Generators of Pressure-Evoked Currents in Vertebrate Outer Retinal Neurons

(1) Background: High-tension glaucoma damages the peripheral vision dominated by rods. How mechanosensitive channels (MSCs) in the outer retina mediate pressure responses is unclear. (2) Methods: Immunocytochemistry, patch clamp, and channel fluorescence were used to study MSCs in salamander photoreceptors. (3) Results: Immunoreactivity of transient receptor potential channel vanilloid 4 (TRPV4) was revealed in the outer plexiform layer, K+ channel TRAAK in the photoreceptor outer segment (OS), and TRPV2 in some rod OS disks. Pressure on the rod inner segment evoked sustained currents of three components: A) the inward current at <−50 mV (Ipi), sensitive to Co2+; B) leak outward current at ³−80 mV (Ipo), sensitive to intracellular Cs+ and ruthenium red; and C) cation current reversed at ~10 mV (Ipc). Hypotonicity induced slow currents like Ipc. Environmental pressure and light increased the FM 1-43-identified open MSCs in the OS membrane, while pressure on the OS with internal Cs+ closed a Ca2+-dependent current reversed at ~0 mV. Rod photocurrents were thermosensitive and affected by MSC blockers. (4) Conclusions: Rods possess depolarizing (TRPV) and hyperpolarizing (K+) MSCs, which mediate mutually compensating currents between −50 mV and 10 mV, serve as an electrical cushion to minimize the impact of ocular mechanical stress.

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Regulation of calcium reabsorption along the rat nephron: a modeling study

AJP Renal Physiology ◽

10.1152/ajprenal.00577.2014 ◽

2015 ◽

Vol 308 (6) ◽

pp. F553-F566 ◽

Cited By ~ 10

Author(s):

Aurélie Edwards

Keyword(s):

Transient Receptor Potential ◽

Stone Formation ◽

Collecting Duct ◽

Receptor Potential ◽

Transient Receptor Potential Channel ◽

Transepithelial Transport ◽

Thick Ascending Limb ◽

Calcium Sensing ◽

The Impact

We expanded a mathematical model of transepithelial transport along the rat nephron to include the transport of Ca2+ and probe the impact of calcium-sensing mechanisms on Ca2+ reabsorption. The model nephron extends from the medullary thick ascending limb (mTAL) to the inner medullary collecting duct (IMCD). Our model reproduces several experimental findings, such as measurements of luminal Ca2+ concentrations in cortical tubules, and the effects of furosemide or deletion of the transient receptor potential channel vanilloid subtype 5 (TRPV5) on urinary Ca2+ excretion. In vitro microperfusion of rat TAL has demonstrated that activation of the calcium-sensing receptor CaSR lowers the TAL permeability to Ca2+, PCaTAL (Loupy A, Ramakrishnan SK, Wootla B, Chambrey R, de la Faille R, Bourgeois S, Bruneval P, Mandet C, Christensen EI, Faure H, Cheval L, Laghmani K, Collet C, Eladari D, Dodd RH, Ruat M, Houillier P. J Clin Invest 122: 3355, 2012). Our results suggest that this regulatory mechanism significantly impacts renal Ca2+ handling: when plasma Ca2+ concentration ([Ca2+]) is raised by 10%, the CaSR-mediated reduction in PCaTAL per se is predicted to enhance urinary Ca2+ excretion by ∼30%. If high [Ca2+] also induces renal outer medullary potassium (ROMK) inhibition, urinary Ca2+ excretion is further raised. In vitro, increases in luminal [Ca2+] have been shown to activate H+-ATPase pumps in the outer medullary CD and to lower the water permeability of IMCD. Our model suggests that if these responses exhibit the sigmoidal dependence on luminal [Ca2+] that is characteristic of CaSR, then the impact of elevated Ca2+ levels in the CD on urinary volume and pH remains limited. Finally, our model suggests that CaSR inhibitors could significantly reduce urinary Ca2+ excretion in hypoparathyroidism, thereby reducing the risk of calcium stone formation.

