TRPC3

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Jongyun Myeong - One of the best experts on this subject based on the ideXlab platform.

  • TRPC1 as a negative regulator for TRPC4 and TRPC5 channels
    Pflügers Archiv - European Journal of Physiology, 2019
    Co-Authors: Jinsung Kim, Juyeon Ko, Jongyun Myeong, Misun Kwak, Chansik Hong, Insuk So
    Abstract:

    Transient receptor potential canonical (TRPC) channels are calcium permeable, non-selective cation channels with wide tissue-specific distribution. Among 7 TRPC channels, TRPC 1/4/5 and TRPC3/6/7 are subdivided based on amino acid sequence homology. TRPC4 and TRPC5 channels exhibit cationic current with homotetrameric form, but they also form heterotetrameric channel such as TRPC1/4 or TRPC1/5 once TRPC1 is incorporated. The expression of TRPC1 is ubiquitous whereas the expressions of TRPC4 and TRPC5 are rather focused in nervous system. With the help of conditional knock-out of TPRC1, 4 and/or 5 genes, TRPC channels made of these constituents are reported to be involved in various pathophysiological functions such as seizure, anxiety-like behaviour, fear, Huntington’s disease, Parkinson’s disease and many others. In heterologous expression system, many issues such as activation mechanism, stoichiometry and relative cation permeabilites of homomeric or heteromeric channels have been addressed. In this review, we discussed the role of TRPC1 channel per se in plasma membrane, role of TRPC1 in heterotetrameric conformation (TRPC1/4 or TRPC1/5) and relationship between TRPC1/4/5 channels, calcium influx and voltage-gated calcium channels.

  • differential pi 4 5 p 2 sensitivities of trpc4 c5 homomeric and trpc1 4 c1 5 heteromeric channels
    Scientific Reports, 2019
    Co-Authors: Jongyun Myeong, Young-cheul Shin
    Abstract:

    Transient receptor potential canonical (TRPC) 4 and TRPC5 channels are modulated by the Gαq-PLC pathway. Since phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) maintains TRPC4 and TRPC5 channel function, the Gαq-PLC pathway inhibits channel activity by depleting PI(4,5)P2. Here we investigated the difference in PI(4,5)P2 sensitivity between homomeric and heteromeric TRPC channels. First, by using a Danio rerio voltage-sensing phosphatase (DrVSP), we show that PI(4,5)P2 dephosphorylation robustly inhibits TRPC4α, TRPC4β, and TRPC5 homotetramer currents and also TRPC1/4α, TRPC1/4β, and TRPC1/5 heterotetramer currents. Secondly, sensitivity of channels to PI(4,5)P2 dephosphorylation was suggested through the usage of FRET in combination with patch clamping. The sensitivity increased in the sequence TRPC4β < TRPC4α < TRPC5 in homotetramers, whereas when forming heterotetramers with TRPC1, the sensitivity was approximately equal between the channels. Thirdly, we determined putative PI(4,5)P2 binding sites based on a TRPC4 prediction model. By neutralization of basic residues, we identified putative PI(4,5)P2 binding sites because the mutations reduced FRET to a PI(4,5)P2 sensor and reduced the current amplitude. Therefore, one functional TRPC4 has 8 pockets with the two main binding regions; K419, K664/R511, K518, H630. We conclude that TRPC1 channel function as a regulator in setting PI(4,5)P2 affinity for TRPC4 and TRPC5 that changes PI(4,5)P2 sensitivity.

  • Differential PI(4,5)P2 sensitivities of TRPC4, C5 homomeric and TRPC1/4, C1/5 heteromeric channels
    Nature Publishing Group, 2019
    Co-Authors: Jongyun Myeong, Young-cheul Shin
    Abstract:

    Abstract Transient receptor potential canonical (TRPC) 4 and TRPC5 channels are modulated by the Gαq-PLC pathway. Since phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) maintains TRPC4 and TRPC5 channel function, the Gαq-PLC pathway inhibits channel activity by depleting PI(4,5)P2. Here we investigated the difference in PI(4,5)P2 sensitivity between homomeric and heteromeric TRPC channels. First, by using a Danio rerio voltage-sensing phosphatase (DrVSP), we show that PI(4,5)P2 dephosphorylation robustly inhibits TRPC4α, TRPC4β, and TRPC5 homotetramer currents and also TRPC1/4α, TRPC1/4β, and TRPC1/5 heterotetramer currents. Secondly, sensitivity of channels to PI(4,5)P2 dephosphorylation was suggested through the usage of FRET in combination with patch clamping. The sensitivity increased in the sequence TRPC4β 

