1
|
Arreola J, López-Romero AE, Huerta M, Guzmán-Hernández ML, Pérez-Cornejo P. Insights into the function and regulation of the calcium-activated chloride channel TMEM16A. Cell Calcium 2024; 121:102891. [PMID: 38772195 DOI: 10.1016/j.ceca.2024.102891] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 04/23/2024] [Accepted: 04/23/2024] [Indexed: 05/23/2024]
Abstract
The TMEM16A channel, a member of the TMEM16 protein family comprising chloride (Cl-) channels and lipid scramblases, is activated by the free intracellular Ca2+ increments produced by inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release after GqPCRs or Ca2+ entry through cationic channels. It is a ubiquitous transmembrane protein that participates in multiple physiological functions essential to mammals' lives. TMEM16A structure contains two identical 10-segment monomers joined at their transmembrane segment 10. Each monomer harbours one independent hourglass-shaped pore gated by Ca2+ ligation to an orthosteric site adjacent to the pore and controlled by two gates. The orthosteric site is created by assembling negatively charged glutamate side chains near the pore´s cytosolic end. When empty, this site generates an electrostatic barrier that controls channel rectification. In addition, an isoleucine-triad forms a hydrophobic gate at the boundary of the cytosolic vestibule and the inner side of the neck. When the cytosolic Ca2+ rises, one or two Ca2+ ions bind to the orthosteric site in a voltage (V)-dependent manner, thus neutralising the electrostatic barrier and triggering an allosteric gating mechanism propagating via transmembrane segment 6 to the hydrophobic gate. These coordinated events lead to pore opening, allowing the Cl- flux to ensure the physiological response. The Ca2+-dependent function of TMEM16A is highly regulated. Anions with higher permeability than Cl- facilitate V dependence by increasing the Ca2+ sensitivity, intracellular protons can replace Ca2+ and induce channel opening, and phosphatidylinositol 4,5-bisphosphate bound to four cytosolic sites likely maintains Ca2+ sensitivity. Additional regulation is afforded by cytosolic proteins, most likely by phosphorylation and protein-protein interaction mechanisms.
Collapse
Affiliation(s)
- Jorge Arreola
- Jorge Arreola, Physics Institute of Universidad Autónoma de San Luis Potosí. Av. Parque Chapultepec 1570, Privadas del Pedregal, 78295 San Luis Potosí, SLP., Mexico.
| | - Ana Elena López-Romero
- Jorge Arreola, Physics Institute of Universidad Autónoma de San Luis Potosí. Av. Parque Chapultepec 1570, Privadas del Pedregal, 78295 San Luis Potosí, SLP., Mexico
| | - Miriam Huerta
- Jorge Arreola, Physics Institute of Universidad Autónoma de San Luis Potosí. Av. Parque Chapultepec 1570, Privadas del Pedregal, 78295 San Luis Potosí, SLP., Mexico
| | - María Luisa Guzmán-Hernández
- Catedrática CONAHCYT, Department of Physiology and Biophysics, School of Medicine, Universidad Autónoma de San Luis Potosí. Ave. V. Carranza 2905, Los Filtros, San Luis Potosí, SLP 78210, Mexico
| | - Patricia Pérez-Cornejo
- Department of Physiology and Biophysics, School of Medicine, Universidad Autónoma de San Luis Potosí. Ave. V. Carranza 2905, Los Filtros, San Luis Potosí, SLP 78210, Mexico
| |
Collapse
|
2
|
Mesnard CS, Hays CL, Barta CL, Sladek AL, Grassmeyer JJ, Hinz KK, Quadros RM, Gurumurthy CB, Thoreson WB. Synaptotagmins 1 and 7 in vesicle release from rods of mouse retina. Exp Eye Res 2022; 225:109279. [PMID: 36280223 PMCID: PMC9830644 DOI: 10.1016/j.exer.2022.109279] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Revised: 09/14/2022] [Accepted: 10/10/2022] [Indexed: 01/13/2023]
Abstract
Synaptotagmins are the primary Ca2+ sensors for synaptic exocytosis. Previous work suggested synaptotagmin-1 (Syt1) mediates evoked vesicle release from cone photoreceptor cells in the vertebrate retina whereas release from rods may involve another sensor in addition to Syt1. We found immunohistochemical evidence for syntaptotagmin-7 (Syt7) in mouse rod terminals and so performed electroretinograms (ERG) and single-cell recordings using mice in which Syt1 and/or Syt7 were conditionally removed from rods and/or cones. Synaptic release was measured in mouse rods by recording presynaptic anion currents activated during glutamate re-uptake and from exocytotic membrane capacitance changes. Deleting Syt1 from rods reduced glutamate release evoked by short depolarizing steps but not long steps whereas deleting Syt7 from rods reduced release evoked by long but not short steps. Deleting both sensors completely abolished depolarization-evoked release from rods. Effects of various intracellular Ca2+ buffers showed that Syt1-mediated release from rods involves vesicles close to ribbon-associated Ca2+ channels whereas Syt7-mediated release evoked by longer steps involves more distant release sites. Spontaneous release from rods was unaffected by eliminating Syt7. While whole animal knockout of Syt7 slightly reduced ERG b-waves and oscillatory potentials, selective elimination of Syt7 from rods had no effect on ERGs. Furthermore, eliminating Syt1 from rods and cones abolished ERG b-waves and additional elimination of Syt7 had no further effect. These results show that while Syt7 contributes to slow non-ribbon release from rods, Syt1 is the principal sensor shaping rod and cone inputs to bipolar cells in response to light flashes.
Collapse
Affiliation(s)
- C S Mesnard
- Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, USA; Pharmacology and Experimental Neuroscience, USA
| | - C L Hays
- Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, USA
| | - C L Barta
- Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, USA
| | - A L Sladek
- Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, USA
| | - J J Grassmeyer
- Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, USA; Pharmacology and Experimental Neuroscience, USA
| | - K K Hinz
- Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, USA
| | - R M Quadros
- Pharmacology and Experimental Neuroscience, USA; Mouse Genome Engineering Core Facility, Vice Chancellor for Research Office, College of Medicine, University of Nebraska Medical Center, Omaha, NE, 68106, USA
| | - C B Gurumurthy
- Pharmacology and Experimental Neuroscience, USA; Mouse Genome Engineering Core Facility, Vice Chancellor for Research Office, College of Medicine, University of Nebraska Medical Center, Omaha, NE, 68106, USA
| | - W B Thoreson
- Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, USA; Pharmacology and Experimental Neuroscience, USA.
| |
Collapse
|
3
|
Grabner CP, Moser T. The mammalian rod synaptic ribbon is essential for Ca v channel facilitation and ultrafast synaptic vesicle fusion. eLife 2021; 10:63844. [PMID: 34617508 PMCID: PMC8594941 DOI: 10.7554/elife.63844] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2020] [Accepted: 10/06/2021] [Indexed: 12/19/2022] Open
Abstract
Rod photoreceptors (PRs) use ribbon synapses to transmit visual information. To signal ‘no light detected’ they release glutamate continually to activate post-synaptic receptors. When light is detected glutamate release pauses. How a rod’s individual ribbon enables this process was studied here by recording evoked changes in whole-cell membrane capacitance from wild-type and ribbonless (Ribeye-ko) mice. Wild-type rods filled with high (10 mM) or low (0.5 mM) concentrations of the Ca2+-buffer EGTA created a readily releasable pool (RRP) of 87 synaptic vesicles (SVs) that emptied as a single kinetic phase with a τ<0.4 ms. The lower concentration of EGTA accelerated Cav channel opening and facilitated release kinetics. In contrast, ribbonless rods created a much smaller RRP of 22 SVs, and they lacked Cav channel facilitation; however, Ca2+ channel-release coupling remained tight. These release deficits caused a sharp attenuation of rod-driven scotopic light responses. We conclude that the synaptic ribbon facilitates Ca2+-influx and establishes a large RRP of SVs.
Collapse
Affiliation(s)
- Chad Paul Grabner
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany.,Collaborative Research Center 1286 'Quantitative Synaptology', University of Göttingen, Göttingen, Germany
| | - Tobias Moser
- Institute for Auditory Neuroscience and InnerEarLab, University Medical Center Göttingen, Göttingen, Germany.,Synaptic Nanophysiology Group, Max Planck Institute of Biophysical Chemistry, Göttingen, Germany.,Collaborative Research Center 1286 'Quantitative Synaptology', University of Göttingen, Göttingen, Germany.,Multiscale Bioimaging Cluster of Excellence (MBExC), University of Göttingen, Göttingen, Germany
| |
Collapse
|
4
|
Thoreson WB. Transmission at rod and cone ribbon synapses in the retina. Pflugers Arch 2021; 473:1469-1491. [PMID: 33779813 DOI: 10.1007/s00424-021-02548-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 02/23/2021] [Accepted: 02/25/2021] [Indexed: 12/29/2022]
Abstract
Light-evoked voltage responses of rod and cone photoreceptor cells in the vertebrate retina must be converted to a train of synaptic vesicle release events for transmission to downstream neurons. This review discusses the processes, proteins, and structures that shape this critical early step in vision, focusing on studies from salamander retina with comparisons to other experimental animals. Many mechanisms are conserved across species. In cones, glutamate release is confined to ribbon release sites although rods are also capable of release at non-ribbon sites. The role of non-ribbon release in rods remains unclear. Release from synaptic ribbons in rods and cones involves at least three vesicle pools: a readily releasable pool (RRP) matching the number of membrane-associated vesicles along the ribbon base, a ribbon reserve pool matching the number of additional vesicles on the ribbon, and an enormous cytoplasmic reserve. Vesicle release increases in parallel with Ca2+ channel activity. While the opening of only a few Ca2+ channels beneath each ribbon can trigger fusion of a single vesicle, sustained release rates in darkness are governed by the rate at which the RRP can be replenished. The number of vacant release sites, their functional status, and the rate of vesicle delivery in turn govern replenishment. Along with an overview of the mechanisms of exocytosis and endocytosis, we consider specific properties of ribbon-associated proteins and pose a number of remaining questions about this first synapse in the visual system.
Collapse
Affiliation(s)
- Wallace B Thoreson
- Truhlsen Eye Institute, Departments of Ophthalmology & Visual Sciences and Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA.
| |
Collapse
|
5
|
Guo J, Liu X, Zhang T, Lin X, Hong Y, Yu J, Wu Q, Zhang F, Wu Q, Shang J, Lv X, Ou J, Zhou J, Pang R, Tang B, Liang S. Hepatocyte TMEM16A Deletion Retards NAFLD Progression by Ameliorating Hepatic Glucose Metabolic Disorder. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2020; 7:1903657. [PMID: 32440483 PMCID: PMC7237841 DOI: 10.1002/advs.201903657] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Revised: 02/22/2020] [Accepted: 02/27/2020] [Indexed: 06/11/2023]
Abstract
Nonalcoholic fatty liver disease (NAFLD) is the most prevalent form of chronic liver disease, and the mechanisms underpinning its pathogenesis have not been completely established. Transmembrane member 16A (TMEM16A), a component of the Ca2+-activated chloride channel (CaCC), has recently been implicated in metabolic events. Herein, TMEM16A is shown to be responsible for CaCC activation in hepatocytes and is increased in liver tissues of mice and patients with NAFLD. Hepatocyte-specific ablation of TMEM16A in mice ameliorates high-fat diet-induced obesity, hepatic glucose metabolic disorder, steatosis, insulin resistance, and inflammation. In contrast, hepatocyte-specific TMEM16A transgenic mice exhibit the opposite phenotype. Mechanistically, hepatocyte TMEM16A interacts with vesicle-associated membrane protein 3 (VAMP3) to induce its degradation, suppressing the formation of the VAMP3/syntaxin 4 and VAMP3/synaptosome-associated protein 23 complexes. This leads to the impairment of hepatic glucose transporter 2 (GLUT2) translocation and glucose uptake. Notably, VAMP3 overexpression restrains the functions of hepatocyte TMEM16A in blocking GLUT2 translocation and promoting lipid deposition, insulin resistance, and inflammation. In contrast, VAMP3 knockdown reverses the beneficial effects of TMEM16A downregulation. This study demonstrates a role for TMEM16A in NAFLD and suggests that inhibition of hepatic TMEM16A or disruption of TMEM16A/VAMP3 interaction may provide a new potential therapeutic strategy for NAFLD.
