 were partially, but significantly suppressed by prednisone or WHF treatment. CONCLUSION: Treatment with WHF significantly ameliorates renal injury in a rat model of doxorubicin-induced nephropathy, which could be at least partially related to repression of the TRPC6 pathway.

Cortex Mori Radicis extract promotes neurite outgrowth in diabetic rats by activating PI3K/AKT signaling and inhibiting Ca2+ influx associated with the upregulation of transient receptor potential canonical channel 1.

Cortex Mori Radicis extract (CMR) has various pharmacological properties, such as anti­inflammatory, anti­allergic and anti­hyperglycemic effects. However, the effects and mechanisms of CMR in the neuroregeneration of diabetic peripheral neuropathy (DPN) are unclear. In the present study, the effects of CMR on neurite outgrowth of dorsal root ganglia (DRG) neurons in diabetic rats were investigated and its underlying mechanisms were explored. SD rats were subjected to a high­fat diet with low­dose streptozotocin to induce a Type II diabetes model with peripheral neuropathy. CMR was then applied for four weeks continuously with or without injection of small interfere (si)RNA targeting the transient receptor potential canonical channel 1 (TRPC1) via the tail vein. Blood glucose levels, the number of Nissl bodies, neurite outgrowth and growth cone turning in DRG neurons were evaluated. The expression of TRPC1 protein, Ca2+ influx and activation of the PI3K/AKT signaling pathway were also investigated. The results of the present study showed that CMR significantly lowered blood glucose levels, reversed the loss of Nissl bodies, induced neurite outgrowth and restored the response of the growth cone of DRG neurons in diabetic rats. CMR exerted neurite outgrowth­promoting effects by increasing TRPC1 expression, reducing Ca2+ influx and enhancing AKT phosphorylation. siRNA targeting TRPC1 in the CMR group abrogated its anti­diabetic and neuroregenerative effects, suggesting the involvement of TRPC1 in the biological effects of CMR on DPN.

Ambient and supplemental magnetic fields promote myogenesis via a TRPC1-mitochondrial axis: evidence of a magnetic mitohormetic mechanism.

We show that both supplemental and ambient magnetic fields modulate myogenesis. A lone 10 min exposure of myoblasts to 1.5 mT amplitude supplemental pulsed magnetic fields (PEMFs) accentuated in vitro myogenesis by stimulating transient receptor potential (TRP)-C1-mediated calcium entry and downstream nuclear factor of activated T cells (NFAT)-transcriptional and P300/CBP-associated factor (PCAF)-epigenetic cascades, whereas depriving myoblasts of ambient magnetic fields slowed myogenesis, reduced TRPC1 expression, and silenced NFAT-transcriptional and PCAF-epigenetic cascades. The expression levels of peroxisome proliferator-activated receptor γ coactivator 1α, the master regulator of mitochondriogenesis, was also enhanced by brief PEMF exposure. Accordingly, mitochondriogenesis and respiratory capacity were both enhanced with PEMF exposure, paralleling TRPC1 expression and pharmacological sensitivity. Clustered regularly interspaced short palindromic repeats-Cas9 knockdown of TRPC1 precluded proliferative and mitochondrial responses to supplemental PEMFs, whereas small interfering RNA gene silencing of TRPM7 did not, coinciding with data that magnetoreception did not coincide with the expression or function of other TRP channels. The aminoglycoside antibiotics antagonized and down-regulated TRPC1 expression and, when applied concomitantly with PEMF exposure, attenuated PEMF-stimulated calcium entry, mitochondrial respiration, proliferation, differentiation, and epigenetic directive in myoblasts, elucidating why the developmental potential of magnetic fields may have previously escaped detection. Mitochondrial-based survival adaptations were also activated upon PEMF stimulation. Magnetism thus deploys an authentic myogenic directive that relies on an interplay between mitochondria and TRPC1 to reach fruition.-Yap, J. L. Y., Tai, Y. K., Fröhlich, J., Fong, C. H. H., Yin, J. N., Foo, Z. L., Ramanan, S., Beyer, C., Toh, S. J., Casarosa, M., Bharathy, N., Kala, M. P., Egli, M., Taneja, R., Lee, C. N., Franco-Obregón, A. Ambient and supplemental magnetic fields promote myogenesis via a TRPC1-mitochondrial axis: evidence of a magnetic mitohormetic mechanism.