  • the interaction domains of transient receptor potential canonical trpc 1 4 and trpc1 5 heteromultimeric channels
    Biochemical and Biophysical Research Communications, 2016
    Co-Authors: Jongyun Myeong, Kyu Pil Lee, Chansik Hong, Dongki Yang, Ju Hong Jeon
    Abstract:

    Abstract Transient receptor potential canonical (TRPC) family contains a non-selective cation channel, and four TRPC subunits form a functional tetrameric channel. TRPC4/5 channels form not only the homotetrameric channel but also a heterotetrameric channel with TRPC1. We investigated the interaction domain required for TRPC1/4 or TRPC1/5 heteromultimeric channels using FRET and the patch-clamp technique. TRPC1 only localized at the plasma membrane (PM) when it was coexpressed with TRPC4 or TRPC5. The TRPC1/4 or TRPC1/5 heteromultimeric showed the typical outward rectifying I/V curve. When TRPC1 and TRPC4 form a heteromeric channel, the N-terminal coiled-coil domain (CCD) and C-terminal 725–745 region of TRPC1 interact with the N-terminal CCD and C-terminal 700–728 region of TRPC4. However, when TRPC1 and TRPC5 form a heteromeric channel, the N-terminal CCD and C-terminal 673–725 region of TRPC1 interact with the N-terminal CCD and C-terminal 707–735 region of TRPC5. In conclusion, the N-terminal CCD of TRPC channels is essential for the heteromultimeric structure of TRPC channels, whereas specific C-terminal regions are required for unique heteromerization between subgroups of TRPC channels.

  • isoform and receptor specific channel property of canonical transient receptor potential trpc 1 4 channels
    Pflügers Archiv: European Journal of Physiology, 2014
    Co-Authors: Jinsung Kim, Jongyun Myeong, Misun Kwak, Chansik Hong, Ju Hong Jeon, Jae Pyo Jeon, Jinhong Wie, Sung Young Kim, Hyunjin Kim
    Abstract:

    Transient receptor potential canonical (TRPC) 1, the first mammalian homologue of Drosophila trp gene, is distributed widely in mammalian cells and is involved in many physiological functions. TRPC1 is reported to be functional following heteromeric formation with other TRPC channels such as TRPC4 or TRPC5. It is known that the composition of this widely distributed TRPC1 is far from simple; functionality of such channels has been highly controversial. Furthermore, TRPC1 gene is known to have two splicing variants; one encodes long (TRPC1α) and the other encodes short (TRPC1β) TRPC1 isoforms, respectively. In this study, we examined the functionality of TRPC1/4 channels using various activation systems. Gq/11-coupled receptor (e.g., M1 or M3 receptors) stimulation significantly increased TRPC1α/4 currents but induced mild activation of TRPC1β/4. In addition, when expressed with TRPC4, TRPC1α acted as a pore-constituting subunit and not a β ancillary subunit. Multimerized with TRPC4, TRPC1α also generated strong pore field strength. We also found that Gi/o-coupled receptor (e.g., M2 receptor) stimulation was insufficient to activate TRPC1α/4 and TRPC1β/4 channels but selectively activated TRPC4 homomeric channels. These findings demonstrate that TRPC1/4 channel shows dynamic gating property depending on TRPC1 isoform subtypes and receptor stimulation system. Therefore, careful discrimination of the specificity of TRPC1 isoforms and upstream activation system is important in thorough understanding of TRPC1 and TRPC1/4 channels.

Lutz Birnbaumer - One of the best experts on this subject based on the ideXlab platform.