Collapse
Affiliation(s)
- Jia‐Wei Guo
- Department of PharmacologyCardiac and Cerebral Vascular Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| | - Xiu Liu
- Department of PharmacologyCardiac and Cerebral Vascular Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| | - Ting‐Ting Zhang
- Department of PharmacologyCardiac and Cerebral Vascular Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| | - Xiao‐Chun Lin
- Department of PharmacologyCardiac and Cerebral Vascular Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| | - Yu Hong
- Department of PharmacologyCardiac and Cerebral Vascular Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| | - Jie Yu
- Department of Gastrointestinal SurgeryThe First Affiliated HospitalSun Yat‐Sen UniversityGuangzhou510080China
| | - Qin‐Yan Wu
- Department of GastroenterologyThe First People's Hospital of FoshanFoshan528000China
| | - Fei‐Ran Zhang
- Department of PharmacologyCardiac and Cerebral Vascular Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| | - Qian‐Qian Wu
- Key Laboratory of Metabolic Cardiovascular Diseases Research of National Health CommissionNingxia Medical UniversityYinchuan750004China
| | - Jin‐Yan Shang
- Department of PharmacologyCardiac and Cerebral Vascular Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| | - Xiao‐Fei Lv
- Department of PharmacologyCardiac and Cerebral Vascular Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| | - Jing‐Song Ou
- Division of Cardiac SurgeryThe Key Laboratory of Assisted CirculationMinistry of HealthThe First Affiliated HospitalSun Yat‐Sen UniversityGuangzhou510080China
- National‐Guangdong Joint Engineering Laboratory for Diagnosis and Treatment of Vascular DiseasesThe First Affiliated HospitalSun Yat‐Sen UniversityGuangzhou510080China
| | - Jia‐Guo Zhou
- Department of PharmacologyCardiac and Cerebral Vascular Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
- Program of Kidney and Cardiovascular DiseaseThe Fifth Affiliated HospitalSun Yat‐Sen UniversityGuangzhou510080China
- Department of CardiologySun Yat‐Sen Memorial HospitalSun Yat‐Sen UniversityGuangzhou510120China
- Guangdong Province Key Laboratory of Brain Function and DiseaseZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| | - Rui‐Ping Pang
- Guangdong Province Key Laboratory of Brain Function and DiseaseZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
- Department of PhysiologyPain Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| | - Bao‐Dong Tang
- Department of GastroenterologyThe First Affiliated HospitalSun Yat‐Sen UniversityGuangzhou510080China
| | - Si‐Jia Liang
- Department of PharmacologyCardiac and Cerebral Vascular Research CenterZhongshan School of MedicineSun Yat‐Sen UniversityGuangzhou510080China
| |
Collapse
|
6
|
Dembla E, Dembla M, Maxeiner S, Schmitz F. Synaptic ribbons foster active zone stability and illumination-dependent active zone enrichment of RIM2 and Cav1.4 in photoreceptor synapses. Sci Rep 2020; 10:5957. [PMID: 32249787 PMCID: PMC7136232 DOI: 10.1038/s41598-020-62734-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Accepted: 03/18/2020] [Indexed: 02/08/2023] Open
Abstract
Rod photoreceptor synapses use large, ribbon-type active zones for continuous synaptic transmission during light and dark. Since ribbons are physically connected to the active zones, we asked whether illumination-dependent changes of ribbons influence Cav1.4/RIM2 protein clusters at the active zone and whether these illumination-dependent effects at the active zone require the presence of the synaptic ribbon. We found that synaptic ribbon length and the length of presynaptic Cav1.4/RIM2 clusters are tightly correlated. Dark-adaptation did not change the number of ribbons and active zone puncta. However, mean ribbon length and length of presynaptic Cav1.4/RIM2 clusters increased significantly during dark-adaptation when tonic exocytosis is highest. In the present study, we identified by the analyses of synaptic ribbon-deficient RIBEYE knockout mice that synaptic ribbons are (1) needed to stabilize Cav1.4/RIM2 at rod photoreceptor active zones and (2) are required for the darkness-induced active zone enrichment of Cav1.4/RIM2. These data propose a role of the ribbon in active zone stabilization and suggest a homeostatic function of the ribbon in illumination-dependent active zone remodeling.
Collapse
Affiliation(s)
- Ekta Dembla
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, Saarland University, Medical School, 66421, Homburg, Germany.
| | - Mayur Dembla
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, Saarland University, Medical School, 66421, Homburg, Germany
| | - Stephan Maxeiner
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, Saarland University, Medical School, 66421, Homburg, Germany
- Institute of Anatomy and Cell Biology, Saarland University, AG Krasteva-Christ, 66421, Homburg, Germany
| | - Frank Schmitz
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, Saarland University, Medical School, 66421, Homburg, Germany.
| |
Collapse
|
7
|
Paik SS, Park YS, Kim IB. Calcium- and Voltage-Dependent Dual Gating ANO1 is an Intrinsic Determinant of Repolarization in Rod Bipolar Cells of the Mouse Retina. Cells 2020; 9:cells9030543. [PMID: 32110998 PMCID: PMC7140511 DOI: 10.3390/cells9030543] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Revised: 02/23/2020] [Accepted: 02/24/2020] [Indexed: 01/09/2023] Open
Abstract
TMEM16A/anoctamin1 (ANO1), a calcium (Ca2+)-activated chloride (Cl-) channel, has many functions in various excitable cells and modulates excitability in both Ca2+- and voltage-gating modes. However, its gating characteristics and role in primary neural cells remain unclear. Here, we characterized its Ca2+- and voltage-dependent components in rod bipolar cells using dissociated and slice preparations of the mouse retina. The I-V curves of Ca2+-dependent ANO1 tail current and voltage-gated Ca2+ channel (VGCC) are similar; as ANO1 is blocked by VGCC inhibitors, ANO1 may be gated by Ca2+ influx through VGCC. The voltage-dependent component of ANO1 has outward rectifying and sustained characteristics and is clearly isolated by the inhibitory effect of Cl- reduction and T16Ainh-A01, a selective ANO1 inhibitor, in high EGTA, a Ca2+ chelator. The voltage-dependent component disappears due to VGCC inhibition, suggesting that Ca2+ is the essential trigger for ANO1. In perforated current-clamping method, the application of T16Ainh-A01 and reduction of Cl- extended excitation periods in rod bipolar cells, revealing that ANO1 induces repolarization during excitation. Overall, ANO1 opens by VGCC activation during physiological excitation of the rod bipolar cell and has a voltage-dependent component. These two gating-modes concurrently provide the intrinsic characteristics of the membrane potential in rod bipolar cells.
Collapse
Affiliation(s)
- Sun-Sook Paik
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul 100744, Korea; (S.-S.P.); (Y.S.P.)
| | - Yong Soo Park
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul 100744, Korea; (S.-S.P.); (Y.S.P.)
| | - In-Beom Kim
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul 100744, Korea; (S.-S.P.); (Y.S.P.)
- Catholic Institute for Applied Anatomy, College of Medicine, The Catholic University of Korea, Seoul 100744, Korea
- Correspondence: ; Tel.: +82-2-2258-7263; Fax: +82-2-536-3110
| |
Collapse
|
8
|
Angiotensin-Receptor-Associated Protein Modulates Ca 2+ Signals in Photoreceptor and Mossy Fiber cells. Sci Rep 2019; 9:19622. [PMID: 31873081 PMCID: PMC6928155 DOI: 10.1038/s41598-019-55380-8] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Accepted: 11/22/2019] [Indexed: 11/29/2022] Open
Abstract
Fast, precise and sustained neurotransmission requires graded Ca2+ signals at the presynaptic terminal. Neurotransmitter release depends on a complex interplay of Ca2+ fluxes and Ca2+ buffering in the presynaptic terminal that is not fully understood. Here, we show that the angiotensin-receptor-associated protein (ATRAP) localizes to synaptic terminals throughout the central nervous system. In the retinal photoreceptor synapse and the cerebellar mossy fiber-granule cell synapse, we find that ATRAP is involved in the generation of depolarization-evoked synaptic Ca2+ transients. Compared to wild type, Ca2+ imaging in acutely isolated preparations of the retina and the cerebellum from ATRAP knockout mice reveals a significant reduction of the sarcoendoplasmic reticulum (SR) Ca2+-ATPase (SERCA) activity. Thus, in addition to its conventional role in angiotensin signaling, ATRAP also modulates presynaptic Ca2+ signaling within the central nervous system.
Collapse
|
9
|
Wen X, Thoreson WB. Contributions of glutamate transporters and Ca 2+-activated Cl - currents to feedback from horizontal cells to cone photoreceptors. Exp Eye Res 2019; 189:107847. [PMID: 31628905 DOI: 10.1016/j.exer.2019.107847] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2019] [Revised: 09/26/2019] [Accepted: 10/15/2019] [Indexed: 02/05/2023]
Abstract
Lateral inhibitory feedback from horizontal cells (HCs) to cones establishes center-surround receptive fields and color opponency in the retina. When HCs hyperpolarize to light, inhibitory feedback to cones increases activation of cone Ca2+ currents (ICa) that can in turn activate additional currents. We recorded simultaneously from cones and HCs to analyze cone currents activated by HC feedback in salamander retina. Depolarization-activated inward tail currents in cones were inhibited by CaCCinh-A01 that inhibits both Ano1 and Ano2 Ca2+-activated Cl- currents (ICl(Ca)). An Ano1-selective inhibitor Ani9 was less effective suggesting that Ano2 is the predominant ICl(Ca) subtype in cones. CaCCinh-A01 inhibited feedback currents more strongly when intracellular Ca2+ in cones was buffered with 0.05 mM EGTA compared to stronger buffering with 5 mM EGTA. By contrast, blocking glutamate transporter anion currents (ICl(Glu)) with TBOA had stronger inhibitory effects on cone feedback currents when Ca2+ buffering was strong. Inward feedback currents ran down at rates intermediate between rundown of glutamate release and ICl(Ca), consistent with contributions to feedback from both ICl(Ca) and ICl(Glu). These results suggest that Cl- channels coupled to glutamate transporters help to speed inward feedback currents initiated by local changes in intracellular [Ca2+] close to synaptic ribbons of cones whereas Ano2 Ca2+-activated Cl- channels contribute to slower components of feedback regulated by spatially extensive changes in intracellular [Ca2+].
Collapse
Affiliation(s)
- Xiangyi Wen
- Department of Ophthalmology, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China; Department of Optometry and Visual Science, West China Hospital, Sichuan University, Chengdu, Sichuan, 610041, China; Truhlsen Eye Institute, Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, USA; Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, USA
| | - Wallace B Thoreson
- Truhlsen Eye Institute, Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, USA; Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, USA.
| |
Collapse
|
10
|
Van Hook MJ, Nawy S, Thoreson WB. Voltage- and calcium-gated ion channels of neurons in the vertebrate retina. Prog Retin Eye Res 2019; 72:100760. [PMID: 31078724 PMCID: PMC6739185 DOI: 10.1016/j.preteyeres.2019.05.001] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2019] [Revised: 04/25/2019] [Accepted: 05/01/2019] [Indexed: 02/06/2023]
Abstract
In this review, we summarize studies investigating the types and distribution of voltage- and calcium-gated ion channels in the different classes of retinal neurons: rods, cones, horizontal cells, bipolar cells, amacrine cells, interplexiform cells, and ganglion cells. We discuss differences among cell subtypes within these major cell classes, as well as differences among species, and consider how different ion channels shape the responses of different neurons. For example, even though second-order bipolar and horizontal cells do not typically generate fast sodium-dependent action potentials, many of these cells nevertheless possess fast sodium currents that can enhance their kinetic response capabilities. Ca2+ channel activity can also shape response kinetics as well as regulating synaptic release. The L-type Ca2+ channel subtype, CaV1.4, expressed in photoreceptor cells exhibits specific properties matching the particular needs of these cells such as limited inactivation which allows sustained channel activity and maintained synaptic release in darkness. The particular properties of K+ and Cl- channels in different retinal neurons shape resting membrane potentials, response kinetics and spiking behavior. A remaining challenge is to characterize the specific distributions of ion channels in the more than 100 individual cell types that have been identified in the retina and to describe how these particular ion channels sculpt neuronal responses to assist in the processing of visual information by the retina.
Collapse
Affiliation(s)
- Matthew J Van Hook
- Truhlsen Eye Institute, Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, USA
| | - Scott Nawy
- Truhlsen Eye Institute, Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, USA; Department Pharmacology & Experimental Neuroscience(2), University of Nebraska Medical Center, Omaha, NE, USA
| | - Wallace B Thoreson
- Truhlsen Eye Institute, Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, USA; Department Pharmacology & Experimental Neuroscience(2), University of Nebraska Medical Center, Omaha, NE, USA.
| |
Collapse
|
11
|
Grassmeyer JJ, Cahill AL, Hays CL, Barta C, Quadros RM, Gurumurthy CB, Thoreson WB. Ca 2+ sensor synaptotagmin-1 mediates exocytosis in mammalian photoreceptors. eLife 2019; 8:e45946. [PMID: 31172949 PMCID: PMC6588344 DOI: 10.7554/elife.45946] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2019] [Accepted: 06/06/2019] [Indexed: 11/24/2022] Open
Abstract
To encode light-dependent changes in membrane potential, rod and cone photoreceptors utilize synaptic ribbons to sustain continuous exocytosis while making rapid, fine adjustments to release rate. Release kinetics are shaped by vesicle delivery down ribbons and by properties of exocytotic Ca2+ sensors. We tested the role for synaptotagmin-1 (Syt1) in photoreceptor exocytosis by using novel mouse lines in which Syt1 was conditionally removed from rods or cones. Photoreceptors lacking Syt1 exhibited marked reductions in exocytosis as measured by electroretinography and single-cell recordings. Syt1 mediated all evoked release in cones, whereas rods appeared capable of some slow Syt1-independent release. Spontaneous release frequency was unchanged in cones but increased in rods lacking Syt1. Loss of Syt1 did not alter synaptic anatomy or reduce Ca2+ currents. These results suggest that Syt1 mediates both phasic and tonic release at photoreceptor synapses, revealing unexpected flexibility in the ability of Syt1 to regulate Ca2+-dependent synaptic transmission.