Novel findings of 18ß-glycyrrhetinic acid on sRAGE secretion through inhibition of transient receptor potential canonical channels in high-glucose environment.

Enhancing soluble receptor for advanced glycation endproducts (sRAGE) is considered as a potent strategy for diabetes therapy. sRAGE secretion is regulated by calcium and transient receptor potential canonical (TRPC) channels. However, the role of TRPC channels in diabetes remains unknown. 18ß-Glycyrrhetinic acid (18ß-GA), produced from liquorice, has shown antidiabetic properties. This study was aimed to investigate the effect of 18ß-GA on sRAGE secretion via TRPC channels in high glucose (HG)-induced THP-1 cells. HG treatment enhanced TRPC3 and TRPC6 expression and consequently caused reactive oxygen species (ROS) accumulation mediated through p47 nicotinamide-adenine dinucleotide phosphate oxidase and inducible nitric oxide synthase (iNOS) associated with uncoupling protein 2 (UCP2) decline and lower sRAGE secretion. Interestingly, 18ß-GA showed the dramatic effects similar to Pyr3 or 2-aminoethyl diphenyl borinate inhibitors and effectively reversed HG-elicited mechanisms including that blocking TRPC3 and TRPC6 protein expressions, suppressing intracellular [Ca2+] concentration, decreasing expressions of ROS, p47s, and iNOS, but increasing UCP2 level and promoting sRAGE secretion. Therefore, 18ß-GA provides a potential implication to diabetes mellitus and its complications.

Social Control of Hypothalamus-Mediated Male Aggression.

How environmental and physiological signals interact to influence neural circuits underlying developmentally programmed social interactions such as male territorial aggression is poorly understood. We have tested the influence of sensory cues, social context, and sex hormones on progesterone receptor (PR)-expressing neurons in the ventromedial hypothalamus (VMH) that are critical for male territorial aggression. We find that these neurons can drive aggressive displays in solitary males independent of pheromonal input, gonadal hormones, opponents, or social context. By contrast, these neurons cannot elicit aggression in socially housed males that intrude in another male's territory unless their pheromone-sensing is disabled. This modulation of aggression cannot be accounted for by linear integration of environmental and physiological signals. Together, our studies suggest that fundamentally non-linear computations enable social context to exert a dominant influence on developmentally hard-wired hypothalamus-mediated male territorial aggression.

Atractylenolide I stimulates intestinal epithelial repair through polyamine-mediated Ca2+ signaling pathway.

BACKGROUND: An impairment of the integrity of the mucosal epithelial barrier can be observed in the course of various gastrointestinal diseases. The migration and proliferation of the intestinal epithelial (IEC-6) cells are essential repair modalities to the healing of mucosal ulcers and wounds. Atractylenolide I (AT-I), one of the major bioactive components in the rhizome of Atractylodes macrocephala Koidz. (AMR), possesses multiple pharmacological activities. This study was designed to investigate the therapeutic effects and the underlying molecular mechanisms of AT-I on gastrointestinal mucosal injury. METHODS: Scratch method with a gel-loading microtip was used to detect IEC-6 cell migration. The real-time cell analyzer (RTCA) system was adopted to evaluate IEC-6 cell proliferation. Intracellular polyamines content was determined using high performance liquid chromatography (HPLC). Flow cytometry was used to measure cytosolic free Ca2+ concentration ([Ca2+]c). mRNA and protein expression of TRPC1 and PLC-γ1 were determined by real-time PCR and Western blotting assay respectively. RESULTS: Treatment of IEC-6 cells with AT-I promoted cell migration and proliferation, increased polyamines content, raised cytosolic free Ca2+ concentration ([Ca2+]c), and enhanced TRPC1 and PLC-γ1 mRNA and protein expression. Depletion of cellular polyamines by DL-a-difluoromethylornithine (DFMO, an inhibitor of polyamine synthesis) suppressed cell migration and proliferation, decreased polyamines content, and reduced [Ca2+]c, which was paralleled by a decrease in TRPC1 and PLC-γ1 mRNA and protein expression in IEC-6 cells. AT-I reversed the effects of DFMO on polyamines content, [Ca2+]c, TRPC1 and PLC-γ1 mRNA and protein expression, and restored IEC-6 cell migration and proliferation to near normal levels. CONCLUSION: Our data demonstrate that AT-I stimulates intestinal epithelial cell migration and proliferation via the polyamine-mediated Ca2+ signaling pathway. Therefore, AT-I may have the potential to be further developed as a promising therapeutic agent to treat diseases associated with gastrointestinal mucosal injury, such as inflammatory bowel disease and peptic ulcer.