  • trpc1 and TRPC3 dependent ca2 signaling in mouse cortical astrocytes affects injury evoked astrogliosis in vivo
    Glia, 2017
    Co-Authors: Thabet Belkacemi, Lutz Birnbaumer, Alexander Niermann, Laura Hofmann, Ulrich Wissenbach, Petra Leidinger, Christina Backes, Eckart Meese, Andreas Keller
    Abstract:

    Following brain injury astrocytes change into a reactive state, proliferate and grow into the site of lesion, a process called astrogliosis, initiated and regulated by changes in cytoplasmic Ca2+ . Transient receptor potential canonical (TRPC) channels may contribute to Ca2+ influx but their presence and possible function in astrocytes is not known. By RT-PCR and RNA sequencing we identified transcripts of Trpc1, Trpc2, TRPC3, and Trpc4 in FACS-sorted glutamate aspartate transporter (GLAST)-positive cultured mouse cortical astrocytes and subcloned full-length Trpc1 and TRPC3 cDNAs from these cells. Ca2+ entry in cortical astrocytes depended on TRPC3 and was increased in the absence of Trpc1. After co-expression of Trpc1 and TRPC3 in HEK-293 cells both proteins co-immunoprecipitate and form functional heteromeric channels, with TRPC1 reducing TRPC3 activity. In vitro, lack of TRPC3 reduced astrocyte proliferation and migration whereas the TRPC3 gain-of-function moonwalker mutation and Trpc1 deficiency increased astrocyte migration. In vivo, astrogliosis and cortex edema following stab wound injury were reduced in TRPC3-/- but increased in Trpc1-/- mice. In summary, our results show a decisive contribution of TRPC3 to astrocyte Ca2+ signaling, which is even augmented in the absence of Trpc1, in particular following brain injury. Targeted therapies to reduce TRPC3 channel activity in astrocytes might therefore be beneficial in traumatic brain injury.

  • deletion of diacylglycerol responsive trpc genes attenuates diabetic nephropathy by inhibiting activation of the tgfβ1 signaling pathway
    American Journal of Translational Research, 2017
    Co-Authors: Benju Liu, Lutz Birnbaumer, Yanhong Liao
    Abstract:

    TRPC6 plays a critical role in proteinuric kidney diseases, and TRPC3 is involved in tubulointerstitial damage and renal fibrosis in obstructed kidneys. Podocyte loss is a characteristic event in diabetic nephropathy (DN). The aim of this study was to examine whether deletion of the closely related diacylglycerol (DAG)-responsive TRPCs in mice (TRPC3/6/7-/-) affects diabetes-induced renal dysfunction and podocyte loss. We compared urine volume, kidney hypertrophy, glomerular enlargement, albuminuria and podocyte loss between wild type (WT) and TRPC3/6/7-/- diabetic mice. Finally, we examined whether the TGFβ1 signaling pathway is changed in diabetic WT and TRPC3/6/7-/- mice. TRPC6 protein in the renal cortex was increased in WT diabetic mice. High glucose (HG) treatment increased TRPC6 expression in human podocytes. TRPC3 protein, however, was not altered in either diabetic mice or HG-treated human podocytes. Although diabetic WT and TRPC3/6/7-/- mice had similar levels of hyperglycemia, the TRPC3/6/7-/- diabetic mice showed less polyuria, kidney hypertrophy, glomerular enlargement, albuminuria, and had lost less podocytes compared with WT diabetic mice. In addition, we observed decreased expression of anti-apoptotic Bcl2 and increased expression of pro-apoptotic cleaved caspase 3 in WT diabetic mice, but such changes were not significant in TRPC3/6/7-/- diabetic mice. Western blot and immunohistochemistry revealed that TGFβ1, p-Smad2/3, and fibronectin were upregulated in WT diabetic mice; however, expression of these signaling molecules was not changed in TRPC3/6/7-/- diabetic mice. In conclusion, deletion of DAG-responsive TRPCs attenuates diabetic renal injury via inhibiting the upregulation of TGFβ1 signaling in diabetic kidneys.

  • the contribution of trpc1 TRPC3 trpc5 and trpc6 to touch and hearing
    Neuroscience Letters, 2016
    Co-Authors: Jane E Sexton, Joel Abramowitz, Lutz Birnbaumer, Terri Desmonds, Kathryn Quick, Ruth Taylor, Andy Forge, Corne J Kros, John Wood
    Abstract:

    Transient receptor potential channels have diverse roles in mechanosensation. Evidence is accumulating that members of the canonical subfamily of TRP channels (TRPC) are involved in touch and hearing. Characteristic features of TRP channels include their high structural homology and their propensity to form heteromeric complexes which suggests potential functional redundancy. We previously showed that TRPC3 and TRPC6 double knockout animals have deficits in light touch and hearing whilst single knockouts were apparently normal. We have extended these studies to analyse deficits in global quadruple TRPC1, 3, 5 and 6 null mutant mice. We examined both touch and hearing in behavioural and electrophysiological assays, and provide evidence that the quadruple knockout mice have larger deficits than the TRPC3 TRPC6 double knockouts. Mechano-electrical transducer currents of cochlear outer hair cells were however normal. This suggests that TRPC1, TRPC3, TRPC5 and TRPC6 channels contribute to cutaneous and auditory mechanosensation in a combinatorial manner, but have no direct role in cochlear mechanotransduction.