Collapse
Affiliation(s)
- Justin J Grassmeyer
- Truhlsen Eye Institute, Department of Ophthalmology and Visual SciencesUniversity of Nebraska Medical CenterOmahaUnited States
- Department of Pharmacology and Experimental NeuroscienceUniversity of Nebraska Medical CenterOmahaUnited States
| | - Asia L Cahill
- Truhlsen Eye Institute, Department of Ophthalmology and Visual SciencesUniversity of Nebraska Medical CenterOmahaUnited States
| | - Cassandra L Hays
- Truhlsen Eye Institute, Department of Ophthalmology and Visual SciencesUniversity of Nebraska Medical CenterOmahaUnited States
- Department of Cellular and Integrative PhysiologyUniversity of Nebraska Medical CenterOmahaUnited States
| | - Cody Barta
- Truhlsen Eye Institute, Department of Ophthalmology and Visual SciencesUniversity of Nebraska Medical CenterOmahaUnited States
| | - Rolen M Quadros
- Mouse Genome Engineering Core Facility, Vice Chancellor for Research OfficeUniversity of Nebraska Medical CenterOmahaUnited States
| | - Channabasavaiah B Gurumurthy
- Mouse Genome Engineering Core Facility, Vice Chancellor for Research OfficeUniversity of Nebraska Medical CenterOmahaUnited States
- Developmental Neuroscience, Munroe Meyer Institute for Genetics and RehabilitationUniversity of Nebraska Medical CenterOmahaUnited States
| | - Wallace B Thoreson
- Truhlsen Eye Institute, Department of Ophthalmology and Visual SciencesUniversity of Nebraska Medical CenterOmahaUnited States
- Department of Pharmacology and Experimental NeuroscienceUniversity of Nebraska Medical CenterOmahaUnited States
| |
Collapse
|
12
|
Grove JCR, Hirano AA, de los Santos J, McHugh CF, Purohit S, Field GD, Brecha NC, Barnes S. Novel hybrid action of GABA mediates inhibitory feedback in the mammalian retina. PLoS Biol 2019; 17:e3000200. [PMID: 30933967 PMCID: PMC6459543 DOI: 10.1371/journal.pbio.3000200] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2018] [Revised: 04/11/2019] [Accepted: 03/13/2019] [Indexed: 01/06/2023] Open
Abstract
The stream of visual information sent from photoreceptors to second-order bipolar cells is intercepted by laterally interacting horizontal cells that generate feedback to optimize and improve the efficiency of signal transmission. The mechanisms underlying the regulation of graded photoreceptor synaptic output in this nonspiking network have remained elusive. Here, we analyze with patch clamp recording the novel mechanisms by which horizontal cells control pH in the synaptic cleft to modulate photoreceptor neurotransmitter release. First, we show that mammalian horizontal cells respond to their own GABA release and that the results of this autaptic action affect cone voltage-gated Ca2+ channel (CaV channel) gating through changes in pH. As a proof-of-principle, we demonstrate that chemogenetic manipulation of horizontal cells with exogenous anion channel expression mimics GABA-mediated cone CaV channel inhibition. Activation of these GABA receptor anion channels can depolarize horizontal cells and increase cleft acidity via Na+/H+ exchanger (NHE) proton extrusion, which results in inhibition of cone CaV channels. This action is effectively counteracted when horizontal cells are sufficiently hyperpolarized by increased GABA receptor (GABAR)-mediated HCO3- efflux, alkalinizing the cleft and disinhibiting cone CaV channels. This demonstrates how hybrid actions of GABA operate in parallel to effect voltage-dependent pH changes, a novel mechanism for regulating synaptic output.
Collapse
Affiliation(s)
- James C. R. Grove
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Neuroscience Graduate Program, University of California, San Francisco, California, United States of America
| | - Arlene A. Hirano
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, California, United States of America
| | - Janira de los Santos
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Cyrus F. McHugh
- Doheny Eye Institute, University of California, Los Angeles, California, United States of America
| | - Shashvat Purohit
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Greg D. Field
- Department of Neurobiology, Duke University School of Medicine, Durham, North Carolina, United States of America
| | - Nicholas C. Brecha
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, California, United States of America
- Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Stein Eye Institute, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
| | - Steven Barnes
- Department of Neurobiology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Doheny Eye Institute, University of California, Los Angeles, California, United States of America
- Department of Ophthalmology, David Geffen School of Medicine, University of California, Los Angeles, California, United States of America
- Department of Physiology and Biophysics, Dalhousie University, Halifax, Nova Scotia, Canada
- Department of Ophthalmology and Visual Sciences, Dalhousie University, Halifax, Nova Scotia, Canada
| |
Collapse
|
13
|
Mazzone A, Gibbons SJ, Eisenman ST, Strege PR, Zheng T, D'Amato M, Ordog T, Fernandez-Zapico ME, Farrugia G. Direct repression of anoctamin 1 ( ANO1) gene transcription by Gli proteins. FASEB J 2019; 33:6632-6642. [PMID: 30802137 DOI: 10.1096/fj.201802373r] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The Ca2+-activated Cl- channel, anoctamin 1 (Ano1, also known as transmembrane protein 16A) contributes to intestinal pacemaking, fluid secretion, cellular excitability, and tissue development. The human ANO1 promoter contains binding sites for the glioma-associated oncogene (Gli) proteins. We investigated regulation of ANO1 transcription by Gli. ANO1 promoter activity was determined using a luciferase reporter system. Binding and functional effects of Glis on ANO1 transcription and expression were demonstrated by chromatin immunoprecipitation, small interfering RNA knockdown, PCR, immunolabeling, and recordings of Ca2+-activated Cl- currents in human embryonic kidney 293 (HEK293) cells. Results from previous genome-wide association studies were used to test ANO1 promoter polymorphisms for association with disease. Gli1 and Gli2 bound to the promoter and repressed ANO1 transcription. Repression depended on Gli binding to a site close to the ANO1 transcriptional start site. Mutation of this site prevented Gli binding and transcriptional repression. Knockdown of Gli expression and inhibition of Gli activity increased expression of ANO1 RNA and Ca2+-activated Cl- currents in HEK293 cells. A single-nucleotide polymorphism prevented Gli binding and showed association with irritable bowel syndrome. We conclude that Gli1 and Gli2 repress ANO1 by a novel mechanism that is independent of Gli cleavage and that has a role in gastrointestinal function.-Mazzone, A., Gibbons, S. J., Eisenman, S. T., Strege, P. R., Zheng, T., D'Amato, M., Ordog, T., Fernandez-Zapico, M. E., Farrugia, G. Direct repression of anoctamin 1 (ANO1) gene transcription by Gli proteins.
Collapse
Affiliation(s)
- Amelia Mazzone
- Enteric NeuroSciences, Mayo Clinic, Rochester, Minnesota, USA
| | - Simon J Gibbons
- Enteric NeuroSciences, Mayo Clinic, Rochester, Minnesota, USA
| | - Seth T Eisenman
- Enteric NeuroSciences, Mayo Clinic, Rochester, Minnesota, USA
| | - Peter R Strege
- Enteric NeuroSciences, Mayo Clinic, Rochester, Minnesota, USA
| | - Tenghao Zheng
- Department of Medicine Solna and Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden
| | - Mauro D'Amato
- Department of Medicine Solna and Center for Molecular Medicine, Karolinska Institutet, Stockholm, Sweden.,Biodonostia Health Research Institute, San Sebastián, Spain.,Ikerbasque-Basque Science Foundation, San Sebastián, Spain
| | - Tamas Ordog
- Enteric NeuroSciences, Mayo Clinic, Rochester, Minnesota, USA
| | | | | |
Collapse
|
14
|
Modes of Accessing Bicarbonate for the Regulation of Membrane Guanylate Cyclase (ROS-GC) in Retinal Rods and Cones. eNeuro 2019; 6:eN-NWR-0393-18. [PMID: 30783616 PMCID: PMC6378327 DOI: 10.1523/eneuro.0393-18.2019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Revised: 12/20/2018] [Accepted: 01/15/2019] [Indexed: 11/21/2022] Open
Abstract
The membrane guanylate cyclase, ROS-GC, that synthesizes cyclic GMP for use as a second messenger for visual transduction in retinal rods and cones, is stimulated by bicarbonate. Bicarbonate acts directly on ROS-GC1, because it enhanced the enzymatic activity of a purified, recombinant fragment of bovine ROS-GC1 consisting solely of the core catalytic domain. Moreover, recombinant ROS-GC1 proved to be a true sensor of bicarbonate, rather than a sensor for CO2. Access to bicarbonate differed in rods and cones of larval salamander, Ambystoma tigrinum, of unknown sex. In rods, bicarbonate entered at the synapse and diffused to the outer segment, where it was removed by Cl--dependent exchange. In contrast, cones generated bicarbonate internally from endogenous CO2 or from exogenous CO2 that was present in extracellular solutions of bicarbonate. Bicarbonate production from both sources of CO2 was blocked by the carbonic anhydrase inhibitor, acetazolamide. Carbonic anhydrase II expression was verified immunohistochemically in cones but not in rods. In addition, cones acquired bicarbonate at their outer segments as well as at their inner segments. The multiple pathways for access in cones may support greater uptake of bicarbonate than in rods and buffer changes in its intracellular concentration.
Collapse
|
15
|
Seo KH, Jin Y, Jung SY, Lee SH. Comprehensive behavioral analyses of anoctamin1/TMEM16A-conditional knockout mice. Life Sci 2018; 207:323-331. [PMID: 29928889 DOI: 10.1016/j.lfs.2018.06.019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2018] [Revised: 06/07/2018] [Accepted: 06/15/2018] [Indexed: 10/28/2022]
Abstract
AIMS Anoctamin-1 (TMEM16A) is a calcium-activated chloride channel that is involved in numerous physiological conditions. Its role has been identified in electrophysiological and histological studies of genetic knockout animals. Recent cellular localization studies have shown that anoctamin-1 is co-expressed with presynaptic proteins, therefore its role in presynaptic terminals has been suggested. However, behavioral studies are lacking because conventional knockouts of anoctamin-1 are lethal after birth. In this study, we explored the role of anoctamin-1 in presynaptic terminals by analyzing the behavior of mice with conditional knockouts of anoctamin-1 in synapsin1-expressing cells. MAIN METHODS Using a synapsin1-Cre system, we selectively ablated anoctamin-1 in synapsin1 expressing cells. The mice were used in the behavioral experiments when they were between 6 and 9 months of age. KEY FINDINGS The mice with the conditional knockout of anoctamin-1 in synapsin1-expressing cells displayed impaired social behavior. In addition, the mice showed depressive-like behavior and decreased weight. However, these animals displayed normal locomotor activity, cognitive function, and motor coordination. SIGNIFICANCE These results suggested that anoctamin-1 is involved in psychiatric behavior because of its role in the regulation of synaptic transmission in presynaptic terminals.
Collapse
Affiliation(s)
- Kyoung Hee Seo
- Department of Pharmacology, College of Pharmacy, Chung-Ang University, Seoul 06974, Republic of Korea
| | - Yeonsun Jin
- Department of Pharmacology, College of Pharmacy, Chung-Ang University, Seoul 06974, Republic of Korea
| | - Sun-Young Jung
- College of Pharmacy, Chung-Ang University, Seoul, Republic of Korea
| | - Sung Hoon Lee
- Department of Pharmacology, College of Pharmacy, Chung-Ang University, Seoul 06974, Republic of Korea.
| |
Collapse
|
16
|
Zhang Y, Zhang Z, Xiao S, Tien J, Le S, Le T, Jan LY, Yang H. Inferior Olivary TMEM16B Mediates Cerebellar Motor Learning. Neuron 2017; 95:1103-1111.e4. [PMID: 28858616 DOI: 10.1016/j.neuron.2017.08.010] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2017] [Revised: 07/17/2017] [Accepted: 08/04/2017] [Indexed: 01/31/2023]
Abstract
Ca2+-activated ion channels shape membrane excitability and Ca2+ dynamics in response to cytoplasmic Ca2+ elevation. Compared to the Ca2+-activated K+ channels, known as BK and SK channels, the physiological importance of Ca2+-activated Cl- channels (CaCCs) in neurons has been largely overlooked. Here we report that CaCCs coexist with BK and SK channels in inferior olivary (IO) neurons that send climbing fibers to innervate cerebellar Purkinje cells for the control of motor learning and timing. Ca2+ influx through the dendritic high-threshold voltage-gated Ca2+ channels activates CaCCs, which contribute to membrane repolarization of IO neurons. Loss of TMEM16B expression resulted in the absence of CaCCs in IO neurons, leading to markedly diminished action potential firing of IO neurons in TMEM16B knockout mice. Moreover, these mutant mice exhibited severe cerebellar motor learning deficits. Our findings thus advance the understanding of the neurophysiology of CaCCs and the ionic basis of IO neuron excitability.