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Dissecting independent channel and scaffolding roles of the Drosophila transient receptor potential channel

The Journal of Cell Biology ◽

10.1083/jcb.200508030 ◽

2005 ◽

Vol 171 (4) ◽

pp. 685-694 ◽

Cited By ~ 28

Author(s):

Tao Wang ◽

Yuchen Jiao ◽

Craig Montell

Keyword(s):

Cell Death ◽

Retinal Degeneration ◽

Transient Receptor Potential ◽

Receptor Potential ◽

Transient Receptor Potential Channel ◽

Loss Of Function ◽

Visual Transduction ◽

Channel Function ◽

Transient Receptor ◽

The Impact

Drosophila transient receptor potential (TRP) serves dual roles as a cation channel and as a molecular anchor for the PDZ protein, INAD (inactivation no afterpotential D). Null mutations in trp cause impairment of visual transduction, mislocalization of INAD, and retinal degeneration. However, the impact of specifically altering TRP channel function is not known because existing loss-of-function alleles greatly reduce protein expression. In the current study we describe the isolation of a set of new trp alleles, including trp14 with an amino acid substitution juxtaposed to the TRP domain. The trp14 flies stably express TRP and display normal molecular anchoring, but defective channel function. Elimination of the anchoring function alone in trpΔ1272, had minor effects on retinal morphology whereas disruption of channel function caused profound light-induced cell death. This retinal degeneration was greatly suppressed by elimination of the Na+/Ca2+ exchanger, CalX, indicating that the cell death was due primarily to deficient Ca2+ entry rather than disruption of the TRP-anchoring function.

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Ca2+ Signaling and IL-8 Secretion in Human Testicular Peritubular Cells Involve the Cation Channel TRPV2

International Journal of Molecular Sciences ◽

10.3390/ijms19092829 ◽

2018 ◽

Vol 19 (9) ◽

pp. 2829 ◽

Cited By ~ 6

Author(s):

Katja Eubler ◽

Carola Herrmann ◽

Astrid Tiefenbacher ◽

Frank-Michael Köhn ◽

J. Schwarzer ◽

...

Keyword(s):

Transient Receptor Potential ◽

Receptor Potential ◽

Transient Receptor Potential Channel ◽

Ruthenium Red ◽

Cation Channel ◽

Angiogenic Factor ◽

Human Testis ◽

Seminiferous Tubules ◽

Protein Levels ◽

Peritubular Cells

Peritubular cells are part of the wall of seminiferous tubules in the human testis and their contractile abilities are important for sperm transport. In addition, they have immunological roles. A proteomic analysis of isolated human testicular peritubular cells (HTPCs) revealed expression of the transient receptor potential channel subfamily V member 2 (TRPV2). This cation channel is linked to mechano-sensation and to immunological processes and inflammation in other organs. We verified expression of TRPV2 in peritubular cells in human sections by immunohistochemistry. It was also found in other testicular cells, including Sertoli cells and interstitial cells. In cultured HTPCs, application of cannabidiol (CBD), a known TRPV2 agonist, acutely induced a transient increase in intracellular Ca2+ levels. These Ca2+ transients could be blocked both by ruthenium red, an unspecific Ca2+ channel blocker, and tranilast (TRA), an antagonist of TRPV2, and were also abolished when extracellular Ca2+ was removed. Taken together this indicates functional TRPV2 channels in peritubular cells. When applied for 24 to 48 h, CBD induced expression of proinflammatory factors. In particular, mRNA and secreted protein levels of the proinflammatory chemokine interleukin-8 (IL-8/CXCL8) were elevated. Via its known roles as a major mediator of the inflammatory response and as an angiogenic factor, this chemokine may play a role in testicular physiology and pathology.

