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Takeuchi H, Kurahashi T. Segregation of Ca2+ signaling in olfactory signal transduction. J Gen Physiol 2023; 155:213865. [PMID: 36787110 PMCID: PMC9960254 DOI: 10.1085/jgp.202213165] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Revised: 11/04/2022] [Accepted: 01/13/2023] [Indexed: 02/15/2023] Open
Abstract
Olfactory signal transduction is conducted through a cAMP-mediated second messenger cascade. The cytoplasmic Ca2+ concentration increases through the opening of CNG channels, a phenomenon that underlies two major functions, namely, signal boosting and olfactory adaptation. Signal boosting is achieved by an additional opening of the Ca2+-activated Cl- channel whereas adaptation is regulated by Ca2+ feedback to the CNG channel. Thus, the influx of Ca2+ and the resultant increase in cytoplasmic Ca2+ levels play seemingly opposing effects: increasing the current while reducing the current through adaptation. The two functions could be interpreted as compensating for each other. However, in real cells, both functions should be segregated. Ca2+ dynamics in olfactory cilia need to be directly measured, but technical difficulties accompanying the thin structure of olfactory cilia have prevented systematic analyses. In this study, using a combination of electrophysiology, local photolysis of caged cAMP, and Ca2+ imaging, we found that free Ca2+ in the local ciliary cytoplasm decreased along with a reduction in the current containing Ca2+-activated Cl- components returning to the basal level, whereas Ca2+-dependent adaptation persisted for a longer period. The activity of Cl- channels is highly likely to be regulated by the free Ca2+ that is present only immediately after the influx through the CNG channel, and an exclusive interaction between Ca2+ and Ca2+-binding proteins that mediate the adaptation may modulate the adaptation lifetime.
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Affiliation(s)
- Hiroko Takeuchi
- Department of Biophysical Dynamics, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
- Correspondence to Hiroko Takeuchi:
| | - Takashi Kurahashi
- Department of Biophysical Dynamics, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan
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Boccaccio A, Menini A, Pifferi S. The cyclic AMP signaling pathway in the rodent main olfactory system. Cell Tissue Res 2021; 383:429-443. [PMID: 33447881 DOI: 10.1007/s00441-020-03391-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2020] [Accepted: 12/10/2020] [Indexed: 01/15/2023]
Abstract
Odor perception begins with the detection of odorant molecules by the main olfactory epithelium located in the nasal cavity. Odorant molecules bind to and activate a large family of G-protein-coupled odorant receptors and trigger a cAMP-mediated transduction cascade that converts the chemical stimulus into an electrical signal transmitted to the brain. Morever, odorant receptors and cAMP signaling plays a relevant role in olfactory sensory neuron development and axonal targeting to the olfactory bulb. This review will first explore the physiological response of olfactory sensory neurons to odorants and then analyze the different components of cAMP signaling and their different roles in odorant detection and olfactory sensory neuron development.
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Affiliation(s)
- Anna Boccaccio
- Institute of Biophysics, National Research Council (CNR), Genova, Italy.
| | - Anna Menini
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, Italy
| | - Simone Pifferi
- Neurobiology Group, SISSA, Scuola Internazionale Superiore di Studi Avanzati, Trieste, Italy.,Department of Experimental and Clinical Medicine, Università Politecnica delle Marche, Ancona, Italy
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3
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Takeuchi H, Kurahashi T. Second messenger molecules have a limited spread in olfactory cilia. J Gen Physiol 2018; 150:1647-1659. [PMID: 30352795 PMCID: PMC6279364 DOI: 10.1085/jgp.201812126] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2018] [Revised: 08/12/2018] [Accepted: 10/03/2018] [Indexed: 01/12/2023] Open
Abstract
Olfactory responses in the cilia of olfactory receptor cells last for longer than 10 s, which cannot be explained by free diffusion of second messengers. Takeuchi and Kurahashi show that these signaling molecules have a limited spread and remain at the site of generation for a long time. Odorants are detected by olfactory receptors on the sensory cilia of olfactory receptor cells (ORCs). These cylindrical cilia have a diameters of 100–200 nm, within which the components required for signal transduction by the adenylyl cyclase–cAMP system are located. The kinetics of odorant responses are determined by the lifetimes of active proteins as well as the production, diffusion, and extrusion/degradation of second messenger molecules (cAMP and Ca2+). However, there is limited information about the molecular kinetics of ORC responses, mostly because of the technical limitations involved in studying such narrow spaces and fine structures. In this study, using a combination of electrophysiology, photolysis of caged substances, and spot UV laser stimulation, we show that second messenger molecules work only in the vicinity of their site of generation in the olfactory cilia. Such limited spreading clearly explains a unique feature of ORCs, namely, the integer multiple of unitary events that they display in low Ca2+ conditions. Although the small ORC uses cAMP and Ca2+ for various functions in different regions of the cell, these substances seem to operate only in the compartment that has been activated by the appropriate stimulus. We also show that these substances remain in the same vicinity for a long time. This enables the ORC to amplify the odorant signal and extend the lifetime of Ca2+-dependent adaptation. Cytoplasmic buffers and extrusion/degradation systems seem to play a crucial role in limiting molecular spreading. In addition, binding sites on the cytoplasmic surface of the plasma membrane may limit molecular diffusion in such a narrow space because of the high surface/volume ratio. Such efficient energy conversion may also be broadly used in other biological systems that have not yet been subjected to systematic experiments.