Collapse
Affiliation(s)
- Yang Zhang
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
| | - Zhushan Zhang
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
| | - Shaohua Xiao
- Departments of Physiology, Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Jason Tien
- Departments of Physiology, Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Son Le
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
| | - Trieu Le
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
| | - Lily Y Jan
- Departments of Physiology, Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94158, USA.
| | - Huanghe Yang
- Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA; Department of Neurobiology, Duke University Medical Center, Durham, NC 27710, USA.
| |
Collapse
|
17
|
Wang H, Zou L, Ma K, Yu J, Wu H, Wei M, Xiao Q. Cell-specific mechanisms of TMEM16A Ca 2+-activated chloride channel in cancer. Mol Cancer 2017; 16:152. [PMID: 28893247 PMCID: PMC5594453 DOI: 10.1186/s12943-017-0720-x] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2017] [Accepted: 09/01/2017] [Indexed: 02/08/2023] Open
Abstract
TMEM16A (known as anoctamin 1) Ca2+-activated chloride channel is overexpressed in many tumors. TMEM16A overexpression can be caused by gene amplification in many tumors harboring 11q13 amplification. TMEM16A expression is also controlled in many cancer cells via transcriptional regulation, epigenetic regulation and microRNAs. In addition, TMEM16A activates different signaling pathways in different cancers, e.g. the EGFR and CAMKII signaling in breast cancer, the p38 and ERK1/2 signaling in hepatoma, the Ras-Raf-MEK-ERK1/2 signaling in head and neck squamous cell carcinoma and bladder cancer, and the NFκB signaling in glioma. Furthermore, TMEM16A overexpression has been reported to promote, inhibit, or produce no effects on cell proliferation and migration in different cancer cells. Since TMEM16A exerts different roles in different cancer cells via activation of distinct signaling pathways, we try to develop the idea that TMEM16A regulates cancer cell proliferation and migration in a cell-dependent mechanism. The cell-specific role of TMEM16A may depend on the cellular environment that is predetermined by TMEM16A overexpression mechanisms specific for a particular cancer type. TMEM16A may exert its cell-specific role via its associated protein networks, phosphorylation by different kinases, and involvement of different signaling pathways. In addition, we discuss the role of TMEM16A channel activity in cancer, and its clinical use as a prognostic and predictive marker in different cancers. This review highlights the cell-type specific mechanisms of TMEM16A in cancer, and envisions the promising use of TMEM16A inhibitors as a potential treatment for TMEM16A-overexpressing cancers.
Collapse
Affiliation(s)
- Hui Wang
- Department of Ion Channel Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang, 110122 China
| | - Liang Zou
- Department of Anesthesiology, National Cancer Center/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100021 China
| | - Ke Ma
- Department of Ion Channel Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang, 110122 China
| | - Jiankun Yu
- Department of Ion Channel Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang, 110122 China
| | - Huizhe Wu
- Department of Pharmacology, School of Pharmacy, China Medical University, Shenyang, 110122 China
| | - Minjie Wei
- Department of Pharmacology, School of Pharmacy, China Medical University, Shenyang, 110122 China
| | - Qinghuan Xiao
- Department of Ion Channel Pharmacology, School of Pharmacy, China Medical University, No.77 Puhe Road, Shenyang North New Area, Shenyang, 110122 China
| |
Collapse
|
18
|
Grassmeyer JJ, Thoreson WB. Synaptic Ribbon Active Zones in Cone Photoreceptors Operate Independently from One Another. Front Cell Neurosci 2017; 11:198. [PMID: 28744203 PMCID: PMC5504102 DOI: 10.3389/fncel.2017.00198] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2017] [Accepted: 06/26/2017] [Indexed: 12/04/2022] Open
Abstract
Cone photoreceptors depolarize in darkness to release glutamate-laden synaptic vesicles. Essential to release is the synaptic ribbon, a structure that helps organize active zones by clustering vesicles near proteins that mediate exocytosis, including voltage-gated Ca2+ channels. Cone terminals have many ribbon-style active zones at which second-order neurons receive input. We asked whether there are functionally significant differences in local Ca2+ influx among ribbons in individual cones. We combined confocal Ca2+ imaging to measure Ca2+ influx at individual ribbons and patch clamp recordings to record whole-cell ICa in salamander cones. We found that the voltage for half-maximal activation (V50) of whole cell ICa in cones averaged −38.1 mV ± 3.05 mV (standard deviation [SD]), close to the cone membrane potential in darkness of ca. −40 mV. Ca2+ signals at individual ribbons varied in amplitude from one another and showed greater variability in V50 values than whole-cell ICa, suggesting that Ca2+ signals can differ significantly among ribbons within cones. After accounting for potential sources of technical variability in measurements of Ca2+ signals and for contributions from cone-to-cone differences in ICa, we found that the variability in V50 values for ribbon Ca2+ signals within individual cones showed a SD of 2.5 mV. Simulating local differences in Ca2+ channel activity at two ribbons by shifting the V50 value of ICa by ±2.5 mV (1 SD) about the mean suggests that when the membrane depolarizes to −40 mV, two ribbons could experience differences in Ca2+ influx of >45%. Further evidence that local Ca2+ changes at ribbons can be regulated independently was obtained in experiments showing that activation of inhibitory feedback from horizontal cells (HCs) to cones in paired recordings changed both amplitude and V50 of Ca2+ signals at individual ribbons. By varying the strength of synaptic output, differences in voltage dependence and amplitude of Ca2+ signals at individual ribbons shape the information transmitted from cones to downstream neurons in vision.
Collapse
Affiliation(s)
- Justin J Grassmeyer
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical CenterOmaha, NE, United States.,Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, University of Nebraska Medical CenterOmaha, NE, United States
| | - Wallace B Thoreson
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical CenterOmaha, NE, United States.,Truhlsen Eye Institute and Department of Ophthalmology and Visual Sciences, University of Nebraska Medical CenterOmaha, NE, United States
| |
Collapse
|
19
|
Chapot CA, Euler T, Schubert T. How do horizontal cells 'talk' to cone photoreceptors? Different levels of complexity at the cone-horizontal cell synapse. J Physiol 2017; 595:5495-5506. [PMID: 28378516 DOI: 10.1113/jp274177] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 03/27/2017] [Indexed: 11/08/2022] Open
Abstract
The first synapse of the retina plays a fundamental role in the visual system. Due to its importance, it is critical that it encodes information from the outside world with the greatest accuracy and precision possible. Cone photoreceptor axon terminals contain many individual synaptic sites, each represented by a presynaptic structure called a 'ribbon'. These synapses are both highly sophisticated and conserved. Each ribbon relays the light signal to one ON cone bipolar cell and several OFF cone bipolar cells, while two dendritic processes from a GABAergic interneuron, the horizontal cell, modulate the cone output via parallel feedback mechanisms. The presence of these three partners within a single synapse has raised numerous questions, and its anatomical and functional complexity is still only partially understood. However, the understanding of this synapse has recently evolved, as a consequence of progress in understanding dendritic signal processing and its role in facilitating global versus local signalling. Indeed, for the downstream retinal network, dendritic processing in horizontal cells may be essential, as they must support important functional operations such as contrast enhancement, which requires spatial averaging of the photoreceptor array, while at the same time preserving accurate spatial information. Here, we review recent progress made towards a better understanding of the cone synapse, with an emphasis on horizontal cell function, and discuss why such complexity might be necessary for early visual processing.
Collapse
Affiliation(s)
- Camille A Chapot
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany.,Centre for Integrative Neuroscience, University of Tübingen, 72076, Tübingen, Germany.,Graduate Training Centre of Neuroscience, University of Tübingen, 72076, Tübingen, Germany
| | - Thomas Euler
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany.,Centre for Integrative Neuroscience, University of Tübingen, 72076, Tübingen, Germany.,Bernstein Centre for Computational Neuroscience, University of Tübingen, 72076, Tübingen, Germany
| | - Timm Schubert
- Institute for Ophthalmic Research, University of Tübingen, 72076, Tübingen, Germany.,Centre for Integrative Neuroscience, University of Tübingen, 72076, Tübingen, Germany
| |
Collapse
|
20
|
A Presynaptic Group III mGluR Recruits Gβγ/SNARE Interactions to Inhibit Synaptic Transmission by Cone Photoreceptors in the Vertebrate Retina. J Neurosci 2017; 37:4618-4634. [PMID: 28363980 DOI: 10.1523/jneurosci.2948-16.2017] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Revised: 03/27/2017] [Accepted: 03/28/2017] [Indexed: 11/21/2022] Open
Abstract
G-protein βγ subunits (Gβγ) interact with presynaptic proteins and regulate neurotransmitter release downstream of Ca2+ influx. To accomplish their roles in sensory signaling, photoreceptor synapses use specialized presynaptic proteins that support neurotransmission at active zone structures known as ribbons. While several G-protein coupled receptors (GPCRs) influence synaptic transmission at ribbon synapses of cones and other retinal neurons, it is unknown whether Gβγ contributes to these effects. We tested whether activation of one particular GPCR, a metabotropic glutamate receptor (mGluR), can reduce cone synaptic transmission via Gβγ in tiger salamander retinas. In recordings from horizontal cells, we found that an mGluR agonist (L-AP4) reduced cone-driven light responses and mEPSC frequency. In paired recordings of cones and horizontal cells, L-AP4 slightly reduced cone ICa (∼10%) and caused a larger reduction in cone-driven EPSCs (∼30%). Proximity ligation assay revealed direct interactions between SNAP-25 and Gβγ subunits in retinal synaptic layers. Pretreatment with the SNAP-25 cleaving protease BoNT/A inhibited L-AP4 effects on synaptic transmission, as did introduction of a peptide derived from the SNAP-25 C terminus. Introducing Gβγ subunits directly into cones reduced EPSC amplitude. This effect was inhibited by BoNT/A, supporting a role for Gβγ/SNAP-25 interactions. However, the mGluR-dependent reduction in ICa was not mimicked by Gβγ, indicating that this effect was independent of Gβγ. The finding that synaptic transmission at cone ribbon synapses is regulated by Gβγ/SNAP-25 interactions indicates that these mechanisms are shared by conventional and ribbon-type synapses. Gβγ liberated from other photoreceptor GPCRs is also likely to regulate synaptic transmission.SIGNIFICANCE STATEMENT Dynamic regulation of synaptic transmission by presynaptic G-protein coupled receptors shapes information flow through neural circuits. At the first synapse in the visual system, presynaptic metabotropic glutamate receptors (mGluRs) regulate cone photoreceptor synaptic transmission, although the mechanisms and functional impact of this are unclear. We show that mGluRs regulate light response encoding across the cone synapse, accomplished in part by triggering G-protein βγ subunits (Gβγ) interactions with SNAP-25, a core component of the synaptic vesicle fusion machinery. In addition to revealing a role in visual processing, this provides the first demonstration that Gβγ/SNAP-25 interactions regulate synaptic function at a ribbon-type synapse, contributing to an emerging picture of the ubiquity of Gβγ/SNARE interactions in regulating synaptic transmission throughout the nervous system.