Transient receptor potential (TRP) channel function in the reproductive axis.

Transient receptor potential (TRP) channels play important functional roles in the signal transduction machinery of hormone-secreting cells and have recently been implicated in reproductive physiology. While expression studies have demonstrated TRP channel expression at all levels of the hypothalamic-pituitary-gonadal (hpg) axis, functional details about TRP channel action at the level of the individual cells controlling reproduction are just beginning to emerge. Canonical TRP (TRPC) channels are prominently expressed in the reproductive center of the neuroendocrine brain, i.e. in kisspeptin and gonadotropin-releasing hormone (GnRH) neurons. Kisspeptin neurons are depolarized by leptin via activation of TRPC channels and kisspeptin depolarizes GnRH neurons through TRPC4 activation. Recent studies have functionally identified TRPC channels also in gonadotrope cells in the anterior pituitary gland, which secrete gonadotropins in response to GnRH and thus regulate gonadal function. TRP channel expression in these cells exhibits remarkable plasticity and depends on the hormonal status of the animal. Subsequent functional analyses have demonstrated that TRPC5 in gonadotropes contributes to depolarization of the plasma membrane upon GnRH stimulation and increases the intracellular Ca2+ concentration via its own Ca2+ permeability and via the activation of voltage-gated Ca2+ channels. However, conditional gene targeting experiments will be needed to unambiguously dissect the physiological role of TRPC channels in the different cell types of the reproductive axis in vivo.

Transient receptor potential canonical 5 channels plays an essential role in hepatic dyslipidemia associated with cholestasis.

Transient receptor potential canonical 5 (TRPC5), a calcium-permeable, non-selective cation channel is expressed in the periphery, but there is limited knowledge of its regulatory roles in vivo. Endogenous modulators of TRPC5 include a range of phospholipids that have an established role in liver disease, including lysophosphatidylcholine (LPC). Cholestasis is characterized by impairment of excretion of bile acids, leading to elevation of hepatic bile acids. We investigated the contribution of TRPC5 in a murine model of cholestasis. Wild-type (WT) and TRPC5 knock-out (KO) mice were fed a diet supplemented with 0.5% cholic acid (CA) for 21 days. CA-diet supplementation resulted in enlargement of the liver in WT mice, which was ameliorated in TRPC5 KO mice. Hepatic bile acid and lipid content was elevated in WT mice, with a reduction observed in TRPC5 KO mice. Consistently, liver enzymes were significantly increased in cholestatic WT mice and significantly blunted in TRPC5 KO mice. Localized dyslipidaemia, secondary to cholestasis, was investigated utilizing a selected lipid analysis. This revealed significant perturbations in the lipid profile following CA-diet feeding, with increased cholesterol, triglycerides and phospholipids, in WT, but not TRPC5 KO mice. Our results suggest that activation of TRPC5 contributes to the development of cholestasis and associated dyslipidemia. Modulation of TRPC5 activity may present as a novel therapeutic target for liver disease.