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Affiliation(s)
- Hiroko Takeuchi
- Department of Biophysical Dynamics, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
| | - Takashi Kurahashi
- Department of Biophysical Dynamics, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
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4
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Henkel B, Drose DR, Ackels T, Oberland S, Spehr M, Neuhaus EM. Co-expression of anoctamins in cilia of olfactory sensory neurons. Chem Senses 2014; 40:73-87. [PMID: 25500808 DOI: 10.1093/chemse/bju061] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Vertebrates can sense and identify a vast array of chemical cues. The molecular machinery involved in chemodetection and transduction is expressed within the cilia of olfactory sensory neurons. Currently, there is only limited information available on the distribution and density of individual signaling components within the ciliary compartment. Using super-resolution microscopy, we show here that cyclic-nucleotide-gated channels and calcium-activated chloride channels of the anoctamin family are localized to discrete microdomains in the ciliary membrane. In addition to ANO2, a second anoctamin, ANO6, also localizes to ciliary microdomains. This observation, together with the fact that ANO6 and ANO2 co-localize, indicates a role for ANO6 in olfactory signaling. We show that both ANO2 and ANO6 can form heteromultimers and that this heteromerization alters the recombinant channels' physiological properties. Thus, we provide evidence for interaction of ANO2 and ANO6 in olfactory cilia, with possible physiological relevance for olfactory signaling.
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Affiliation(s)
- Bastian Henkel
- Department of Pharmacology and Toxicology, University Hospital Jena, Drackendorfer Strasse 1, 07747 Jena, Germany, Cluster of Excellence NeuroCure, Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany, FU Berlin, Fachbereich Biologie, Chemie und Pharmazie , Takustr. 3, 14195 Berlin, Germany and
| | - Daniela R Drose
- Department of Chemosensation, Institute for Biology II, RWTH Aachen University, Worringerweg 3, 52074 Aachen, Germany
| | - Tobias Ackels
- Department of Chemosensation, Institute for Biology II, RWTH Aachen University, Worringerweg 3, 52074 Aachen, Germany
| | - Sonja Oberland
- Department of Pharmacology and Toxicology, University Hospital Jena, Drackendorfer Strasse 1, 07747 Jena, Germany, Cluster of Excellence NeuroCure, Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany, FU Berlin, Fachbereich Biologie, Chemie und Pharmazie , Takustr. 3, 14195 Berlin, Germany and
| | - Marc Spehr
- Department of Chemosensation, Institute for Biology II, RWTH Aachen University, Worringerweg 3, 52074 Aachen, Germany
| | - Eva M Neuhaus
- Department of Pharmacology and Toxicology, University Hospital Jena, Drackendorfer Strasse 1, 07747 Jena, Germany, Cluster of Excellence NeuroCure, Charité-Universitätsmedizin Berlin, Charitéplatz 1, 10117 Berlin, Germany,
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Frenz CT, Hansen A, Dupuis ND, Shultz N, Levinson SR, Finger TE, Dionne VE. NaV1.5 sodium channel window currents contribute to spontaneous firing in olfactory sensory neurons. J Neurophysiol 2014; 112:1091-104. [PMID: 24872539 DOI: 10.1152/jn.00154.2014] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Olfactory sensory neurons (OSNs) fire spontaneously as well as in response to odor; both forms of firing are physiologically important. We studied voltage-gated Na(+) channels in OSNs to assess their role in spontaneous activity. Whole cell patch-clamp recordings from OSNs demonstrated both tetrodotoxin-sensitive and tetrodotoxin-resistant components of Na(+) current. RT-PCR showed mRNAs for five of the nine different Na(+) channel α-subunits in olfactory tissue; only one was tetrodotoxin resistant, the so-called cardiac subtype NaV1.5. Immunohistochemical analysis indicated that NaV1.5 is present in the apical knob of OSN dendrites but not in the axon. The NaV1.5 channels in OSNs exhibited two important features: 1) a half-inactivation potential near -100 mV, well below the resting potential, and 2) a window current centered near the resting potential. The negative half-inactivation potential renders most NaV1.5 channels in OSNs inactivated at the resting potential, while the window current indicates that the minor fraction of noninactivated NaV1.5 channels have a small probability of opening spontaneously at the resting potential. When the tetrodotoxin-sensitive Na(+) channels were blocked by nanomolar tetrodotoxin at the resting potential, spontaneous firing was suppressed as expected. Furthermore, selectively blocking NaV1.5 channels with Zn(2+) in the absence of tetrodotoxin also suppressed spontaneous firing, indicating that NaV1.5 channels are required for spontaneous activity despite resting inactivation. We propose that window currents produced by noninactivated NaV1.5 channels are one source of the generator potentials that trigger spontaneous firing, while the upstroke and propagation of action potentials in OSNs are borne by the tetrodotoxin-sensitive Na(+) channel subtypes.