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Increased inwardly rectifying potassium currents in HEK-293 cells expressing murine transient receptor potential 4

Biochemical Journal ◽

10.1042/bj3540717 ◽

2001 ◽

Vol 354 (3) ◽

pp. 717-725 ◽

Cited By ~ 6

Author(s):

Zongming ZHANG ◽

Yufang TANG ◽

Michael Xi ZHU

Keyword(s):

Transient Receptor Potential ◽

Outward Current ◽

Receptor Potential ◽

K Channel ◽

Hek 293 ◽

Hek 293 Cells ◽

293 Cells ◽

Transient Receptor ◽

Inwardly Rectifying ◽

K Currents

Drosophila transient receptor potential (Trp) and its mammalian homologues are postulated to form capacitative Ca2+ entry or store-operated channels. Here we show that expression of murine Trp4 in HEK 293 cells also leads to an increase in inwardly rectifying K+ currents. No similar increase was found in cell lines expressing Trp1, Trp3 or Trp6. Consistent with typical characteristics of inward rectifiers, the K+ currents in Trp4-expressing cells were blocked by low millimolar concentrations of Cs+ and Ba2+, but not by 1.2mM Ca2+, and were only slightly inhibited by 5mM tetraethylammonium. Single channel recordings of excised inside-out patches revealed the presence of two conducting states of 51pS and 94pS in Trp4-expressing cells. The outward current in the excised patches was blocked by 1mM spermine, but not by 1mM Mg2+. How Trp4 expression causes the increase in the K+ currents is not known. We propose that Trp4 either participates in the formation of a novel K+ channel or up-regulates the expression or activity of endogenous inwardly rectifying K+ channels.

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Modulating the Mechanical Activation of TRPV4 at the Cell-Substrate Interface

Frontiers in Bioengineering and Biotechnology ◽

10.3389/fbioe.2020.608951 ◽

2021 ◽

Vol 8 ◽

Author(s):

Setareh Sianati ◽

Lioba Schroeter ◽

Jessica Richardson ◽

Andy Tay ◽

Shireen R. Lamandé ◽

...

Keyword(s):

Mechanical Activation ◽

Mammalian Cells ◽

Transient Receptor Potential ◽

Point Mutations ◽

Receptor Potential ◽

Transient Receptor Potential Channel ◽

Force Sensor ◽

Substrate Interface ◽

Cell Substrate ◽

The Impact

Ion channels activated by mechanical inputs are important force sensing molecules in a wide array of mammalian cells and tissues. The transient receptor potential channel, TRPV4, is a polymodal, nonselective cation channel that can be activated by mechanical inputs but only if stimuli are applied directly at the interface between cells and their substrate, making this molecule a context-dependent force sensor. However, it remains unclear how TRPV4 is activated by mechanical inputs at the cell-substrate interface, which cell intrinsic and cell extrinsic parameters might modulate the mechanical activation of the channel and how mechanical activation differs from TRPV4 gating in response to other stimuli. Here we investigated the impact of substrate mechanics and cytoskeletal components on mechanically evoked TRPV4 currents and addressed how point mutations associated with TRPV4 phosphorylation and arthropathy influence mechanical activation of the channel. Our findings reveal distinct regulatory modulation of TRPV4 from the mechanically activated ion channel PIEZO1, suggesting the mechanosensitivity of these two channels is tuned in response to different parameters. Moreover, our data demonstrate that the effect of point mutations in TRPV4 on channel activation are profoundly dependent on the gating stimulus.

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An environmental sensor, TRPV4 is a novel regulator of intracellular Ca2+ in human synoviocytes

AJP Cell Physiology ◽

10.1152/ajpcell.00204.2009 ◽

2009 ◽

Vol 297 (5) ◽

pp. C1082-C1090 ◽

Cited By ~ 30

Author(s):

Yuka Itoh ◽

Noriyuki Hatano ◽

Hidetoshi Hayashi ◽

Kikuo Onozaki ◽

Keiji Miyazawa ◽

...