Hyperforin/HP-ß-Cyclodextrin Enhances Mechanosensitive Ca2+ Signaling in HaCaT Keratinocytes and in Atopic Skin Ex Vivo Which Accelerates Wound Healing.

Cutaneous wound healing is accelerated by mechanical stretching, and treatment with hyperforin, a major component of a traditional herbal medicine and a known TRPC6 activator, further enhances the acceleration. We recently revealed that this was due to the enhancement of ATP-Ca2+ signaling in keratinocytes by hyperforin treatment. However, the low aqueous solubility and easy photodegradation impede the topical application of hyperforin for therapeutic purposes. We designed a compound hydroxypropyl-ß-cyclodextrin- (HP-ß-CD-) tetracapped hyperforin, which had increased aqueous solubility and improved photoprotection. We assessed the physiological effects of hyperforin/HP-ß-CD on wound healing in HaCaT keratinocytes using live imaging to observe the ATP release and the intracellular Ca2+ increase. In response to stretching (20%), ATP was released only from the foremost cells at the wound edge; it then diffused to the cells behind the wound edge and activated the P2Y receptors, which caused propagating Ca2+ waves via TRPC6. This process might facilitate wound closure, because the Ca2+ response and wound healing were inhibited in parallel by various inhibitors of ATP-Ca2+ signaling. We also applied hyperforin/HP-ß-CD on an ex vivo skin model of atopic dermatitis and found that hyperforin/HP-ß-CD treatment for 24 h improved the stretch-induced Ca2+ responses and oscillations which failed in atopic skin.

Transient Receptor Potential Canonical 3 (TRPC3) Channels Are Required for Hypothalamic Glucose Detection and Energy Homeostasis.

The mediobasal hypothalamus (MBH) contains neurons capable of directly detecting metabolic signals such as glucose to control energy homeostasis. Among them, glucose-excited (GE) neurons increase their electrical activity when glucose rises. In view of previous work, we hypothesized that transient receptor potential canonical type 3 (TRPC3) channels are involved in hypothalamic glucose detection and the control of energy homeostasis. To investigate the role of TRPC3, we used constitutive and conditional TRPC3-deficient mouse models. Hypothalamic glucose detection was studied in vivo by measuring food intake and insulin secretion in response to increased brain glucose level. The role of TRPC3 in GE neuron response to glucose was studied by using in vitro calcium imaging on freshly dissociated MBH neurons. We found that whole-body and MBH TRPC3-deficient mice have increased body weight and food intake. The anorectic effect of intracerebroventricular glucose and the insulin secretory response to intracarotid glucose injection are blunted in TRPC3-deficient mice. TRPC3 loss of function or pharmacological inhibition blunts calcium responses to glucose in MBH neurons in vitro. Together, the results demonstrate that TRPC3 channels are required for the response to glucose of MBH GE neurons and the central effect of glucose on insulin secretion and food intake.

Selective antagonism of TRPA1 produces limited efficacy in models of inflammatory- and neuropathic-induced mechanical hypersensitivity in rats.

The transient receptor potential ankyrin 1 (TRPA1) channel has been implicated in pathophysiological processes that include asthma, cough, and inflammatory pain. Agonists of TRPA1 such as mustard oil and its key component allyl isothiocyanate (AITC) cause pain and neurogenic inflammation in humans and rodents, and TRPA1 antagonists have been reported to be effective in rodent models of pain. In our pursuit of TRPA1 antagonists as potential therapeutics, we generated AMG0902, a potent (IC90 of 300 nM against rat TRPA1), selective, brain penetrant (brain to plasma ratio of 0.2), and orally bioavailable small molecule TRPA1 antagonist. AMG0902 reduced mechanically evoked C-fiber action potential firing in a skin-nerve preparation from mice previously injected with complete Freund's adjuvant, supporting the role of TRPA1 in inflammatory mechanosensation. In vivo target coverage of TRPA1 by AMG0902 was demonstrated by the prevention of AITC-induced flinching/licking in rats. However, oral administration of AMG0902 to rats resulted in little to no efficacy in models of inflammatory, mechanically evoked hypersensitivity; and no efficacy was observed in a neuropathic pain model. Unbound plasma concentrations achieved in pain models were about 4-fold higher than the IC90 concentration in the AITC target coverage model, suggesting that either greater target coverage is required for efficacy in the pain models studied or TRPA1 may not contribute significantly to the underlying mechanisms.