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Affiliation(s)
| | - Anne Hansen
- Department of Cellular and Developmental Biology, Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Anschutz Medical Center, Aurora, Colorado; and
| | | | - Nicole Shultz
- Department of Cellular and Developmental Biology, Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Anschutz Medical Center, Aurora, Colorado; and
| | - Simon R Levinson
- Department of Physiology and Biophysics, University of Colorado School of Medicine, Anschutz Medical Center, Aurora, Colorado
| | - Thomas E Finger
- Department of Cellular and Developmental Biology, Rocky Mountain Taste and Smell Center, University of Colorado School of Medicine, Anschutz Medical Center, Aurora, Colorado; and
| | - Vincent E Dionne
- Department of Biology, Boston University, Boston, Massachusetts;
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2,4,6-trichloroanisole is a potent suppressor of olfactory signal transduction. Proc Natl Acad Sci U S A 2013; 110:16235-40. [PMID: 24043819 DOI: 10.1073/pnas.1300764110] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We investigated the sensitivity of single olfactory receptor cells to 2,4,6-trichloroanisole (TCA), a compound known for causing cork taint in wines. Such off-flavors have been thought to originate from unpleasant odor qualities evoked by contaminants. However, we here show that TCA attenuates olfactory transduction by suppressing cyclic nucleotide-gated channels, without evoking odorant responses. Surprisingly, suppression was observed even at extremely low (i.e., attomolar) TCA concentrations. The high sensitivity to TCA was associated with temporal integration of the suppression effect. We confirmed that potent suppression by TCA and similar compounds was correlated with their lipophilicity, as quantified by the partition coefficient at octanol/water boundary (pH 7.4), suggesting that channel suppression is mediated by a partitioning of TCA into the lipid bilayer of plasma membranes. The rank order of suppression matched human recognition of off-flavors: TCA equivalent to 2,4,6-tribromoanisole, which is much greater than 2,4,6-trichlorophenol. Furthermore, TCA was detected in a wide variety of foods and beverages surveyed for odor losses. Our findings demonstrate a potential molecular mechanism for the reduction of flavor.
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Wojtyniak M, Brear AG, O'Halloran DM, Sengupta P. Cell- and subunit-specific mechanisms of CNG channel ciliary trafficking and localization in C. elegans. J Cell Sci 2013; 126:4381-95. [PMID: 23886944 DOI: 10.1242/jcs.127274] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Primary cilia are ubiquitous sensory organelles that concentrate transmembrane signaling proteins essential for sensing environmental cues. Mislocalization of crucial ciliary signaling proteins, such as the tetrameric cyclic nucleotide-gated (CNG) channels, can lead to cellular dysfunction and disease. Although several cis- and trans-acting factors required for ciliary protein trafficking and localization have been identified, whether these mechanisms act in a protein- and cell-specific manner is largely unknown. Here, we show that CNG channel subunits can be localized to discrete ciliary compartments in individual sensory neurons in C. elegans, suggesting that channel composition is heterogeneous across the cilium. We demonstrate that ciliary localization of CNG channel subunits is interdependent on different channel subunits in specific cells, and identify sequences required for efficient ciliary targeting and localization of the TAX-2 CNGB and TAX-4 CNGA subunits. Using a candidate gene approach, we show that Inversin, transition zone proteins, intraflagellar transport motors and a MYND-domain protein are required to traffic and/or localize CNG channel subunits in both a cell- and channel subunit-specific manner. We further find that TAX-2 and TAX-4 are relatively immobile in specific sensory cilia subcompartments, suggesting that these proteins undergo minimal turnover in these domains in mature cilia. Our results uncover unexpected diversity in the mechanisms that traffic and localize CNG channel subunits to cilia both within and across cell types, highlighting the essential contribution of this process to cellular functions.