Collapse
|
21
|
Warren TJ, Van Hook MJ, Supuran CT, Thoreson WB. Sources of protons and a role for bicarbonate in inhibitory feedback from horizontal cells to cones in Ambystoma tigrinum retina. J Physiol 2016; 594:6661-6677. [PMID: 27345444 DOI: 10.1113/jp272533] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2016] [Accepted: 06/16/2016] [Indexed: 12/13/2022] Open
Abstract
KEY POINTS In the vertebrate retina, photoreceptors influence the signalling of neighbouring photoreceptors through lateral-inhibitory interactions mediated by horizontal cells (HCs). These interactions create antagonistic centre-surround receptive fields important for detecting edges and generating chromatically opponent responses in colour vision. The mechanisms responsible for inhibitory feedback from HCs involve changes in synaptic cleft pH that modulate photoreceptor calcium currents. However, the sources of synaptic protons involved in feedback and the mechanisms for their removal from the cleft when HCs hyperpolarize to light remain unknown. Our results indicate that Na+ -H+ exchangers are the principal source of synaptic cleft protons involved in HC feedback but that synaptic cleft alkalization during light-evoked hyperpolarization of HCs also involves changes in bicarbonate transport across the HC membrane. In addition to delineating processes that establish lateral inhibition in the retina, these results contribute to other evidence showing the key role for pH in regulating synaptic signalling throughout the nervous system. ABSTRACT Lateral-inhibitory feedback from horizontal cells (HCs) to photoreceptors involves changes in synaptic cleft pH accompanying light-evoked changes in HC membrane potential. We analysed HC to cone feedback by studying surround-evoked light responses of cones and by obtaining paired whole cell recordings from cones and HCs in salamander retina. We tested three potential sources for synaptic cleft protons: (1) generation by extracellular carbonic anhydrase (CA), (2) release from acidic synaptic vesicles and (3) Na+ /H+ exchangers (NHEs). Neither antagonizing extracellular CA nor blocking loading of protons into synaptic vesicles eliminated feedback. However, feedback was eliminated when extracellular Na+ was replaced with choline and significantly reduced by an NHE inhibitor, cariporide. Depriving NHEs of intracellular protons by buffering HC cytosol with a pH 9.2 pipette solution eliminated feedback, whereas alkalinizing the cone cytosol did not, suggesting that HCs are a major source for protons in feedback. We also examined mechanisms for changing synaptic cleft pH in response to changes in HC membrane potential. Increasing the trans-membrane proton gradient by lowering the extracellular pH from 7.8 to 7.4 to 7.1 strengthened feedback. While maintaining constant extracellular pH with 1 mm HEPES, removal of bicarbonate abolished feedback. Elevating intracellular bicarbonate levels within HCs prevented this loss of feedback. A bicarbonate transport inhibitor, 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS), also blocked feedback. Together, these results suggest that NHEs are the primary source of extracellular protons in HC feedback but that changes in cleft pH accompanying changes in HC membrane voltage also require bicarbonate flux across the HC membrane.
Collapse
Affiliation(s)
- Ted J Warren
- Department of Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA.,Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Matthew J Van Hook
- Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| | - Claudiu T Supuran
- University of Florence, Neurofarba Department, Sesto Fiorentino, Italy
| | - Wallace B Thoreson
- Department of Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, 68198, USA.,Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE, 68198, USA
| |
Collapse
|
22
|
Cork KM, Van Hook MJ, Thoreson WB. Mechanisms, pools, and sites of spontaneous vesicle release at synapses of rod and cone photoreceptors. Eur J Neurosci 2016; 44:2015-27. [PMID: 27255664 DOI: 10.1111/ejn.13288] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2016] [Revised: 05/21/2016] [Accepted: 05/24/2016] [Indexed: 01/31/2023]
Abstract
Photoreceptors have depolarized resting potentials that stimulate calcium-dependent release continuously from a large vesicle pool but neurons can also release vesicles without stimulation. We characterized the Ca(2+) dependence, vesicle pools, and release sites involved in spontaneous release at photoreceptor ribbon synapses. In whole-cell recordings from light-adapted horizontal cells (HCs) of tiger salamander retina, we detected miniature excitatory post-synaptic currents (mEPSCs) when no stimulation was applied to promote exocytosis. Blocking Ca(2+) influx by lowering extracellular Ca(2+) , by application of Cd(2+) and other agents reduced the frequency of mEPSCs but did not eliminate them, indicating that mEPSCs can occur independently of Ca(2+) . We also measured release presynaptically from rods and cones by examining quantal glutamate transporter anion currents. Presynaptic quantal event frequency was reduced by Cd(2+) or by increased intracellular Ca(2+) buffering in rods, but not in cones, that were voltage clamped at -70 mV. By inhibiting the vesicle cycle with bafilomycin, we found the frequency of mEPSCs declined more rapidly than the amplitude of evoked excitatory post-synaptic currents (EPSCs) suggesting a possible separation between vesicle pools in evoked and spontaneous exocytosis. We mapped sites of Ca(2+) -independent release using total internal reflectance fluorescence (TIRF) microscopy to visualize fusion of individual vesicles loaded with dextran-conjugated pHrodo. Spontaneous release in rods occurred more frequently at non-ribbon sites than evoked release events. The function of Ca(2+) -independent spontaneous release at continuously active photoreceptor synapses remains unclear, but the low frequency of spontaneous quanta limits their impact on noise.
Collapse
Affiliation(s)
- Karlene M Cork
- Truhlsen Eye Institute, Department of Ophthalmology & Visual Sciences, 4050 Durham Research Center, University of Nebraska Medical Center, Omaha, NE, 68198-5840, USA.,Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, USA
| | - Matthew J Van Hook
- Truhlsen Eye Institute, Department of Ophthalmology & Visual Sciences, 4050 Durham Research Center, University of Nebraska Medical Center, Omaha, NE, 68198-5840, USA
| | - Wallace B Thoreson
- Truhlsen Eye Institute, Department of Ophthalmology & Visual Sciences, 4050 Durham Research Center, University of Nebraska Medical Center, Omaha, NE, 68198-5840, USA.,Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, USA
| |
Collapse
|
23
|
Zhang W, Schmelzeisen S, Parthier D, Frings S, Möhrlen F. Anoctamin Calcium-Activated Chloride Channels May Modulate Inhibitory Transmission in the Cerebellar Cortex. PLoS One 2015; 10:e0142160. [PMID: 26558388 PMCID: PMC4641602 DOI: 10.1371/journal.pone.0142160] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 10/19/2015] [Indexed: 01/18/2023] Open
Abstract
Calcium-activated chloride channels of the anoctamin (alias TMEM16) protein family fulfill critical functions in epithelial fluid transport, smooth muscle contraction and sensory signal processing. Little is known, however, about their contribution to information processing in the central nervous system. Here we examined the recent finding that a calcium-dependent chloride conductance impacts on GABAergic synaptic inhibition in Purkinje cells of the cerebellum. We asked whether anoctamin channels may underlie this chloride conductance. We identified two anoctamin channel proteins, ANO1 and ANO2, in the cerebellar cortex. ANO1 was expressed in inhibitory interneurons of the molecular layer and the granule cell layer. Both channels were expressed in Purkinje cells but, while ANO1 appeared to be retained in the cell body, ANO2 was targeted to the dendritic tree. Functional studies confirmed that ANO2 was involved in a calcium-dependent mode of ionic plasticity that reduces the efficacy of GABAergic synapses. ANO2 channels attenuated GABAergic transmission by increasing the postsynaptic chloride concentration, hence reducing the driving force for chloride influx. Our data suggest that ANO2 channels are involved in a Ca2+-dependent regulation of synaptic weight in GABAergic inhibition. Thus, in balance with the chloride extrusion mechanism via the co-transporter KCC2, ANO2 appears to regulate ionic plasticity in the cerebellum.
Collapse
Affiliation(s)
- Weiping Zhang
- Department of Animal Molecular Physiology, Centre of Organismal Studies, Im Neuenheimer Feld 504, Heidelberg University, Heidelberg, Germany
| | - Steffen Schmelzeisen
- Department of Animal Molecular Physiology, Centre of Organismal Studies, Im Neuenheimer Feld 504, Heidelberg University, Heidelberg, Germany
| | - Daniel Parthier
- Department of Animal Molecular Physiology, Centre of Organismal Studies, Im Neuenheimer Feld 504, Heidelberg University, Heidelberg, Germany
| | - Stephan Frings
- Department of Animal Molecular Physiology, Centre of Organismal Studies, Im Neuenheimer Feld 504, Heidelberg University, Heidelberg, Germany
| | - Frank Möhrlen
- Department of Animal Molecular Physiology, Centre of Organismal Studies, Im Neuenheimer Feld 504, Heidelberg University, Heidelberg, Germany
- * E-mail:
| |
Collapse
|
24
|
Thoreson WB, Van Hook MJ, Parmelee C, Curto C. Modeling and measurement of vesicle pools at the cone ribbon synapse: Changes in release probability are solely responsible for voltage-dependent changes in release. Synapse 2015; 70:1-14. [PMID: 26541100 DOI: 10.1002/syn.21871] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Revised: 09/21/2015] [Accepted: 10/06/2015] [Indexed: 12/16/2022]
Abstract
Postsynaptic responses are a product of quantal amplitude (Q), size of the releasable vesicle pool (N), and release probability (P). Voltage-dependent changes in presynaptic Ca(2+) entry alter postsynaptic responses primarily by changing P but have also been shown to influence N. With simultaneous whole cell recordings from cone photoreceptors and horizontal cells in tiger salamander retinal slices, we measured N and P at cone ribbon synapses by using a train of depolarizing pulses to stimulate release and deplete the pool. We developed an analytical model that calculates the total pool size contributing to release under different stimulus conditions by taking into account the prior history of release and empirically determined properties of replenishment. The model provided a formula that calculates vesicle pool size from measurements of the initial postsynaptic response and limiting rate of release evoked by a train of pulses, the fraction of release sites available for replenishment, and the time constant for replenishment. Results of the model showed that weak and strong depolarizing stimuli evoked release with differing probabilities but the same size vesicle pool. Enhancing intraterminal Ca(2+) spread by lowering Ca(2+) buffering or applying BayK8644 did not increase PSCs evoked with strong test steps, showing there is a fixed upper limit to pool size. Together, these results suggest that light-evoked changes in cone membrane potential alter synaptic release solely by changing release probability.
Collapse
Affiliation(s)
- Wallace B Thoreson
- Truhlsen Eye Institute, Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska.,Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska
| | - Matthew J Van Hook
- Truhlsen Eye Institute, Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska
| | - Caitlyn Parmelee
- Department of Mathematics, University of Nebraska, Lincoln, Nebraska
| | - Carina Curto
- Department of Mathematics, University of Nebraska, Lincoln, Nebraska.,Department of Mathematics, Pennsylvania State University, State College, Pennsylvania
| |
Collapse
|
25
|
Caputo A, Piano I, Demontis GC, Bacchi N, Casarosa S, Della Santina L, Gargini C. TMEM16A is associated with voltage-gated calcium channels in mouse retina and its function is disrupted upon mutation of the auxiliary α2δ4 subunit. Front Cell Neurosci 2015; 9:422. [PMID: 26557056 PMCID: PMC4617175 DOI: 10.3389/fncel.2015.00422] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 10/04/2015] [Indexed: 02/02/2023] Open
Abstract
Photoreceptors rely upon highly specialized synapses to efficiently transmit signals to multiple postsynaptic targets. Calcium influx in the presynaptic terminal is mediated by voltage-gated calcium channels (VGCC). This event triggers neurotransmitter release, but also gates calcium-activated chloride channels (TMEM), which in turn regulate VGCC activity. In order to investigate the relationship between VGCC and TMEM channels, we analyzed the retina of wild type (WT) and Cacna2d4 mutant mice, in which the VGCC auxiliary α2δ4 subunit carries a nonsense mutation, disrupting the normal channel function. Synaptic terminals of mutant photoreceptors are disarranged and synaptic proteins as well as TMEM16A channels lose their characteristic localization. In parallel, calcium-activated chloride currents are impaired in rods, despite unaltered TMEM16A protein levels. Co-immunoprecipitation revealed the interaction between VGCC and TMEM16A channels in the retina. Heterologous expression of these channels in tsA-201 cells showed that TMEM16A associates with the CaV1.4 subunit, and the association persists upon expression of the mutant α2δ4 subunit. Collectively, our experiments show association between TMEM16A and the α1 subunit of VGCC. Close proximity of these channels allows optimal function of the photoreceptor synaptic terminal under physiological conditions, but also makes TMEM16A channels susceptible to changes occurring to calcium channels.
Collapse
Affiliation(s)
| | - Ilaria Piano
- Department of Pharmacy, University of Pisa Pisa, Italy
| | | | - Niccolò Bacchi
- Centre for Integrative Biology, University of Trento Trento, Italy
| | - Simona Casarosa
- Centre for Integrative Biology, University of Trento Trento, Italy
| | | | | |
Collapse
|
26
|
Van Hook MJ, Thoreson WB. Weak endogenous Ca2+ buffering supports sustained synaptic transmission by distinct mechanisms in rod and cone photoreceptors in salamander retina. Physiol Rep 2015; 3:3/9/e12567. [PMID: 26416977 PMCID: PMC4600400 DOI: 10.14814/phy2.12567] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Differences in synaptic transmission between rod and cone photoreceptors contribute to different response kinetics in rod- versus cone-dominated visual pathways. We examined Ca2+ dynamics in synaptic terminals of tiger salamander photoreceptors under conditions that mimicked endogenous buffering to determine the influence on kinetically and mechanistically distinct components of synaptic transmission. Measurements of ICl(Ca) confirmed that endogenous Ca2+ buffering is equivalent to ˜0.05 mmol/L EGTA in rod and cone terminals. Confocal imaging showed that with such buffering, depolarization stimulated large, spatially unconstrained [Ca2+] increases that spread throughout photoreceptor terminals. We calculated immediately releasable pool (IRP) size and release efficiency in rods by deconvolving excitatory postsynaptic currents and presynaptic Ca2+ currents. Peak efficiency of ˜0.2 vesicles/channel was similar to that of cones (˜0.3 vesicles/channel). Efficiency in both cell types was not significantly affected by using weak endogenous Ca2+ buffering. However, weak Ca2+ buffering speeded Ca2+/calmodulin (CaM)-dependent replenishment of vesicles to ribbons in both rods and cones, thereby enhancing sustained release. In rods, weak Ca2+ buffering also amplified sustained release by enhancing CICR and CICR-stimulated release of vesicles at nonribbon sites. By contrast, elevating [Ca2+] at nonribbon sites in cones with weak Ca2+ buffering and by inhibiting Ca2+ extrusion did not trigger additional release, consistent with the notion that exocytosis from cones occurs exclusively at ribbons. The presence of weak endogenous Ca2+ buffering in rods and cones facilitates slow, sustained exocytosis by enhancing Ca2+/CaM-dependent replenishment of ribbons in both rods and cones and by stimulating nonribbon release triggered by CICR in rods.