Danshensu protects against ischemia/reperfusion injury and inhibits the apoptosis of H9c2 cells by reducing the calcium overload through the p-JNK-NF-κB-TRPC6 pathway.

Ischemia-reperfusion (I/R) plays an important role in myocardial injury. In the present study, we aimed to examine the protective effects of Danshensu (DSS) against I/R injury and to elucidate the underlying mechanisms. For this purpose, H9c2 cells were cultured in hypoxic solution in a hypoxic incubator for 2 h, and then cultured in a high oxygen incubator for various periods of time and pre-treated with or without DSS, ammonium pyrrolidine dithiocarbamate (PDTC) or SP600125 [a c-Jun N-terminal kinase (JNK) inhibitor]. Cell apoptosis and cytosolic free Ca2+ ([Ca2+]i) levels were analyzed by flow cytometry. The protein expression levels of JNK, phosphorylated (p-)JNK, nuclear factor-κB (NF-κB) and transient receptor potential cation channel, subfamily C, member 6 (TRPC6) were measured by western blot analysis. The mRNA expression levels of JNK were measured by RT-qPCR. The results revealed that TRPC6 protein expression, the cell apoptotic rate and the [Ca2+]i levels increased in a time-dependent manner in the H9c2 cells following the induction of I/R injury. The apoptotic rate and TRPC6 protein expression decreased when the cells were treated with DSS prior to the induction of I/R injury. The knockdown of JNK expression by siRNA decreased the p-JNK and TRPC6 protein expression levels in the H9c2 cells subjected to I/R injury. The protein expression levels of p-JNK and NF-κB in the nucleus increased significantly when the H9c2 cells were subjected to I/R injury, whereas NF-κB expression in the cytoplasm decreased in a time­dependent manner. However, p-JNK, NF-κB and TRPC6 protein expression, the [Ca2+]i level and cell apoptosis decreased when the H9c2 cells were pre-treated with DSS or SP600125. Therefore, our data suggest that DSS prevents myocardial I/R injury by inhibiting p-JNK activation and NF-κB translocation, which potentially upregulate TRPC6 expression, increase the [Ca2+]i level, and result in the apoptosis of H9c2 cells.

Complementary roles of KCa3.1 channels and ß1-integrin during alveolar epithelial repair.

BACKGROUND: Extensive alveolar epithelial injury and remodelling is a common feature of acute lung injury and acute respiratory distress syndrome (ARDS) and it has been established that epithelial regeneration, and secondary lung oedema resorption, is crucial for ARDS resolution. Much evidence indicates that K(+) channels are regulating epithelial repair processes; however, involvement of the KCa3.1 channels in alveolar repair has never been investigated before. RESULTS: Wound-healing assays demonstrated that the repair rates were increased in primary rat alveolar cell monolayers grown on a fibronectin matrix compared to non-coated supports, whereas an anti-ß1-integrin antibody reduced it. KCa3.1 inhibition/silencing impaired the fibronectin-stimulated wound-healing rates, as well as cell migration and proliferation, but had no effect in the absence of coating. We then evaluated a putative relationship between KCa3.1 channel and the migratory machinery protein ß1-integrin, which is activated by fibronectin. Co-immunoprecipitation and immunofluorescence experiments indicated a link between the two proteins and revealed their cellular co-distribution. In addition, we demonstrated that KCa3.1 channel and ß1-integrin membrane expressions were increased on a fibronectin matrix. We also showed increased intracellular calcium concentrations as well as enhanced expression of TRPC4, a voltage-independent calcium channel belonging to the large TRP channel family, on a fibronectin matrix. Finally, wound-healing assays showed additive effects of KCa3.1 and TRPC4 inhibitors on alveolar epithelial repair. CONCLUSION: Taken together, our data demonstrate for the first time complementary roles of KCa3.1 and TRPC4 channels with extracellular matrix and ß1-integrin in the regulation of alveolar repair processes.