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Affiliation(s)
- Martin Wojtyniak
- Department of Biology and National Center for Behavioral Genomics, Brandeis University, Waltham, MA 02454, USA
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Abstract
BACKGROUND Most cells in the body possess a single primary cilium. These cilia are key transducers of sensory stimuli, and defects in cilia have been linked to several diseases. Evidence suggests that some transduction of sensory stimuli by the primary cilium depends on ion-conducting channels. However, the tiny size of the cilium has been a critical barrier to understanding its electrical properties. We report a novel method that allows sensitive, repeatable electrical recordings from primary cilia. Adherent cells were grown on small, spherical beads that could be easily moved within the recording chamber. In this configuration, an entire cilium could be pulled into a recording microelectrode. RESULTS In 47% of attempts, suction resulted in a seal with high input resistance. Single channels could be recorded while the cilium remained attached to the cell. When the pipette was raised into the air, the cell body was pulled off at the air-bath interface. The pipette retained the cilium and could then be immersed in various solutions that bathed the cytoplasmic face of the membrane. In excised cilia, ionic currents through ciliary channels were modulated by cytoplasmic Ca(2+) and transmembrane voltage. CONCLUSIONS Ciliary recording is a direct way to learn the effects of second messengers and voltage changes on ciliary transduction channels.
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Nakashima N, Ishii TM, Bessho Y, Kageyama R, Ohmori H. Hyperpolarisation-activated cyclic nucleotide-gated channels regulate the spontaneous firing rate of olfactory receptor neurons and affect glomerular formation in mice. J Physiol 2013; 591:1749-69. [PMID: 23318872 DOI: 10.1113/jphysiol.2012.247361] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Olfactory receptor neurons (ORNs), which undergo lifelong neurogenesis, have been studied extensively to understand how neurons form precise topographical networks. Neural projections from ORNs are principally guided by the genetic code, which directs projections from ORNs that express a specific odorant receptor to the corresponding glomerulus in the olfactory bulb. In addition, ORNs utilise spontaneous firing activity to establish and maintain the neural map. However, neither the process of generating this spontaneous activity nor its role as a guidance cue in the olfactory bulb is clearly understood. Utilising extracellular unit-recordings in mouse olfactory epithelium slices, we demonstrated that the hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels in the somas of ORNs depolarise their membranes and boost their spontaneous firing rates by sensing basal cAMP levels; the odorant-sensitive cyclic nucleotide-gated (CNG) channels in cilia do not. The basal cAMP levels were maintained via the standing activation of β-adrenergic receptors. Using a Tet-off system to over-express HCN4 channels resulted in the enhancement of spontaneous ORN activity and dramatically reduced both the size and number of glomeruli in the olfactory bulb. This phenotype was rescued by the administration of doxycycline. These findings suggest that cAMP plays different roles in cilia and soma and that basal cAMP levels in the soma are directly converted via HCN channels into a spontaneous firing frequency that acts as an intrinsic guidance cue for the formation of olfactory networks.
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Affiliation(s)
- Noriyuki Nakashima
- Department of Physiology, Faculty of Medicine, Kyoto University, Yoshida-Konoe, Sakyo-ku, Kyoto 606-8501, Japan.
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Matsumura K, Matsumoto M, Kurahashi T, Takeuchi H. Recordings from cultured newt olfactory receptor cells. Zoolog Sci 2012; 29:340-5. [PMID: 22559969 DOI: 10.2108/zsj.29.340] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Freshly dissociated olfactory receptor cells (ORCs) are commonly used in electrophysiological research investigations of the physicochemical mechanisms of olfactory signal transduction. Because the morphology of cultured cells clearly becomes worse over time, the ORCs are examined traditionally within several days after dissociation. However, there has been a major concern that cells are affected soon after dissociation. To gain a better understanding of the reliability of data obtained from solitary cells, we obtained electrical data during the lifetime of single ORCs dissociated from the newt. The time course for the deterioration could be revealed by monitoring the membrane properties during culture. Although the number of living cells that were identified by trypan blue extrusion declined day by day, the remaining cells retained morphology and their fundamental electrical features until day 19. In some cells, the cilia and dendrite were observed until day 21, and the bipolar morphology until day 31. The fundamental features of cell excitation were maintained during culture without showing remarkable changes when they retained morphological features. The results suggest that electrical properties of cells are almost unchanged within several days. Furthermore, the dissociated newt ORCs can be used for several weeks that are almost comparable to the intrinsic lifetime of the ORCs in vivo.