Keyword(s):

Rheumatoid Arthritis ◽

Protein Level ◽

Transient Receptor Potential ◽

Receptor Potential ◽

Transient Receptor Potential Channel ◽

Ruthenium Red ◽

Intracellular Ca ◽

Environmental Sensor ◽

Significant Expression ◽

Transient Receptor

The activation of a vanilloid type 4 transient receptor potential channel (TRPV4) has an obligatory role in regulation of intracellular Ca2+ (Ca2+i) in several types of cells including vascular and sensory organs. In this study, we provide evidence that TRPV4 is a functional regulator of Ca2+i in human synoviocytes. Although significant expression of TRPV4 in synoviocytes from patients with (RA) and without (CTR) rheumatoid arthritis was detected at mRNA and protein level, those in the human fibroblast-like synoviocyte line MH7A were rather lower. Consistently, the selective TRPV4 agonist 4α-phorbol 12,13-didecanoate (4αPDD) effectively elevated Ca2+i in the RA and CTR cells, which was abolished by the removal of external Ca2+. Moreover, the elevation was inhibited by ruthenium red, a blocker of TRPVs. In MH7A cells transfected with human TRPV4 (MH7A-V4), 4αPDD elevated the Ca2+i in a similar manner to those in the RA and CTR cells. Electrophysiological analysis also revealed that 4αPDD activated nonselective cationic currents in RA cells. Application of 227 mosM solution to the RA and MH7A-V4 cells elevated their Ca2+i, but this does not occur when it was applied to MH7A cells. Treatment of RA but not MH7A cells with 4αPDD for 24 h reduced their production of IL-8. These results suggest that an environmental sensor, TRPV4, is a novel regulator of intracellular Ca2+ in human synoviocytes.

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Transient Receptor Potential Vanilloid 5 Mediates Ca2+ Influx and Inhibits Chondrocyte Autophagy in a Rat Osteoarthritis Model

Cellular Physiology and Biochemistry ◽

10.1159/000477387 ◽

2017 ◽

Vol 42 (1) ◽

pp. 319-332 ◽

Cited By ~ 11

Author(s):

Yingliang Wei ◽

Yanfang Wang ◽

Yutong Wang ◽

Lunhao Bai

Keyword(s):

Articular Cartilage ◽

Transient Receptor Potential ◽

Joint Destruction ◽

Receptor Potential ◽

B Cell Lymphoma ◽

Transient Receptor Potential Channel ◽

Ruthenium Red ◽

Protective Mechanism ◽

Transient Receptor Potential Vanilloid ◽

Transient Receptor

Background: Autophagy, a self-protective mechanism of chondrocytes, has become a promising target to impede the progress of osteoarthritis (OA). Autophagy is regulated by cytosolic Ca2+ activity and may thus be modified by the Ca2+ permeable transient receptor potential channel vanilloid 5 (TRPV5). Therefore, we investigated the potential role of TRPV5 in mediating Ca2+ influx and in inhibiting chondrocyte autophagy in a rat OA model. Methods: The rat OA model was assessed by macroscopic and histological analyses. light chain 3B (LC3B) immunolocalization was detected by immunohistochemistry. TRPV5, LC3B and calmodulin in OA articular cartilage were assessed by real time polymerase chain reaction (RT-PCR) and western blotting. TRPV5 small interfering RNA (TRPV5 siRNA) were transfected into rat primary chondrocyte then the calmodulin and LC3B was detected by immunofluorescence. The functionality of the TRPV5 was assessed by Ca2+ influx. Western blot was used to measure autophagy-related proteins. Results: We constructed a monosodium iodoacetate (MIA) -induced rat OA model and found that ruthenium red (TRPV5 inhibitor) slowed the progression of joint destruction. We found that the TRPV5 and calmodulin were up-regulated but LC3B was down-regulated in articular cartilage following prolonged progression of OA. Furthermore, the up-regulated TRPV5 channel caused an increase in the Ca2+ influx in chondrocytes. The up-regulation of TRPV5 stimulated Ca2+ influx, which inhibited autophagy by increasing the production of calmodulin, phosphorylation of calmodulin dependent protein kinases II (p-CAMK II), phosphorylation of Beclin1 (p-Beclin1), and protein of B-cell lymphoma-2 (Bcl-2), and attenuating ratio of LC3-II/ LC3-. Conclusion: Up-regulated TRPV5 as an initiating factor inhibited chondrocyte autophagy via the mediation of Ca2+ influx.

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