TRPC3 contributes to regulation of cardiac contractility and arrhythmogenesis by dynamic interaction with NCX1.

AIM: TRPC3 is a non-selective cation channel, which forms a Ca2+ entry pathway involved in cardiac remodelling. Our aim was to analyse acute electrophysiological and contractile consequences of TRPC3 activation in the heart. METHODS AND RESULTS: We used a murine model of cardiac TRPC3 overexpression and a novel TRPC3 agonist, GSK1702934A, to uncover (patho)physiological functions of TRPC3. GSK1702934A induced a transient, non-selective conductance and prolonged action potentials in TRPC3-overexpressing myocytes but lacked significant electrophysiological effects in wild-type myocytes. GSK1702934A transiently enhanced contractility and evoked arrhythmias in isolated Langendorff hearts from TRPC3-overexpressing but not wild-type mice. Interestingly, pro-arrhythmic effects outlasted TRPC3 current activation, were prevented by enhanced intracellular Ca2+ buffering, and suppressed by the NCX inhibitor 3',4'-dichlorobenzamil hydrochloride. GSK1702934A substantially promoted NCX currents in TRPC3-overexpressing myocytes. The TRPC3-dependent electrophysiologic, pro-arrhythmic, and inotropic actions of GSK1702934A were mimicked by angiotensin II (AngII). Immunocytochemistry demonstrated colocalization of TRPC3 with NCX1 and disruption of local interaction upon channel activation by either GSK1702934A or AngII. CONCLUSION: Cardiac TRPC3 mediates Ca2+ and Na+ entry in proximity of NCX1, thereby elevating cellular Ca2+ levels and contractility. Excessive activation of TRPC3 is associated with transient cellular Ca2+ overload, spatial uncoupling between TRPC3 and NCX1, and arrhythmogenesis. We propose TRPC3-NCX micro/nanodomain communication as determinant of cardiac contractility and susceptibility to arrhythmogenic stimuli.

Protonophore properties of hyperforin are essential for its pharmacological activity.

Hyperforin is a pharmacologically active component of the medicinal plant Hypericum perforatum (St. John's wort), recommended as a treatment for a range of ailments including mild to moderate depression. Part of its action has been attributed to TRPC6 channel activation. We found that hyperforin induces TRPC6-independent H(+) currents in HEK-293 cells, cortical microglia, chromaffin cells and lipid bilayers. The latter demonstrates that hyperforin itself acts as a protonophore. The protonophore activity of hyperforin causes cytosolic acidification, which strongly depends on the holding potential, and which fuels the plasma membrane sodium-proton exchanger. Thereby the free intracellular sodium concentration increases and the neurotransmitter uptake by Na(+) cotransport is inhibited. Additionally, hyperforin depletes and reduces loading of large dense core vesicles in chromaffin cells, which requires a pH gradient in order to accumulate monoamines. In summary the pharmacological actions of the "herbal Prozac" hyperforin are essentially determined by its protonophore properties shown here.

Mechanosensitive ATP release from hemichannels and Ca²âº influx through TRPC6 accelerate wound closure in keratinocytes.