  • evidence for functional coupling of cgmp cgki signalling and trpc channels in endothelium but not in vascular smooth muscle
    BMC Clinical Pharmacology, 2013
    Co-Authors: Florian Loga, Lutz Birnbaumer, Marc Freichel, Veit Flockerzi, Alexander Dietrich, Katrin Domes, Franz Hofmann, Jorg W Wegener
    Abstract:

    Background Signaling via cGMP-dependent protein kinase I (cGKI) is the major pathway in vascular smooth muscle (SM), by which endothelial NO regulates vascular tone. Recent evidence suggests that canonical transient receptor potential (TRPC) channels are targets of cGKI in SM and mediate the relaxant effects of cGMP signaling. We tested this concept by investigating the role of cGMP/cGKI signaling on vascular tone and peripheral resistance using Trpc6, TRPC3, TRPC3/6, Trpc1/3/6, and SM-specific cGKI (sm-cGKI) mice.

  • intrinsic phototransduction persists in melanopsin expressing ganglion cells lacking diacylglycerol sensitive trpc subunits
    European Journal of Neuroscience, 2011
    Co-Authors: Claudio E Perezleighton, Tiffany M. Schmidt, Joel Abramowitz, Lutz Birnbaumer, Paulo Kofuji
    Abstract:

    In mammals, intrinsically photosensitive retinal ganglion cells (ipRGCs) mediate various non-image-forming photic responses such as circadian photoentrainment, pupillary light reflex, and pineal melatonin suppression. ipRGCs directly respond to environmental light by activation of the photopigment melanopsin followed by the opening of an unidentified cation-selective channel. Studies in heterologous expression systems and in the native retina have strongly implicated diacylglycerol-sensitive transient receptor potential channels containing TRPC3, TRPC6, and TRPC7 subunits in melanopsin-evoked depolarization. Here we show that melanopsin-evoked electrical responses largely persist in ipRGCs recorded from early postnatal (P6-P8) and adult (P22-P50) mice lacking expression of functional TRPC3, TRPC6, or TRPC7 subunits. Multielectrode array recordings performed at P6-P8 stages under conditions that prevent influences from rod/cone photoreceptors show comparable light sensitivity for the melanopsin-evoked responses in these mutant mouse lines in comparison to wild-type mice. Patch-clamp recordings from adult mouse ipRGCs lacking TRPC3 or TRPC7 subunits show intrinsic light-evoked responses equivalent to those recorded in wild-type mice. Persistence of intrinsic light-evoked responses was also noted in ipRGCs lacking TRPC6 subunits, however of significantly smaller magnitudes. These results demonstrate that the melanopsin-evoked depolarization in ipRGCs is not mediated by either TRPC3, TRPC6, or TRPC7 channel subunits alone. They also suggest that the melanopsin signaling pathway includes TRPC6-containing heteromeric channels in mature retinas.

Michael Schaefer - One of the best experts on this subject based on the ideXlab platform.

  • direct activation of TRPC3 channels by the antimalarial agent artemisinin
    Cells, 2020
    Co-Authors: Nicole Urban, Michael Schaefer
    Abstract:

    (1) Background: Members of the TRPC3/TRPC6/TRPC7 subfamily of canonical transient receptor potential (TRP) channels share an amino acid similarity of more than 80% and can form heteromeric channel complexes. They are directly gated by diacylglycerols in a protein kinase C-independent manner. To assess TRPC3 channel functions without concomitant protein kinase C activation, direct activators are highly desirable. (2) Methods: By screening 2000 bioactive compounds in a Ca2+ influx assay, we identified artemisinin as a TRPC3 activator. Validation and characterization of the hit was performed by applying fluorometric Ca2+ influx assays and electrophysiological patch-clamp experiments in heterologously or endogenously TRPC3-expressing cells. (3) Results: Artemisinin elicited Ca2+ entry through TRPC3 or heteromeric TRPC3:TRPC6 channels, but did not or only weakly activated TRPC6 and TRPC7. Electrophysiological recordings confirmed the reversible and repeatable TRPC3 activation by artemisinin that was inhibited by established TRPC3 channel blockers. Rectification properties and reversal potentials were similar to those observed after stimulation with a diacylglycerol mimic, indicating that artemisinin induces a similar active state as the physiological activator. In rat pheochromocytoma PC12 cells that endogenously express TRPC3, artemisinin induced a Ca2+ influx and TRPC3-like currents. (4) Conclusions: Our findings identify artemisinin as a new biologically active entity to activate recombinant or native TRPC3-bearing channel complexes in a membrane-confined fashion.