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Affiliation(s)
- Kyohei Matsumura
- Graduate School of Frontier Biosciences, Osaka University, Toyonaka, Osaka 560-8531, Japan
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Alevra M, Schwartz P, Schild D. Direct measurement of diffusion in olfactory cilia using a modified FRAP approach. PLoS One 2012; 7:e39628. [PMID: 22808046 PMCID: PMC3393724 DOI: 10.1371/journal.pone.0039628] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2012] [Accepted: 05/29/2012] [Indexed: 11/19/2022] Open
Abstract
The diffusion coefficient of fluorescein in detached cilia of Xenopus laevis olfactory receptor neurons was measured using spatially-resolved FRAP, where the dye along half of the ciliary length was photobleached and its spatiotemporal fluorescence redistribution recorded. Fitting a one-dimensional numerical simulation of diffusion and photobleaching for 35 cilia resulted in a mean value of the diffusion coefficient and thus a reduction by a factor of compared to free diffusion in aqueous solution.
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Affiliation(s)
- Mihai Alevra
- Department of Neurophysiology and Cellular Biophysics, University of Göttingen, Göttingen, Germany.
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Abstract
Sodium (Na) toxicity is one of the most formidable challenges for crop production world-wide. Nevertheless, despite decades of intensive research, the pathways of Na(+) entry into the roots of plants under high salinity are still not definitively known. Here, we review critically the current paradigms in this field. In particular, we explore the evidence supporting the role of nonselective cation channels, potassium transporters, and transporters from the HKT family in primary sodium influx into plant roots, and their possible roles elsewhere. We furthermore discuss the evidence for the roles of transporters from the NHX and SOS families in intracellular Na(+) partitioning and removal from the cytosol of root cells. We also review the literature on the physiology of Na(+) fluxes and cytosolic Na(+) concentrations in roots and invite critical interpretation of seminal published data in these areas. The main focus of the review is Na(+) transport in glycophytes, but reference is made to literature on halophytes where it is essential to the analysis.
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French DA, Badamdorj D, Kleene SJ. Spatial distribution of calcium-gated chloride channels in olfactory cilia. PLoS One 2010; 5:e15676. [PMID: 21209888 PMCID: PMC3012700 DOI: 10.1371/journal.pone.0015676] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2010] [Accepted: 11/21/2010] [Indexed: 11/18/2022] Open
Abstract
Background In vertebrate olfactory receptor neurons, sensory cilia transduce odor stimuli into changes in neuronal membrane potential. The voltage changes are primarily caused by the sequential openings of two types of channel: a cyclic-nucleotide-gated (CNG) cationic channel and a calcium-gated chloride channel. In frog, the cilia are 25 to 200 µm in length, so the spatial distributions of the channels may be an important determinant of odor sensitivity. Principal Findings To determine the spatial distribution of the chloride channels, we recorded from single cilia as calcium was allowed to diffuse down the length of the cilium and activate the channels. A computational model of this experiment allowed an estimate of the spatial distribution of the chloride channels. On average, the channels were concentrated in a narrow band centered at a distance of 29% of the ciliary length, measured from the base of the cilium. This matches the location of the CNG channels determined previously. This non-uniform distribution of transduction proteins is consistent with similar findings in other cilia. Conclusions On average, the two types of olfactory transduction channel are concentrated in the same region of the cilium. This may contribute to the efficient detection of weak stimuli.
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Affiliation(s)
- Donald A. French
- Department of Mathematical Sciences, University of Cincinnati, Cincinnati, Ohio, United States of America
| | - Dorjsuren Badamdorj
- Department of Mathematical Sciences, University of Cincinnati, Cincinnati, Ohio, United States of America
| | - Steven J. Kleene
- Department of Cancer and Cell Biology, University of Cincinnati, Cincinnati, Ohio, United States of America
- * E-mail:
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Abstract
An important contributing factor for the high sensitivity of sensory systems is the exquisite sensitivity of the sensory receptor cells. We report here the signaling threshold of the olfactory receptor neuron (ORN). We first obtained a best estimate of the size of the physiological electrical response successfully triggered by a single odorant-binding event on a frog ORN, which was ∼0.034 pA and had an associated transduction domain spanning only a tiny fraction of the length of an ORN cilium. We also estimated the receptor-current threshold for an ORN to fire action potentials in response to an odorant pulse, which was ∼1.2 pA. Thus, it takes about 35 odorant-binding events successfully triggering transduction during a brief odorant pulse in order for an ORN to signal to the brain.