Cutaneous wound healing is accelerated by exogenous mechanical forces and is impaired in TRPC6-knockout mice. Therefore, we designed experiments to determine how mechanical force and TRPC6 channels contribute to wound healing using HaCaT keratinocytes. HaCaT cells were pretreated with hyperforin, a major component of a traditional herbal medicine for wound healing and also a TRPC6 activator, and cultured in an elastic chamber. At 3 h after scratching the confluent cell layer, the ATP release and intracellular Ca(2+) increases in response to stretching (20%) were live-imaged. ATP release was observed only in cells at the frontier facing the scar. The diffusion of released ATP caused intercellular Ca(2+) waves that propagated towards the rear cells in a P2Y-receptor-dependent manner. The Ca(2+) response and wound healing were inhibited by ATP diphosphohydrolase apyrase, the P2Y antagonist suramin, the hemichannel blocker CBX and the TRPC6 inhibitor diC8-PIP2. Finally, the hemichannel-permeable dye calcein was taken up only by ATP-releasing cells. These results suggest that stretch-accelerated wound closure is due to the ATP release through mechanosensitive hemichannels from the foremost cells and the subsequent Ca(2+) waves mediated by P2Y and TRPC6 activation.

Nonpsychotropic plant cannabinoids, cannabidivarin (CBDV) and cannabidiol (CBD), activate and desensitize transient receptor potential vanilloid 1 (TRPV1) channels in vitro: potential for the treatment of neuronal hyperexcitability.

Epilepsy is the most common neurological disorder, with over 50 million people worldwide affected. Recent evidence suggests that the transient receptor potential cation channel subfamily V member 1 (TRPV1) may contribute to the onset and progression of some forms of epilepsy. Since the two nonpsychotropic cannabinoids cannabidivarin (CBDV) and cannabidiol (CBD) exert anticonvulsant activity in vivo and produce TRPV1-mediated intracellular calcium elevation in vitro, we evaluated the effects of these two compounds on TRPV1 channel activation and desensitization and in an in vitro model of epileptiform activity. Patch clamp analysis in transfected HEK293 cells demonstrated that CBD and CBDV dose-dependently activate and rapidly desensitize TRPV1, as well as TRP channels of subfamily V type 2 (TRPV2) and subfamily A type 1 (TRPA1). TRPV1 and TRPV2 transcripts were shown to be expressed in rat hippocampal tissue. When tested on epileptiform neuronal spike activity in hippocampal brain slices exposed to a Mg(2+)-free solution using multielectrode arrays (MEAs), CBDV reduced both epileptiform burst amplitude and duration. The prototypical TRPV1 agonist, capsaicin, produced similar, although not identical effects. Capsaicin, but not CBDV, effects on burst amplitude were reversed by IRTX, a selective TRPV1 antagonist. These data suggest that CBDV antiepileptiform effects in the Mg(2+)-free model are not uniquely mediated via activation of TRPV1. However, TRPV1 was strongly phosphorylated (and hence likely sensitized) in Mg(2+)-free solution-treated hippocampal tissue, and both capsaicin and CBDV caused TRPV1 dephosphorylation, consistent with TRPV1 desensitization. We propose that CBDV effects on TRP channels should be studied further in different in vitro and in vivo models of epilepsy.

A rat knockout model implicates TRPC4 in visceral pain sensation.

Acute and chronic pain resulting from injury, surgery, or disease afflicts >100 million Americans each year, having a severe impact on mood, mental health, and quality of life. The lack of structural and functional information for most ion channels, many of which play key roles in the detection and transmission of noxious stimuli, means that there remain unidentified therapeutic targets for pain management. This study focuses on the transient receptor potential canonical subfamily 4 (TRPC4) ion channel, which is involved in the tissue-specific and stimulus-dependent regulation of intracellular Ca²âº signaling. Rats with a transposon-mediated TRPC4-knockout mutation displayed tolerance to visceral pain induced by colonic mustard oil (MO) exposure, but not somatic or neuropathic pain stimuli. Moreover, wild-type rats treated with a selective TRPC4 antagonist (ML-204) prior to MO exposure mimicked the behavioral responses observed in TRPC4-knockout rats. Significantly, ML-204 inhibited visceral pain-related behavior in a dose-dependent manner without noticeable adverse effects. These data provide evidence that TRPC4 is required for detection and/or transmission of colonic MO visceral pain sensation. In the future, inhibitors of TRPC4 signaling may provide a highly promising path for the development of first-in-class therapeutics for this visceral pain, which may have fewer side effects and less addictive potential than opioid derivatives.