  • a benzothiadiazine derivative and methylprednisolone are novel and selective activators of transient receptor potential canonical 5 trpc5 channels
    Cell Calcium, 2017
    Co-Authors: Holger Beckmann, Nicole Urban, Kerstin Hill, Julia Richter, Horst Lemoine, Michael Schaefer
    Abstract:

    The transient receptor potential canonical channel 5 (TRPC5) is a Ca2+-permeable ion channel, which is predominantly expressed in the brain. TRPC5-deficient mice exhibit a reduced innate fear response and impaired motor control. In addition, outgrowth of hippocampal and cerebellar neurons is retarded by TRPC5. However, pharmacological evidence of TRPC5 function on cellular or organismic levels is sparse. Thus, there is still a need for identifying novel and efficient TRPC5 channel modulators. We, therefore, screened compound libraries and identified the glucocorticoid methylprednisolone and N-[3-(adamantan-2-yloxy)propyl]-3-(6-methyl-1,1-dioxo-2H-1λ6,2,4-benzothiadiazin-3-yl)propanamide (BTD) as novel TRPC5 activators. Comparisons with closely related chemical structures from the same libraries indicate important substructures for compound efficacy. Methylprednisolone activates TRPC5 heterologously expressed in HEK293 cells with an EC50 of 12μM, while BTD-induced half-maximal activation is achieved with 5-fold lower concentrations, both in Ca2+ assays (EC50=1.4μM) and in electrophysiological whole cell patch clamp recordings (EC50=1.3 μM). The activation resulting from both compounds is long lasting, reversible and sensitive to clemizole, a recently established TRPC5 inhibitor. No influence of BTD on homotetrameric members of the remaining TRPC family was observed. On the main sensory TRP channels (TRPA1, TRPV1, TRPM3, TRPM8) BTD exerts only minor activity. Furthermore, BTD can activate heteromeric channel complexes consisting of TRPC5 and its closest relatives TRPC1 or TRPC4, suggesting a high selectivity of BTD for channel complexes bearing at least one TRPC5 subunit.

  • novel pharmacological trpc inhibitors block hypoxia induced vasoconstriction
    Cell Calcium, 2012
    Co-Authors: Nicole Urban, Kerstin Hill, Liming Wang, Wolfgang M Kuebler, Michael Schaefer
    Abstract:

    The Ca(2+)-permeable, nonselective cation channel TRPC6 is gated via phospholipase C-activating receptors and has recently been implicated in hypoxia-induced pulmonary vasoconstriction (HPV), idiopathic pulmonary hypertension and focal segmental glomerulosclerosis (FSGS). Therefore, TRPC6 is a promising target for pharmacological interference. To identify and develop TRPC6-blocking compounds, we screened the Chembionet library, a collection of 16,671 chemically diverse drug-like compounds, for biological activity to prevent the 1-oleoyl-2-acetyl-sn-glycerol-triggered Ca(2+) influx in a stably transfected HEK(TRPC6-YFP) cell line. Hits were validated and characterised by fluorometric and electrophysiological methods. Six compounds displayed inhibitory potency at low micromolar concentrations, lack of cytotoxicity and blocked the receptor-dependent mode of TRPC6 activation. The specificity was tested towards closely (TRPC3 and TRPC7) and more distantly related TRP channels. One of the compounds, 8009-5364, displayed a 2.5-fold TRPC6-selectivity compared to TRPC3, and almost no inhibition of TRPC7 or the other TRP channels tested. Block of native TRPC3/6-like responses was confirmed in dissociated pulmonary artery smooth muscle cells. Two non-polar blockers effectively suppressed the HPV responses in the perfused mouse lung model. We conclude that pharmacological targeting of TRPC6 is feasible and provide a promising concept to treat pulmonary diseases that are characterised by excessive hypoxic vasoconstriction.