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Castillo K, Restrepo D, Bacigalupo J. Cellular and molecular Ca2+ microdomains in olfactory cilia support low signaling amplification of odor transduction. Eur J Neurosci 2010; 32:932-8. [PMID: 20849528 DOI: 10.1111/j.1460-9568.2010.07393.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Signal transduction depends critically on the spatial localization of protein constituents. A key question in odor transduction is whether chemotransduction proteins organize into discrete molecular complexes throughout olfactory cilia or distribute homogeneously along the ciliary membrane. Our recordings of Ca(2+) changes in individual cilia with unprecedented spatial and temporal resolution, by the use of two-photon microscopy, provide solid evidence for Ca(2+) microdomains (transducisomes). Dissociated frog olfactory neurons were preloaded with caged-cAMP and fluo-4 acetoxymethyl ester probe Ca(2+) indicator. Ca(2+) influx through cyclic nucleotide-gated (CNG) channels was evoked by uniformly photoreleasing cAMP, while ciliary Ca(2+) was measured. Discrete fluorescence events were clearly resolved. Events were missing in the absence of external Ca(2+) , consistent with the absence of internal Ca(2+) sources. Fluorescence events at individual microdomains resembled single-CNG channel fluctuations in shape, mean duration and kinetics, indicating that transducisomes typically contain one to three CNG channels. Inhibiting the Na(+) /Ca(2+) exchanger or the Ca(2+) -ATPase prolonged the decay of evoked intraciliary Ca(2+) transients, supporting the participation of both transporters in ciliary Ca(2+) clearance, and suggesting that both molecules localize close to the CNG channel. Chemosensory transducisomes provide a physical basis for the low amplification and for the linearity of odor responses at low odor concentrations.
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Affiliation(s)
- Karen Castillo
- Department of Biology, Faculty of Sciences, University of Chile, Santiago, Las Palmeras 3525, Nuñoa, Santiago 7800024
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The endocannabinoid 2-arachidonoyl-glycerol controls odor sensitivity in larvae of Xenopus laevis. J Neurosci 2010; 30:8965-73. [PMID: 20592217 DOI: 10.1523/jneurosci.4030-09.2010] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Cannabinoids modulate the activity of many neuronal cells, among them sensory neurons in the olfactory epithelium. Here we show that the endocannabinoid 2-arachidonoyl-glycerol (2-AG) is synthesized in both olfactory receptor neurons and glia-like sustentacular cells in larval Xenopus laevis. Its production in the latter depends on the hunger state of the animal. The essential effect of 2-AG in olfactory receptor neurons is the control of odorant detection thresholds via cannabinoid CB(1) receptor activation. Hunger renders olfactory neurons more sensitive. Endocannabinoid modulation in the nose may therefore substantially influence food-seeking behavior.
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The endocannabinoid 2-arachidonoyl-glycerol controls odor sensitivity in larvae of Xenopus laevis. J Neurosci 2010. [PMID: 20592217 DOI: 10.1523/jneurosci.4030‐09.2010] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Cannabinoids modulate the activity of many neuronal cells, among them sensory neurons in the olfactory epithelium. Here we show that the endocannabinoid 2-arachidonoyl-glycerol (2-AG) is synthesized in both olfactory receptor neurons and glia-like sustentacular cells in larval Xenopus laevis. Its production in the latter depends on the hunger state of the animal. The essential effect of 2-AG in olfactory receptor neurons is the control of odorant detection thresholds via cannabinoid CB(1) receptor activation. Hunger renders olfactory neurons more sensitive. Endocannabinoid modulation in the nose may therefore substantially influence food-seeking behavior.
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Abstract
Most neurons possess a single, nonmotile cilium that projects out from the cell surface. These microtubule-based organelles are important in brain development and neurogenesis; however, their function in mature neurons is unknown. Cilia express a complement of proteins distinct from other neuronal compartments, one of which is the somatostatin receptor subtype SST(3). We show here that SST(3) is critical for object recognition memory in mice. sst3 knock-out mice are severely impaired in discriminating novel objects, whereas they retain normal memory for object location. Further, systemic injection of an SST(3) antagonist (ACQ090) disrupts recall of familiar objects in wild-type mice. To examine mechanisms of SST(3), we tested synaptic plasticity in CA1 hippocampus. Electrically evoked long-term potentiation (LTP) was normal in sst3 knock-out mice, while adenylyl cyclase/cAMP-mediated LTP was impaired. The SST(3) antagonist also disrupted cAMP-mediated LTP. Basal cAMP levels in hippocampal lysate were reduced in sst3 knock-out mice compared with wild-type mice, while the forskolin-induced increase in cAMP levels was normal. The SST(3) antagonist inhibited forskolin-stimulated cAMP increases, whereas the SST(3) agonist L-796,778 increased basal cAMP levels in hippocampal slices but not hippocampal lysate. Our results show that somatostatin signaling in neuronal cilia is critical for recognition memory and suggest that the cAMP pathway is a conserved signaling motif in cilia. Neuronal cilia therefore represent a novel nonsynaptic compartment crucial for signaling involved in a specific form of synaptic plasticity and in novelty detection.