Collapse
Affiliation(s)
- Matthew J Van Hook
- Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska
| | - Wallace B Thoreson
- Truhlsen Eye Institute and Department of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska Department of Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska
| |
Collapse
|
27
|
Maurya DK, Henriques T, Marini M, Pedemonte N, Galietta LJV, Rock JR, Harfe BD, Menini A. Development of the Olfactory Epithelium and Nasal Glands in TMEM16A-/- and TMEM16A+/+ Mice. PLoS One 2015; 10:e0129171. [PMID: 26067252 PMCID: PMC4465891 DOI: 10.1371/journal.pone.0129171] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Accepted: 05/05/2015] [Indexed: 12/16/2022] Open
Abstract
TMEM16A/ANO1 is a calcium-activated chloride channel expressed in several types of epithelia and involved in various physiological processes, including proliferation and development. During mouse embryonic development, the expression of TMEM16A in the olfactory epithelium is dynamic. TMEM16A is expressed at the apical surface of the entire olfactory epithelium at embryonic day E12.5 while from E16.5 its expression is restricted to a region near the transition zone with the respiratory epithelium. To investigate whether TMEM16A plays a role in the development of the mouse olfactory epithelium, we obtained the first immunohistochemistry study comparing the morphological properties of the olfactory epithelium and nasal glands in TMEM16A-/- and TMEM16A+/+ littermate mice. A comparison between the expression of the olfactory marker protein and adenylyl cyclase III shows that genetic ablation of TMEM16A did not seem to affect the maturation of olfactory sensory neurons and their ciliary layer. As TMEM16A is expressed at the apical part of supporting cells and in their microvilli, we used ezrin and cytokeratin 8 as markers of microvilli and cell body of supporting cells, respectively, and found that morphology and development of supporting cells were similar in TMEM16A-/- and TMEM16A+/+ littermate mice. The average number of supporting cells, olfactory sensory neurons, horizontal and globose basal cells were not significantly different in the two types of mice. Moreover, we also observed that the morphology of Bowman’s glands, nasal septal glands and lateral nasal glands did not change in the absence of TMEM16A. Our results indicate that the development of mouse olfactory epithelium and nasal glands does not seem to be affected by the genetic ablation of TMEM16A.
Collapse
Affiliation(s)
- Devendra Kumar Maurya
- Laboratory of Olfactory Transduction, SISSA, International School for Advanced Studies, Trieste, Italy
| | - Tiago Henriques
- Laboratory of Olfactory Transduction, SISSA, International School for Advanced Studies, Trieste, Italy
| | | | | | | | - Jason R. Rock
- Department of Anatomy, UCSF School of Medicine, San Francisco, CA, United States of America
| | - Brian D. Harfe
- Department of Molecular Genetics and Microbiology Genetics Institute, University of Florida, College of Medicine, Gainesville, FL, United States of America
| | - Anna Menini
- Laboratory of Olfactory Transduction, SISSA, International School for Advanced Studies, Trieste, Italy
- * E-mail:
| |
Collapse
|
28
|
Mazzone A, Gibbons SJ, Bernard CE, Nowsheen S, Middha S, Almada LL, Ordog T, Kendrick ML, Reid Lombardo KM, Shen KR, Galietta LJV, Fernandez-Zapico ME, Farrugia G. Identification and characterization of a novel promoter for the human ANO1 gene regulated by the transcription factor signal transducer and activator of transcription 6 (STAT6). FASEB J 2014; 29:152-63. [PMID: 25351986 DOI: 10.1096/fj.14-258541] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Anoctamin-1 (Ano1) is a widely expressed protein responsible for endogenous Ca(2+)-activated Cl(-) currents. Ano1 is overexpressed in cancer. Differential expression of transcriptional variants is also found in other diseases. However, the mechanisms underlying regulation of Ano1 are unknown. This study identifies the Ano1 promoter and defines a mechanism for regulating its expression. Next-generation RNA sequencing (RNA-seq) analysis in human gastric muscle found a new exon upstream of the reported exon 1 and identified a promoter proximal to this new exon. Reporter assays in human embryonic kidney 293 cells showed a 6.7 ± 2.1-fold increase in activity over empty vector. Treatment with a known regulator of Ano1 expression, IL-4, increased promoter activity by 1.6 ± 0.02-fold over untreated cells. The promoter region contained putative binding sites for multiple transcription factors including signal transducer and activator of transcription 6 (STAT6), a downstream effector of IL-4. Chromatin immunoprecipitation (ChIP) experiments on T84 cells, which endogenously express Ano1, showed a 2.1 ± 0.12-fold increase in binding of STAT6 to P0 after IL-4 treatment. These results were confirmed by mutagenesis, expression, and RNA interference techniques. This work allows deeper understanding of the regulation of Ano1 in physiology and as a potential therapeutic target in a variety of diseases.
Collapse
Affiliation(s)
| | | | | | | | | | - Luciana L Almada
- Schulze Center for Novel Therapeutics, Department of Oncology, and
| | | | | | | | - K Robert Shen
- Department of Surgery, Mayo Clinic, Rochester, Minnesota, USA; and
| | | | | | | |
Collapse
|
29
|
Van Hook MJ, Thoreson WB. Endogenous calcium buffering at photoreceptor synaptic terminals in salamander retina. Synapse 2014; 68:518-28. [PMID: 25049035 DOI: 10.1002/syn.21768] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2014] [Revised: 06/09/2014] [Accepted: 07/02/2014] [Indexed: 11/12/2022]
Abstract
Calcium operates by several mechanisms to regulate glutamate release at rod and cone synaptic terminals. In addition to serving as the exocytotic trigger, Ca2+ accelerates replenishment of vesicles in cones and triggers Ca2+-induced Ca2+ release (CICR) in rods. Ca2+ thereby amplifies sustained exocytosis, enabling photoreceptor synapses to encode constant and changing light. A complete picture of the role of Ca2+ in regulating synaptic transmission requires an understanding of the endogenous Ca2+ handling mechanisms at the synapse. We therefore used the "added buffer" approach to measure the endogenous Ca2+ binding ratio (κendo ) and extrusion rate constant (γ) in synaptic terminals of photoreceptors in retinal slices from tiger salamander. We found that κendo was similar in both cell types-∼25 and 50 in rods and cones, respectively. Using measurements of the decay time constants of Ca2+ transients, we found that γ was also similar, with values of ∼100 s(-1) and 160 s(-1) in rods and cones, respectively. The measurements of κendo differ considerably from measurements in retinal bipolar cells, another ribbon-bearing class of retinal neurons, but are comparable to similar measurements at other conventional synapses. The values of γ are slower than at other synapses, suggesting that Ca2+ ions linger longer in photoreceptor terminals, supporting sustained exocytosis, CICR, and Ca2+ -dependent ribbon replenishment. The mechanisms of endogenous Ca2+ handling in photoreceptors are thus well-suited for supporting tonic neurotransmission. Similarities between rod and cone Ca2+ handling suggest that neither buffering nor extrusion underlie differences in synaptic transmission kinetics.
Collapse
Affiliation(s)
- Matthew J Van Hook
- Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska, 68198
| | | |
Collapse
|
30
|
Vocke K, Dauner K, Hahn A, Ulbrich A, Broecker J, Keller S, Frings S, Möhrlen F. Calmodulin-dependent activation and inactivation of anoctamin calcium-gated chloride channels. ACTA ACUST UNITED AC 2014; 142:381-404. [PMID: 24081981 PMCID: PMC3787769 DOI: 10.1085/jgp.201311015] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Calcium-dependent chloride channels serve critical functions in diverse biological systems. Driven by cellular calcium signals, the channels codetermine excitatory processes and promote solute transport. The anoctamin (ANO) family of membrane proteins encodes three calcium-activated chloride channels, named ANO 1 (also TMEM16A), ANO 2 (also TMEM16B), and ANO 6 (also TMEM16F). Here we examined how ANO 1 and ANO 2 interact with Ca2+/calmodulin using nonstationary current analysis during channel activation. We identified a putative calmodulin-binding domain in the N-terminal region of the channel proteins that is involved in channel activation. Binding studies with peptides indicated that this domain, a regulatory calmodulin-binding motif (RCBM), provides two distinct modes of interaction with Ca2+/calmodulin, one at submicromolar Ca2+ concentrations and one in the micromolar Ca2+ range. Functional, structural, and pharmacological data support the concept that calmodulin serves as a calcium sensor that is stably associated with the RCBM domain and regulates the activation of ANO 1 and ANO 2 channels. Moreover, the predominant splice variant of ANO 2 in the brain exhibits Ca2+/calmodulin-dependent inactivation, a loss of channel activity within 30 s. This property may curtail ANO 2 activity during persistent Ca2+ signals in neurons. Mutagenesis data indicated that the RCBM domain is also involved in ANO 2 inactivation, and that inactivation is suppressed in the retinal ANO 2 splice variant. These results advance the understanding of Ca2+ regulation in anoctamin Cl− channels and its significance for the physiological function that anoctamin channels subserve in neurons and other cell types.
Collapse
Affiliation(s)
- Kerstin Vocke
- Department of Molecular Physiology, Centre for Organismal Studies, Heidelberg University, 69120 Heidelberg, Germany
| | | | | | | | | | | | | | | |
Collapse
|
31
|
Abstract
TMEM16 proteins, also known as anoctamins, are involved in a variety of functions that include ion transport, phospholipid scrambling, and regulation of other membrane proteins. The first two members of the family, TMEM16A (anoctamin-1, ANO1) and TMEM16B (anoctamin-2, ANO2), function as Ca2+-activated Cl- channels (CaCCs), a type of ion channel that plays important functions such as transepithelial ion transport, smooth muscle contraction, olfaction, phototransduction, nociception, and control of neuronal excitability. Genetic ablation of TMEM16A in mice causes impairment of epithelial Cl- secretion, tracheal abnormalities, and block of gastrointestinal peristalsis. TMEM16A is directly regulated by cytosolic Ca2+ as well as indirectly by its interaction with calmodulin. Other members of the anoctamin family, such as TMEM16C, TMEM16D, TMEM16F, TMEM16G, and TMEM16J, may work as phospholipid scramblases and/or ion channels. In particular, TMEM16F (ANO6) is a major contributor to the process of phosphatidylserine translocation from the inner to the outer leaflet of the plasma membrane. Intriguingly, TMEM16F is also associated with the appearance of anion/cation channels activated by very high Ca2+ concentrations. Furthermore, a TMEM16 protein expressed in Aspergillus fumigatus displays both ion channel and lipid scramblase activity. This finding suggests that dual function is an ancestral characteristic of TMEM16 proteins and that some members, such as TMEM16A and TMEM16B, have evolved to a pure channel function. Mutations in anoctamin genes (ANO3, ANO5, ANO6, and ANO10) cause various genetic diseases. These diseases suggest the involvement of anoctamins in a variety of cell functions whose link with ion transport and/or lipid scrambling needs to be clarified.
Collapse
|
32
|
Schmitz F. Presynaptic [Ca(2+)] and GCAPs: aspects on the structure and function of photoreceptor ribbon synapses. Front Mol Neurosci 2014; 7:3. [PMID: 24567702 PMCID: PMC3915146 DOI: 10.3389/fnmol.2014.00003] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Accepted: 01/15/2014] [Indexed: 12/21/2022] Open
Abstract
Changes in intracellular calcium ions [Ca2+] play important roles in photoreceptor signaling. Consequently, intracellular [Ca2+] levels need to be tightly controlled. In the light-sensitive outer segments (OS) of photoreceptors, Ca2+ regulates the activity of retinal guanylate cyclases thus playing a central role in phototransduction and light-adaptation by restoring light-induced decreases in cGMP. In the synaptic terminals, changes of intracellular Ca2+ trigger various aspects of neurotransmission. Photoreceptors employ tonically active ribbon synapses that encode light-induced, graded changes of membrane potential into modulation of continuous synaptic vesicle exocytosis. The active zones of ribbon synapses contain large electron-dense structures, synaptic ribbons, that are associated with large numbers of synaptic vesicles. Synaptic coding at ribbon synapses differs from synaptic coding at conventional (phasic) synapses. Recent studies revealed new insights how synaptic ribbons are involved in this process. This review focuses on the regulation of [Ca2+] in presynaptic photoreceptor terminals and on the function of a particular Ca2+-regulated protein, the neuronal calcium sensor protein GCAP2 (guanylate cyclase-activating protein-2) in the photoreceptor ribbon synapse. GCAP2, an EF-hand-containing protein plays multiple roles in the OS and in the photoreceptor synapse. In the OS, GCAP2 works as a Ca2+-sensor within a Ca2+-regulated feedback loop that adjusts cGMP levels. In the photoreceptor synapse, GCAP2 binds to RIBEYE, a component of synaptic ribbons, and mediates Ca2+-dependent plasticity at that site. Possible mechanisms are discussed.