  • TRPC4 and TRPC5: receptor-operated Ca2+-permeable nonselective cation channels.
    Cell calcium, 2003
    Co-Authors: Tim D Plant, Michael Schaefer
    Abstract:

    The seven mammalian channels from the classical (TRPC) subfamily of transient receptor potential (TRP) channels are thought to be receptor-operated cation channels activated in a phospholipase C (PLC)-dependent manner. Based on sequence similarity, TRPC channels can be divided into four subgroups. Group 4 comprises TRPC4 and TRPC5, and is most closely related to group 1 (TRPC1). The functional properties observed following heterologous expression of TRPC4 or TRPC5 in mammalian cells are contradictory and, therefore, controversial. In our hands, and in several independent studies, both channels, probably as homotetramers, form receptor-operated, Ca2+-permeable, nonselective cation channels activated independently of inositol 1,4,5-trisphosphate (InsP(3)) receptor activation or Ca2+ store-depletion. As heteromultimers with TRPC1, TRPC4 and TRPC5 form receptor-operated, Ca2+-permeable, nonselective cation channels with biophysical properties distinct from homomeric TRPC4 or TRPC5. In other studies, TRPC4 and TRPC5 have been shown to be store-operated channels, with moderate to high Ca2+ permeabilities. At present there is no clear explanation for these major differences in functional properties. To date, little is known as to which native cation channels are formed by TRPC4 and TRPC5. Endothelial cells from TRPC4(-/-) mice lack a highly Ca2+-permeable, store-dependent current, and data support a role for TRPC4 in endothelium-mediated vasorelaxation. A similar current in adrenal cortical cells is reduced by TRPC4 antisense. From similarities in the properties of the currents and expression of appropriate isoforms in the tissues, it is likely that heteromultimers of TRPC1 and TRPC4 or TRPC5 form receptor-operated nonselective cation channels in central neurones, and that TRPC4 contributes to nonselective cation channels in intestinal smooth muscle.

  • Subunit composition of mammalian transient receptor potential channels in living cells
    Proceedings of the National Academy of Sciences of the United States of America, 2002
    Co-Authors: Thomas Hofmann, Michael Schaefer, Günter Schultz, Thomas Gudermann
    Abstract:

    Hormones, neurotransmitters, and growth factors give rise to calcium entry via receptor-activated cation channels that are activated downstream of phospholipase C activity. Members of the transient receptor potential channel (TRPC) family have been characterized as molecular substrates mediating receptor-activated cation influx. TRPC channels are assumed to be composed of multiple TRPC proteins. However, the cellular principles governing the assembly of TRPC proteins into homo- or heteromeric ion channels still remain elusive. By pursuing four independent experimental approaches—i.e., subcellular cotrafficking of TRPC subunits, differential functional suppression by dominant-negative subunits, fluorescence resonance energy transfer between labeled TRPC subunits, and coimmunoprecipitation—we investigate the combinatorial rules of TRPC assembly. Our data show that (i) TRPC2 does not interact with any known TRPC protein and (ii) TRPC1 has the ability to form channel complexes together with TRPC4 and TRPC5. (iii) All other TRPCs exclusively assemble into homo- or heterotetramers within the confines of TRPC subfamilies—e.g., TRPC4/5 or TRPC3/6/7. The principles of TRPC channel formation offer the conceptual framework to assess the physiological role of distinct TRPC proteins in living cells.

Donald L Gill - One of the best experts on this subject based on the ideXlab platform.

  • role of endogenous trpc6 channels in ca2 signal generation in a7r5 smooth muscle cells
    Journal of Biological Chemistry, 2005
    Co-Authors: Jonathan Soboloff, Maria A Spassova, Natalia Cuesta, Donald L Gill
    Abstract:

    The ubiquitously expressed canonical transient receptor potential (TRPC) ion channels are considered important in Ca2+ signal generation, but their mechanisms of activation and roles remain elusive. Whereas most studies have examined overexpressed TRPC channels, we used molecular, biochemical, and electrophysiological approaches to assess the expression and function of endogenous TRPC channels in A7r5 smooth muscle cells. Real time PCR and Western analyses reveal TRPC6 as the only member of the diacylglycerol-responsive TRPC3/6/7 subfamily of channels expressed at significant levels in A7r5 cells. TRPC1, TRPC4, and TRPC5 were also abundant. An outwardly rectifying, nonselective cation current was activated by phospholipase C-coupled vasopressin receptor activation or by the diacylglycerol analogue, oleoyl-2-acetyl-sn-glycerol (OAG). Introduction of TRPC6 small interfering RNA sequences into A7r5 cells by electroporation led to 90% reduction of TRPC6 transcript and 80% reduction of TRPC6 protein without any detectable compensatory changes in the expression of other TRPC channels. The OAG-activated nonselective cation current was similarly reduced by TRPC6 RNA interference. Intracellular Ca2+ measurements using fura-2 revealed that thapsigargin-induced store-operated Ca2+ entry was unaffected by TRPC6 knockdown, whereas vasopressin-induced Ca2+ entry was suppressed by more than 50%. In contrast, OAG-induced Ca2+ transients were unaffected by TRPC6 knockdown. Nevertheless, OAG-induced Ca2+ entry bore the hallmarks of TRPC6 function; it was inhibited by protein kinase C and blocked by the Src-kinase inhibitor, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine (PP2). Importantly, OAG-induced Ca2+ entry was blocked by the potent L-type Ca2+ channel inhibitor, *nimodipine. Thus, TRPC6 activation probably results primarily in Na ion entry and depolarization, leading to activation of L-type channels as the mediators of Ca2+ entry. Calculations reveal that even 90% reduction of TRPC6 channels would allow depolarization sufficient to activate L-type channels. This tight coupling between TRPC6 and L-type channels is probably important in mediating smooth muscle cell membrane potential and muscle contraction.

  • regulation of canonical transient receptor potential trpc channel function by diacylglycerol and protein kinase c
    Journal of Biological Chemistry, 2003
    Co-Authors: Kartik Venkatachalam, Fei Zheng, Donald L Gill
    Abstract:

    Abstract The mechanism of receptor-induced activation of the ubiquitously expressed family of mammalian canonical transient receptor potential (TRPC) channels has been the focus of intense study. Primarily responding to phospholipase C (PLC)-coupled receptors, the channels are reported to receive modulatory input from diacylglycerol, endoplasmic reticulum inositol 1,4,5-trisphosphate receptors and Ca2+ stores. Analysis of TRPC5 channels transfected within DT40 B cells and deletion mutants thereof revealed efficient activation in response to PLC-β or PLC-γ activation, which was independent of inositol 1,4,5-trisphoshate receptors or the content of stores. In both HEK293 cells and DT40 cells, TRPC5 and TRPC3 channel responses to PLC activation were highly analogous, but only TRPC3 and not TRPC5 channels responded to the addition of the permeant diacylglycerol (DAG) analogue, 1-oleoyl-2-acetyl-sn-glycerol (OAG). However, OAG application or elevated endogenous DAG, resulting from either DAG lipase or DAG kinase inhibition, completely prevented TRPC5 or TRPC4 activation. This inhibitory action of DAG on TRPC5 and TRPC4 channels was clearly mediated by protein kinase C (PKC), in distinction to the stimulatory action of DAG on TRPC3, which is established to be PKC-independent. PKC activation totally blocked TRPC3 channel activation in response to OAG, and the activation was restored by PKC-blockade. PKC inhibition resulted in decreased TRPC3 channel deactivation. Store-operated Ca2+ entry in response to PLC-coupled receptor activation was substantially reduced by OAG or DAG-lipase inhibition in a PKC-dependent manner. However, store-operated Ca2+ entry in response to the pump blocker, thapsigargin, was unaffected by PKC. The results reveal that each TRPC subtype is strongly inhibited by DAG-induced PKC activation, reflecting a likely universal feedback control on TRPCs, and that DAG-mediated PKC-independent activation of TRPC channels is highly subtype-specific. The profound yet distinct control by PKC and DAG of the activation of TRPC channel subtypes is likely the basis of a spectrum of regulatory phenotypes of expressed TRPC channels.