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Inoue R, Nakatani K. Changes in the Olfactory Response to Amino Acids in Japanese Newts After Transfer from an Aquatic to a Terrestrial Habitat. Zoolog Sci 2010; 27:369-73. [DOI: 10.2108/zsj.27.369] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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Dan Y, Cao Y, Mallouk TE, Evoy S, Johnson ATC. Gas sensing properties of single conducting polymer nanowires and the effect of temperature. NANOTECHNOLOGY 2009; 20:434014. [PMID: 19801757 DOI: 10.1088/0957-4484/20/43/434014] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
We measured the electronic properties and gas sensing responses of template-grown poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS)-based nanowires. The nanowires had a 'striped' structure (gold-PEDOT/PSS-gold), and were typically 8 microm long (1 microm-6 microm-1 microm for the sections, respectively) and 220 nm in diameter. Single-nanowire devices were contacted with pre-fabricated gold electrodes using dielectrophoretic assembly. A polymer conductivity of 11.5 +/- 0.7 S cm(-1) and a contact resistance of 27.6 +/- 4 kOmega were inferred from measurements on nanowires of varying length and diameter. The nanowire sensors detected a variety of odors, with rapid response and recovery (seconds). The response (DeltaR/R) varied as a power law with analyte concentration. The power law exponent was found to increase with the molecular weight of the analyte and as a function of temperature. The detection limits are set by noise intrinsic to the device and are at the ppm level even for very volatile analytes.
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Affiliation(s)
- Yaping Dan
- Department of Electrical Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA
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Takeuchi H, Ishida H, Hikichi S, Kurahashi T. Mechanism of olfactory masking in the sensory cilia. J Gen Physiol 2009; 133:583-601. [PMID: 19433623 PMCID: PMC2713142 DOI: 10.1085/jgp.200810085] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2008] [Accepted: 04/22/2009] [Indexed: 12/02/2022] Open
Abstract
Olfactory masking has been used to erase the unpleasant sensation in human cultures for a long period of history. Here, we show a positive correlation between the human masking and the odorant suppression of the transduction current through the cyclic nucleotide-gated (CNG) and Ca2+-activated Cl- (Cl(Ca)) channels. Channels in the olfactory cilia were activated with the cytoplasmic photolysis of caged compounds, and their sensitiveness to odorant suppression was measured with the whole cell patch clamp. When 16 different types of chemicals were applied to cells, cyclic AMP (cAMP)-induced responses (a mixture of CNG and Cl(Ca) currents) were suppressed widely with these substances, but with different sensitivities. Using the same chemicals, in parallel, we measured human olfactory masking with 6-rate scoring tests and saw a correlation coefficient of 0.81 with the channel block. Ringer's solution that was just preexposed to the odorant-containing air affected the cAMP-induced current of the single cell, suggesting that odorant suppression occurs after the evaporation and air/water partition of the odorant chemicals at the olfactory mucus. To investigate the contribution of Cl(Ca), the current was exclusively activated by using the ultraviolet photolysis of caged Ca, DM-nitrophen. With chemical stimuli, it was confirmed that Cl(Ca) channels were less sensitive to the odorant suppression. It is interpreted, however, that in the natural odorant response the Cl(Ca) is affected by the reduction of Ca2+ influx through the CNG channels as a secondary effect. Because the signal transmission between CNG and Cl(Ca) channels includes nonlinear signal-boosting process, CNG channel blockage leads to an amplified reduction in the net current. In addition, we mapped the distribution of the Cl(Ca) channel in living olfactory single cilium using a submicron local [Ca2+]i elevation with the laser photolysis. Cl(Ca) channels are expressed broadly along the cilia. We conclude that odorants regulate CNG level to express masking, and Cl(Ca) in the cilia carries out the signal amplification and reduction evenly spanning the entire cilia. The present findings may serve possible molecular architectures to design effective masking agents, targeting olfactory manipulation at the nano-scale ciliary membrane.