Collapse
Affiliation(s)
- Frank Schmitz
- Department of Neuroanatomy, Institute for Anatomy and Cell Biology, Medical School Homburg/Saar, Saarland University Saarland, Germany
| |
Collapse
|
33
|
Jeon JH, Paik SS, Chun MH, Oh U, Kim IB. Presynaptic Localization and Possible Function of Calcium-Activated Chloride Channel Anoctamin 1 in the Mammalian Retina. PLoS One 2013; 8:e67989. [PMID: 23840801 PMCID: PMC3693959 DOI: 10.1371/journal.pone.0067989] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2013] [Accepted: 05/23/2013] [Indexed: 11/18/2022] Open
Abstract
Calcium (Ca(2+))-activated chloride (Cl(-)) channels (CaCCs) play a role in the modulation of action potentials and synaptic responses in the somatodendritic regions of central neurons. In the vertebrate retina, large Ca(2+)-activated Cl(-) currents (ICl(Ca)) regulate synaptic transmission at photoreceptor terminals; however, the molecular identity of CaCCs that mediate ICl(Ca) remains unclear. The transmembrane protein, TMEM16A, also called anoctamin 1 (ANO1), has been recently validated as a CaCC and is widely expressed in various secretory epithelia and nervous tissues. Despite the fact that tmem16a was first cloned in the retina, there is little information on its cellular localization and function in the mammalian retina. In this study, we found that ANO1 was abundantly expressed as puncta in 2 synaptic layers. More specifically, ANO1 immunoreactivity was observed in the presynaptic terminals of various retinal neurons, including photoreceptors. ICl(Ca) was first detected in dissociated rod bipolar cells expressing ANO1. ICl(Ca) was abolished by treatment with the Ca(2+) channel blocker Co(2+), the L-type Ca(2+) channel blocker nifedipine, and the Cl(-) channel blockers 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB) and niflumic acid (NFA). More specifically, a recently discovered ANO1-selective inhibitor, T16Ainh-A01, and a neutralizing antibody against ANO1 inhibited ICl(Ca) in rod bipolar cells. Under a current-clamping mode, the suppression of ICl(Ca) by using NPPB and T16Ainh-A01 caused a prolonged Ca(2+) spike-like depolarization evoked by current injection in dissociated rod bipolar cells. These results suggest that ANO1 confers ICl(Ca) in retinal neurons and acts as an intrinsic regulator of the presynaptic membrane potential during synaptic transmission.
Collapse
Affiliation(s)
- Ji Hyun Jeon
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul, Korea
- Catholic Neuroscience Institute, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Sun Sook Paik
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul, Korea
- Catholic Neuroscience Institute, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Myung-Hoon Chun
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul, Korea
| | - Uhtaek Oh
- Channel Research Center, College of Pharmacy, Seoul National University, Seoul, Korea
| | - In-Beom Kim
- Department of Anatomy, College of Medicine, The Catholic University of Korea, Seoul, Korea
- Catholic Neuroscience Institute, College of Medicine, The Catholic University of Korea, Seoul, Korea
- Catholic Institute for Applied Anatomy, College of Medicine, The Catholic University of Korea, Seoul, Korea
- * E-mail:
| |
Collapse
|
34
|
Properties of ribbon and non-ribbon release from rod photoreceptors revealed by visualizing individual synaptic vesicles. J Neurosci 2013; 33:2071-86. [PMID: 23365244 DOI: 10.1523/jneurosci.3426-12.2013] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Vesicle release from rod photoreceptors is regulated by Ca(2+) entry through L-type channels located near synaptic ribbons. We characterized sites and kinetics of vesicle release in salamander rods by using total internal reflection fluorescence microscopy to visualize fusion of individual synaptic vesicles. A small number of vesicles were loaded by brief incubation with FM1-43 or a dextran-conjugated, pH-sensitive form of rhodamine, pHrodo. Labeled organelles matched the diffraction-limited size of fluorescent microspheres and disappeared rapidly during stimulation. Consistent with fusion, depolarization-evoked vesicle disappearance paralleled electrophysiological release kinetics and was blocked by inhibiting Ca(2+) influx. Rods maintained tonic release at resting membrane potentials near those in darkness, causing depletion of membrane-associated vesicles unless Ca(2+) entry was inhibited. This depletion of release sites implies that sustained release may be rate limited by vesicle delivery. During depolarizing stimulation, newly appearing vesicles approached the membrane at ∼800 nm/s, where they paused for ∼60 ms before fusion. With fusion, vesicles advanced ∼18 nm closer to the membrane. Release events were concentrated near ribbons, but lengthy depolarization also triggered release from more distant non-ribbon sites. Consistent with greater contributions from non-ribbon sites during lengthier depolarization, damaging the ribbon by fluorophore-assisted laser inactivation (FALI) of Ribeye caused only weak inhibition of exocytotic capacitance increases evoked by 200-ms depolarizing test steps, whereas FALI more strongly inhibited capacitance increases evoked by 25 ms steps. Amplifying release by use of non-ribbon sites when rods are depolarized in darkness may improve detection of decrements in release when they hyperpolarize to light.
Collapse
|
35
|
Abstract
Following synaptic vesicle exocytosis, neurons retrieve the fused membrane by a process of endocytosis to provide a supply of vesicles for subsequent release and maintain the presynaptic active zone. Rod and cone photoreceptors use a specialized structure called the synaptic ribbon that enables them to sustain high rates of neurotransmitter release. They must also employ mechanisms of synaptic vesicle endocytosis capable of keeping up with release. While much is known about endocytosis at another retinal ribbon synapse, that of the goldfish Mb1 bipolar cell, less is known about endocytosis in photoreceptors. We used capacitance recording techniques to measure vesicle membrane fusion and retrieval in photoreceptors from salamander retinal slices. We found that application of brief depolarizing steps (<100 ms) to cones evoked exocytosis followed by rapid endocytosis with a time constant ∼250 ms. In some cases, the capacitance trace overshot the baseline, indicating excess endocytosis. Calcium had no effect on the time constant, but enhanced excess endocytosis resulting in a faster rate of membrane retrieval. Surprisingly, endocytosis was unaffected by blockers of dynamin, suggesting that cone endocytosis is dynamin independent. This contrasts with synaptic vesicle endocytosis in rods, which was inhibited by the dynamin inhibitor dynasore and GTPγS introduced through the patch pipette, suggesting that the two photoreceptor types employ distinct pathways for vesicle retrieval. The fast kinetics of synaptic vesicle endocytosis in photoreceptors likely enables these cells to maintain a high rate of transmitter release, allowing them to faithfully signal changes in illumination to second-order neurons.
Collapse
|
36
|
Thoreson WB, Mercer AJ, Cork KM, Szalewski RJ. Lateral mobility of L-type calcium channels in synaptic terminals of retinal bipolar cells. Mol Vis 2013; 19:16-24. [PMID: 23335847 PMCID: PMC3548577] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2012] [Accepted: 01/02/2013] [Indexed: 11/30/2022] Open
Abstract
PURPOSE Efficient and precise release of glutamate from retinal bipolar cells is ensured by the positioning of L-type Ca(2+) channels close to release sites at the base of the synaptic ribbon. We investigated whether Ca(2+) channels at bipolar cell ribbon synapses are fixed in position or capable of moving in the membrane. METHODS We tracked the movements of individual L-type Ca(2+) channels in bipolar cell terminals after labeling channels with quantum dots (QDs) attached to α(2)δ(4) accessory Ca(2+) channel subunits via intermediary antibodies. RESULTS We found that individual Ca(2+) channels moved within a confined domain of 0.13-0.15 μm(2) in bipolar cell terminals, similar to ultrastructural estimates of the surface area of the active zone beneath the ribbon. Disruption of actin expanded the confinement domain indicating that cytoskeletal interactions help to confine channels at the synapse, but the relatively large diffusion coefficients of 0.3-0.45 μm(2)/s suggest that channels are not directly anchored to actin. Unlike photoreceptor synapses, removing membrane cholesterol did not change domain size, indicating that lipid rafts are not required to confine Ca(2+) channels at bipolar cell ribbon synapses. CONCLUSIONS The ability of Ca(2+) channels to move within the presynaptic active zone suggests that regulating channel mobility may affect release from bipolar cell terminals.
Collapse
Affiliation(s)
- Wallace B. Thoreson
- Departments of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE,Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE
| | - Aaron J. Mercer
- Department of Molecular & Integrative Physiology, University of Michigan, Ann Arbor, MI
| | - Karlene M. Cork
- Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE
| | - Robert J. Szalewski
- Departments of Ophthalmology & Visual Sciences, University of Nebraska Medical Center, Omaha, NE
| |
Collapse
|
37
|
Mercer AJ, Thoreson WB. Tracking quantum dot-tagged calcium channels at vertebrate photoreceptor synapses: retinal slices and dissociated cells. CURRENT PROTOCOLS IN NEUROSCIENCE 2013; Chapter 2:Unit 2.18. [PMID: 23315944 PMCID: PMC3707139 DOI: 10.1002/0471142301.ns0218s62] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
At synapses in the central nervous system, precisely localized assemblies of presynaptic proteins, neurotransmitter-filled vesicles, and postsynaptic receptors are required to communicate messages between neurons. Our understanding of synaptic function has been significantly advanced using electrophysiological methods, but the dynamic spatial behavior and real-time organization of synapses remains poorly understood. In this unit, we describe a method for labeling individual presynaptic calcium channels with photostable quantum dots for single-particle tracking analysis. We have used this technique to examine the mobility of L-type calcium channels in the presynaptic membrane of rod and cone photoreceptors in the retina. These channels control release of glutamate-filled synaptic vesicles at the ribbon synapses in photoreceptor terminals. This technique offers the advantage of providing a real-time biophysical readout of ion channel mobility and can be manipulated by pharmacological or electrophysiological methods. For example, the combination of electrophysiological and single-particle tracking experiments has revealed that fusion of nearby vesicles influences calcium channel mobility and changes in channel mobility can influence release. These approaches can also be readily adapted to examine membrane proteins in other systems.
Collapse
Affiliation(s)
- Aaron J Mercer
- Departments of Molecular and Integrative Physiology, University Of Michigan, Ann Arbor, USA
| | | |
Collapse
|
38
|
Abstract
Photoreceptors are exquisitely adapted to transform light stimuli into electrical signals that modulate neurotransmitter release. These cells are organized into several compartments including the unique outer segment (OS). Its whole function is to absorb light and transduce this signal into a change of membrane potential. Another compartment is the inner segment where much of metabolism and regulation of membrane potential takes place and that connects the OS and synapse. The synapse is the compartment where changes in membrane potentials are relayed to other neurons in the retina via release of neurotransmitter. The composition of the plasma membrane surrounding these compartments varies to accommodate their specific functions. In this chapter, we discuss the organization of the plasma membrane emphasizing the protein composition of each region as it relates to visual signaling. We also point out examples where mutations in these proteins cause visual impairment.
Collapse
Affiliation(s)
- Sheila A Baker
- Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, Iowa, USA.
| | | |
Collapse
|
39
|
|
40
|
Endeman D, Fahrenfort I, Sjoerdsma T, Steijaert M, Ten Eikelder H, Kamermans M. Chloride currents in cones modify feedback from horizontal cells to cones in goldfish retina. J Physiol 2012; 590:5581-95. [PMID: 22890705 DOI: 10.1113/jphysiol.2012.240325] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
In neuronal systems, excitation and inhibition must be well balanced to ensure reliable information transfer. The cone/horizontal cell (HC) interaction in the retina is an example of this. Because natural scenes encompass an enormous intensity range both in temporal and spatial domains, the balance between excitation and inhibition in the outer retina needs to be adaptable. How this is achieved is unknown. Using electrophysiological techniques in the isolated retina of the goldfish, it was found that opening Ca(2+)-dependent Cl(-) channels in recorded cones reduced the size of feedback responses measured in both cones and HCs. Furthermore, we show that cones express Cl(-) channels that are gated by GABA released from HCs. Similar to activation of I(Cl(Ca)), opening of these GABA-gated Cl(-) channels reduced the size of light-induced feedback responses both in cones and HCs. Conversely, application of picrotoxin, a blocker of GABA(A) and GABA(C) receptors, had the opposite effect. In addition, reducing GABA release from HCs by blocking GABA transporters also led to an increase in the size of feedback. Because the independent manipulation of Ca(2+)-dependent Cl(-) currents in individual cones yielded results comparable to bath-applied GABA, it was concluded that activation of either Cl(-) current by itself is sufficient to reduce the size of HC feedback. However, additional effects of GABA on outer retinal processing cannot be excluded. These results can be accounted for by an ephaptic feedback model in which a cone Cl(-) current shunts the current flow in the synaptic cleft. The Ca(2+)-dependent Cl(-) current might be essential to set the initial balance between the feedforward and the feedback signals active in the cone HC synapse. It prevents that strong feedback from HCs to cones flood the cone with Ca(2)(+). Modulation of the feedback strength by GABA might play a role during light/dark adaptation, adjusting the amount of negative feedback to the signal to noise ratio of the cone output.