  • regulation of canonical transient receptor potential trpc channel function by diacylglycerol and protein kinase c
    Journal of Biological Chemistry, 2003
    Co-Authors: Kartik Venkatachalam, Fei Zheng, Donald L Gill
    Abstract:

    The mechanism of receptor-induced activation of the ubiquitously expressed family of mammalian canonical transient receptor potential (TRPC) channels has been the focus of intense study. Primarily responding to phospholipase C (PLC)-coupled receptors, the channels are reported to receive modulatory input from diacylglycerol, endoplasmic reticulum inositol 1,4,5-trisphosphate receptors and Ca2+ stores. Analysis of TRPC5 channels transfected within DT40 B cells and deletion mutants thereof revealed efficient activation in response to PLC-beta or PLC-gamma activation, which was independent of inositol 1,4,5-trisphoshate receptors or the content of stores. In both HEK293 cells and DT40 cells, TRPC5 and TRPC3 channel responses to PLC activation were highly analogous, but only TRPC3 and not TRPC5 channels responded to the addition of the permeant diacylglycerol (DAG) analogue, 1-oleoyl-2-acetyl-sn-glycerol (OAG). However, OAG application or elevated endogenous DAG, resulting from either DAG lipase or DAG kinase inhibition, completely prevented TRPC5 or TRPC4 activation. This inhibitory action of DAG on TRPC5 and TRPC4 channels was clearly mediated by protein kinase C (PKC), in distinction to the stimulatory action of DAG on TRPC3, which is established to be PKC-independent. PKC activation totally blocked TRPC3 channel activation in response to OAG, and the activation was restored by PKC-blockade. PKC inhibition resulted in decreased TRPC3 channel deactivation. Store-operated Ca2+ entry in response to PLC-coupled receptor activation was substantially reduced by OAG or DAG-lipase inhibition in a PKC-dependent manner. However, store-operated Ca2+ entry in response to the pump blocker, thapsigargin, was unaffected by PKC. The results reveal that each TRPC subtype is strongly inhibited by DAG-induced PKC activation, reflecting a likely universal feedback control on TRPCs, and that DAG-mediated PKC-independent activation of TRPC channels is highly subtype-specific. The profound yet distinct control by PKC and DAG of the activation of TRPC channel subtypes is likely the basis of a spectrum of regulatory phenotypes of expressed TRPC channels.

Masayuki X Mori - One of the best experts on this subject based on the ideXlab platform.

  • plc mediated pi 4 5 p2 hydrolysis regulates activation and inactivation of trpc6 7 channels
    The Journal of General Physiology, 2014
    Co-Authors: Kyohei Itsuki, Ryuji Inoue, Yuko Imai, Hideharu Hase, Yasushi Okamura, Masayuki X Mori
    Abstract:

    Transient receptor potential classical (or canonical) (TRPC)3, TRPC6, and TRPC7 are a subfamily of TRPC channels activated by diacylglycerol (DAG) produced through the hydrolysis of phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) by phospholipase C (PLC). PI(4,5)P2 depletion by a heterologously expressed phosphatase inhibits TRPC3, TRPC6, and TRPC7 activity independently of DAG; however, the physiological role of PI(4,5)P2 reduction on channel activity remains unclear. We used Forster resonance energy transfer (FRET) to measure PI(4,5)P2 or DAG dynamics concurrently with TRPC6 or TRPC7 currents after agonist stimulation of receptors that couple to Gq and thereby activate PLC. Measurements made at different levels of receptor activation revealed a correlation between the kinetics of PI(4,5)P2 reduction and those of receptor-operated TRPC6 and TRPC7 current activation and inactivation. In contrast, DAG production correlated with channel activation but not inactivation; moreover, the time course of channel inactivation was unchanged in protein kinase C–insensitive mutants. These results suggest that inactivation of receptor-operated TRPC currents is primarily mediated by the dissociation of PI(4,5)P2. We determined the functional dissociation constant of PI(4,5)P2 to TRPC channels using FRET of the PLCδ Pleckstrin homology domain (PHd), which binds PI(4,5)P2, and used this constant to fit our experimental data to a model in which channel gating is controlled by PI(4,5)P2 and DAG. This model predicted similar FRET dynamics of the PHd to measured FRET in either human embryonic kidney cells or smooth muscle cells, whereas a model lacking PI(4,5)P2 regulation failed to reproduce the experimental data, confirming the inhibitory role of PI(4,5)P2 depletion on TRPC currents. Our model also explains various PLC-dependent characteristics of channel activity, including limitation of maximum open probability, shortening of the peak time, and the bell-shaped response of total current. In conclusion, our studies demonstrate a fundamental role for PI(4,5)P2 in regulating TRPC6 and TRPC7 activity triggered by PLC-coupled receptor stimulation.