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Affiliation(s)
- Hiroko Takeuchi
- Graduate School of Frontier Biosciences, Osaka University, Osaka 560-8531, Japan
| | - Hirohiko Ishida
- Perfumery Development Research Laboratories, Kao Corporation, Tokyo, 131-8501, Japan
| | - Satoshi Hikichi
- Perfumery Development Research Laboratories, Kao Corporation, Tokyo, 131-8501, Japan
| | - Takashi Kurahashi
- Graduate School of Frontier Biosciences, Osaka University, Osaka 560-8531, Japan
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Kleene SJ. Limits of calcium clearance by plasma membrane calcium ATPase in olfactory cilia. PLoS One 2009; 4:e5266. [PMID: 19390572 PMCID: PMC2668752 DOI: 10.1371/journal.pone.0005266] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2009] [Accepted: 03/24/2009] [Indexed: 12/02/2022] Open
Abstract
Background In any fine sensory organelle, a small influx of Ca2+ can quickly elevate cytoplasmic Ca2+. Mechanisms must exist to clear the ciliary Ca2+ before it reaches toxic levels. One such organelle has been well studied: the vertebrate olfactory cilium. Recent studies have suggested that clearance from the olfactory cilium is mediated in part by plasma membrane Ca2+-ATPase (PMCA). Principal Findings In the present study, electrophysiological assays were devised to monitor cytoplasmic free Ca2+ in single frog olfactory cilia. Ca2+ was allowed to enter isolated cilia, either through the detached end or through membrane channels. Intraciliary Ca2+ was monitored via the activity of ciliary Ca2+-gated Cl− channels, which are sensitive to free Ca2+ from about 2 to 10 µM. No significant effect of MgATP on intraciliary free Ca2+ could be found. Carboxyeosin, which has been used to inhibit PMCA, was found to substantially increase a ciliary transduction current activated by cyclic AMP. This increase was ATP-independent. Conclusions Alternative explanations are suggested for two previous experiments taken to support a role for PMCA in ciliary Ca2+ clearance. It is concluded that PMCA in the cilium plays a very limited role in clearing the micromolar levels of intraciliary Ca2+ produced during the odor response.
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Affiliation(s)
- Steven J Kleene
- Department of Cancer and Cell Biology, University of Cincinnati, Cincinnati, Ohio, United States of America.
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Kleene SJ. The electrochemical basis of odor transduction in vertebrate olfactory cilia. Chem Senses 2008; 33:839-59. [PMID: 18703537 DOI: 10.1093/chemse/bjn048] [Citation(s) in RCA: 143] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Most vertebrate olfactory receptor neurons share a common G-protein-coupled pathway for transducing the binding of odorant into depolarization. The depolarization involves 2 currents: an influx of cations (including Ca2+) through cyclic nucleotide-gated channels and a secondary efflux of Cl- through Ca2+-gated Cl- channels. The relation between stimulus strength and receptor current shows positive cooperativity that is attributed to the channel properties. This cooperativity amplifies the responses to sufficiently strong stimuli but reduces sensitivity and dynamic range. The odor response is transient, and prolonged or repeated stimulation causes adaptation and desensitization. At least 10 mechanisms may contribute to termination of the response; several of these result from an increase in intraciliary Ca2+. It is not known to what extent regulation of ionic concentrations in the cilium depends on the dendrite and soma. Although many of the major mechanisms have been identified, odor transduction is not well understood at a quantitative level.
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Affiliation(s)
- Steven J Kleene
- Department of Cancer and Cell Biology, University of Cincinnati, PO Box 670667, 231 Albert Sabin Way, Cincinnati, OH 45267-0667, USA.
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Mukhopadhyay S, Lu Y, Shaham S, Sengupta P. Sensory signaling-dependent remodeling of olfactory cilia architecture in C. elegans. Dev Cell 2008; 14:762-74. [PMID: 18477458 DOI: 10.1016/j.devcel.2008.03.002] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2007] [Revised: 01/21/2008] [Accepted: 03/03/2008] [Indexed: 10/22/2022]
Abstract
Nonmotile primary cilia are sensory organelles composed of a microtubular axoneme and a surrounding membrane sheath that houses signaling molecules. Optimal cellular function requires the precise regulation of axoneme assembly, membrane biogenesis, and signaling protein targeting and localization via as yet poorly understood mechanisms. Here, we show that sensory signaling is required to maintain the architecture of the specialized AWB olfactory neuron cilia in C. elegans. Decreased sensory signaling results in alteration of axoneme length and expansion of a membraneous structure, thereby altering the topological distribution of a subset of ciliary transmembrane signaling molecules. Signaling-regulated alteration of ciliary structures can be bypassed by modulation of intracellular cGMP or calcium levels and requires kinesin-II-driven intraflagellar transport (IFT), as well as BBS- and RAB8-related proteins. Our results suggest that compensatory mechanisms in response to altered levels of sensory activity modulate AWB cilia architecture, revealing remarkable plasticity in the regulation of cilia structure.
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Affiliation(s)
- Saikat Mukhopadhyay
- Department of Biology and National Center for Behavioral Genomics, Brandeis University, Waltham, MA 02454, USA
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