Collapse
Affiliation(s)
- Duco Endeman
- The Netherlands Institute for Neuroscience, Retinal Signal Processing, Meibergdreef 47, 1105 BA Amsterdam, The Netherlands
| | | | | | | | | | | |
Collapse
|
41
|
The dynamic architecture of photoreceptor ribbon synapses: cytoskeletal, extracellular matrix, and intramembrane proteins. Vis Neurosci 2012; 28:453-71. [PMID: 22192503 DOI: 10.1017/s0952523811000356] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Rod and cone photoreceptors possess ribbon synapses that assist in the transmission of graded light responses to second-order bipolar and horizontal cells of the vertebrate retina. Proper functioning of the synapse requires the juxtaposition of presynaptic release sites immediately adjacent to postsynaptic receptors. In this review, we focus on the synaptic, cytoskeletal, and extracellular matrix proteins that help to organize photoreceptor ribbon synapses in the outer plexiform layer. We examine the proteins that foster the clustering of release proteins, calcium channels, and synaptic vesicles in the presynaptic terminals of photoreceptors adjacent to their postsynaptic contacts. Although many proteins interact with one another in the presynaptic terminal and synaptic cleft, these protein-protein interactions do not create a static and immutable structure. Instead, photoreceptor ribbon synapses are remarkably dynamic, exhibiting structural changes on both rapid and slow time scales.
Collapse
|
42
|
Mercer AJ, Szalewski RJ, Jackman SL, Van Hook MJ, Thoreson WB. Regulation of presynaptic strength by controlling Ca2+ channel mobility: effects of cholesterol depletion on release at the cone ribbon synapse. J Neurophysiol 2012; 107:3468-78. [PMID: 22442573 DOI: 10.1152/jn.00779.2011] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Synaptic communication requires proper coupling between voltage-gated Ca(2+) (Ca(V)) channels and synaptic vesicles. In photoreceptors, L-type Ca(V) channels are clustered close to synaptic ribbon release sites. Although clustered, Ca(V) channels move continuously within a confined domain slightly larger than the base of the ribbon. We hypothesized that expanding Ca(V) channel confinement domains should increase the number of channel openings needed to trigger vesicle release. Using single-particle tracking techniques, we measured the expansion of Ca(V) channel confinement domains caused by depletion of membrane cholesterol with cholesterol oxidase or methyl-β-cyclodextrin. With paired whole cell recordings from cones and horizontal cells, we then determined the number of Ca(V) channel openings contributing to cone Ca(V) currents (I(Ca)) and the number of vesicle fusion events contributing to horizontal cell excitatory postsynaptic currents (EPSCs) following cholesterol depletion. Expansion of Ca(V) channel confinement domains reduced the peak efficiency of release, decreasing the number of vesicle fusion events accompanying opening of each Ca(V) channel. Cholesterol depletion also inhibited exocytotic capacitance increases evoked by brief depolarizing steps. Changes in efficiency were not due to changes in I(Ca) amplitude or glutamate receptor properties. Replenishing cholesterol restored Ca(V) channel domain size and release efficiency to control levels. These results indicate that cholesterol is important for organizing the cone active zone. Furthermore, the finding that cholesterol depletion impairs coupling between channel opening and vesicle release by allowing Ca(V) channels to move further from release sites shows that changes in presynaptic Ca(V) channel mobility can be a mechanism for adjusting synaptic strength.
Collapse
Affiliation(s)
- Aaron J Mercer
- Dept. of Ophthalmology and Visual Sciences, Univ. of Nebraska Medical Center, Omaha, NE 68198-5840, USA
| | | | | | | | | |
Collapse
|
43
|
Affiliation(s)
- Jim Berg
- Departments of Physiology, Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Huanghe Yang
- Departments of Physiology, Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94143, USA
| | - Lily Yeh Jan
- Departments of Physiology, Biochemistry and Biophysics, Howard Hughes Medical Institute, University of California, San Francisco, San Francisco, CA 94143, USA
| |
Collapse
|
44
|
Bartoletti TM, Jackman SL, Babai N, Mercer AJ, Kramer RH, Thoreson WB. Release from the cone ribbon synapse under bright light conditions can be controlled by the opening of only a few Ca(2+) channels. J Neurophysiol 2011; 106:2922-35. [PMID: 21880934 DOI: 10.1152/jn.00634.2011] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Light hyperpolarizes cone photoreceptors, causing synaptic voltage-gated Ca(2+) channels to open infrequently. To understand neurotransmission under these conditions, we determined the number of L-type Ca(2+) channel openings necessary for vesicle fusion at the cone ribbon synapse. Ca(2+) currents (I(Ca)) were activated in voltage-clamped cones, and excitatory postsynaptic currents (EPSCs) were recorded from horizontal cells in the salamander retina slice preparation. Ca(2+) channel number and single-channel current amplitude were calculated by mean-variance analysis of I(Ca). Two different comparisons-one comparing average numbers of release events to average I(Ca) amplitude and the other involving deconvolution of both EPSCs and simultaneously recorded cone I(Ca)-suggested that fewer than three Ca(2+) channel openings accompanied fusion of each vesicle at the peak of release during the first few milliseconds of stimulation. Opening fewer Ca(2+) channels did not enhance fusion efficiency, suggesting that few unnecessary channel openings occurred during strong depolarization. We simulated release at the cone synapse, using empirically determined synaptic dimensions, vesicle pool size, Ca(2+) dependence of release, Ca(2+) channel number, and Ca(2+) channel properties. The model replicated observations when a barrier was added to slow Ca(2+) diffusion. Consistent with the presence of a diffusion barrier, dialyzing cones with diffusible Ca(2+) buffers did not affect release efficiency. The tight clustering of Ca(2+) channels, along with a high-Ca(2+) affinity release mechanism and diffusion barrier, promotes a linear coupling between Ca(2+) influx and vesicle fusion. This may improve detection of small light decrements when cones are hyperpolarized by bright light.
Collapse
Affiliation(s)
- Theodore M Bartoletti
- Department of Ophthalmology and Visual Sciences, University of Nebraska Medical Center, Omaha, Nebraska 68198-5840, USA
| | | | | | | | | | | |
Collapse
|
45
|
Physiological roles and diseases of Tmem16/Anoctamin proteins: are they all chloride channels? Acta Pharmacol Sin 2011; 32:685-92. [PMID: 21642943 DOI: 10.1038/aps.2011.48] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The Tmem16 gene family was first identified by bioinformatic analysis in 2004. In 2008, it was shown independently by 3 laboratories that the first two members (Tmem16A and Tmem16B) of this 10-gene family are Ca(2+)-activated Cl(-) channels. Because these proteins are thought to have 8 transmembrane domains and be anion-selective channels, the alternative name, Anoctamin (anion and octa=8), has been proposed. However, it remains unclear whether all members of this family are, in fact, anion channels or have the same 8-transmembrane domain topology. Since 2008, there have been nearly 100 papers published on this gene family. The excitement about Tmem16 proteins has been enhanced by the finding that Ano1 has been linked to cancer, mutations in Ano5 are linked to several forms of muscular dystrophy (LGMDL2 and MMD-3), mutations in Ano10 are linked to autosomal recessive spinocerebellar ataxia, and mutations in Ano6 are linked to Scott syndrome, a rare bleeding disorder. Here we review some of the recent developments in understanding the physiology and structure-function of the Tmem16 gene family.
Collapse
|
46
|
Lateral mobility of presynaptic L-type calcium channels at photoreceptor ribbon synapses. J Neurosci 2011; 31:4397-406. [PMID: 21430141 DOI: 10.1523/jneurosci.5921-10.2011] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
At most synapses, presynaptic Ca(2+) channels are positioned near vesicle release sites, and increasing this distance reduces synaptic strength. We examined the lateral membrane mobility of presynaptic L-type Ca(2+) channels at photoreceptor ribbon synapses of the tiger salamander (Ambystoma tigrinum) retina. Movements of individual Ca(2+) channels were tracked by coupling quantum dots to an antibody against the extracellular α(2)δ(4) Ca(2+) channel subunit. α(2)δ(4) antibodies labeled photoreceptor terminals and colocalized with antibodies to synaptic vesicle glycoprotein 2 and voltage-gated Ca(2+) channel 1.4 (Ca(V)1.4) α(1) subunits. The results show that Ca(2+) channels are dynamic and move within a confined region beneath the synaptic ribbon. The size of this confinement area is regulated by actin and membrane cholesterol. Fusion of nearby synaptic vesicles caused jumps in Ca(2+) channel position, propelling them toward the outer edge of the confinement domain. Channels rebounded rapidly toward the center. Thus, although Ca(V) channels are mobile, molecular scaffolds confine them beneath the ribbon to maintain neurotransmission even at high release rates.
Collapse
|
47
|
Anoctamins. Pflugers Arch 2011; 462:195-208. [DOI: 10.1007/s00424-011-0975-9] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2011] [Revised: 05/04/2011] [Accepted: 05/04/2011] [Indexed: 01/14/2023]
|
48
|
Zampighi GA, Schietroma C, Zampighi LM, Woodruff M, Wright EM, Brecha NC. Conical tomography of a ribbon synapse: structural evidence for vesicle fusion. PLoS One 2011; 6:e16944. [PMID: 21390245 PMCID: PMC3046965 DOI: 10.1371/journal.pone.0016944] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Accepted: 01/18/2011] [Indexed: 12/04/2022] Open
Abstract
To characterize the sites of synaptic vesicle fusion in photoreceptors, we evaluated the three-dimensional structure of rod spherules from mice exposed to steady bright light or dark-adapted for periods ranging from 3 to 180 minutes using conical electron tomography. Conical tilt series from mice retinas were reconstructed using the weighted back projection algorithm, refined by projection matching and analyzed using semiautomatic density segmentation. In the light, rod spherules contained ∼470 vesicles that were hemi-fused and ∼187 vesicles that were fully fused (omega figures) with the plasma membrane. Active zones, defined by the presence of fully fused vesicles, extended along the entire area of contact between the rod spherule and the horizontal cell ending, and included the base of the ribbon, the slope of the synaptic ridge and ribbon-free regions apposed to horizontal cell axonal endings. There were transient changes of the rod spherules during dark adaptation. At early periods in the dark (3–15 minutes), there was a) an increase in the number of fully fused synaptic vesicles, b) a decrease in rod spherule volume, and c) an increase in the surface area of the contact between the rod spherule and horizontal cell endings. These changes partially compensate for the increase in the rod spherule plasma membrane following vesicle fusion. After 30 minutes of dark-adaptation, the rod spherules returned to dimensions similar to those measured in the light. These findings show that vesicle fusion occurs at both ribbon-associated and ribbon-free regions, and that transient changes in rod spherules and horizontal cell endings occur shortly after dark onset.
Collapse
Affiliation(s)
- Guido A. Zampighi
- Department of Neurobiology, David Geffen School of Medicine at UCLA, University of California Los Angeles, Los Angeles, California, United States of America
- Department of Physiology, David Geffen School of Medicine at UCLA, University of California Los Angeles, Los Angeles, California, United States of America
| | - Cataldo Schietroma
- Department of Neurobiology, David Geffen School of Medicine at UCLA, University of California Los Angeles, Los Angeles, California, United States of America
| | - Lorenzo M. Zampighi
- Department of Physiology, David Geffen School of Medicine at UCLA, University of California Los Angeles, Los Angeles, California, United States of America
| | - Michael Woodruff
- Integrative Biology and Physiology, College of Letters and Science, University of California Los Angeles, Los Angeles, California, United States of America
| | - Ernest M. Wright
- Department of Physiology, David Geffen School of Medicine at UCLA, University of California Los Angeles, Los Angeles, California, United States of America
| | - Nicholas C. Brecha
- Department of Neurobiology, David Geffen School of Medicine at UCLA, University of California Los Angeles, Los Angeles, California, United States of America
- Department of Medicine, David Geffen School of Medicine at UCLA, University of California Los Angeles, Los Angeles, California, United States of America
- Jules Stein Eye Institute, David Geffen School of Medicine at UCLA, University of California Los Angeles, Los Angeles, California, United States of America
- Veterans Administration Greater Los Angeles Healthcare System, Los Angeles, California, United States of America
- * E-mail:
| |
Collapse
|