Calcium‐activated chloride currents in olfactory sensory neurons from mice lacking bestrophin‐2

Pifferi, Simone; Dibattista, Michele; Sagheddu, Claudia; Boccaccio, Anna; Qteishat, Ahmed Al; Ghirardi, Filippo; Tirindelli, Roberto; Menini, Anna

doi:10.1113/jphysiol.2009.176131

Cited by 47 publications

(41 citation statements)

References 55 publications

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“…6). As observed previously 12,35 , Ano2 +/+ neurons responded to uncaging of Ca 2+ with large, rapidly activating, transient currents that reversed close to the Clequilibrium potential (Fig. 6a,c).…”

Section: No Change Of Key Proteins and Axonal Convergencesupporting

confidence: 84%

“…An important role for Cl -in olfaction was also inferred from EOGs 11,16,37 . However, as the molecular identity of the olfactory Ca 2+ -activated Cl -channel has remained elusive 35 , the role of Cl -channels in olfaction could not be tested directly. The present work unambiguously identifies Ano2 as olfactory Ca 2+ -activated Clchannel, or at least as an essential component thereof.…”

Section: Discussionmentioning

confidence: 99%

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Ca2+-activated Cl− currents are dispensable for olfaction

et al. 2011

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Graduate student at the Freie Universität Berlin Olfaction in mammals involves the binding of odorants to a subset of the large number of different G protein-coupled receptors that are present in the cilia of olfactory sensory neurons (OSNs) 1 . These neurons are predominantly found in the MOE, which senses and discriminates myriad volatile compounds. In the mouse, the nose contains additional, apparently more specialized olfactory organs, such the septal organ of Masera and the VNO 2 . Sensory neurons in the VNO are morphologically distinct and use odorant receptors and signal transduction cascades that differ from those found in the MOE.In the canonical OSN signal transduction pathway, odorant binding to the receptor locally increases cytosolic cAMP through activation of the olfactory G protein G olf and adenylate cyclase type III 1,2 . cAMP then opens heteromeric cyclic nucleotide-gated (CNG) cation channels 3 . The resulting influx of Na + and Ca 2+ depolarizes the plasma membrane and raises the cytosolic Ca 2+ concentration ([Ca 2+ ] i ), thereby activating Ca 2+ -activated Cl -channels 1,4-10 . All these components of the signal transduction cascade are localized to sensory cilia, which are embedded in the mucus covering the MOE. These cilia provide a large interaction surface for odorants, and the cilia's small diameters facilitate large local increases in cytosolic cAMP and [Ca 2+ ].There has been broad consensus that Ca 2+ -activated Cl -channels powerfully amplify olfactory signal transduction 1,4-10 . These channels are thought to mediate an outward flow of Cl -, which generates a depolarizing current that, in rodents, is five-to tenfold larger than currents through CNG channels 8,11,12 . A prerequisite for Cl -efflux 3 is an inside-out electrochemical Cl --gradient. It is believed that cytosolic chloride concentration of OSNs is raised by the Na + K + 2Cl -co-transporter Nkcc1 9,10,13 and that [Cl -] is low in the mucus surrounding the cilia 14,15 . However, mucosal ion concentrations are difficult to measure in vivo, and Nkcc1 knockout mice display attenuated electro-olfactograms (EOGs) 11,16 , but normal olfactory sensitivity 17 .To investigate the role of Ca 2+ -activated Cl -channels in olfaction, we disrupted Ano2 in mice. Ano2 is a member of the Anoctamin (Tmem16) gene family, which encodes several Ca 2+ -activated Cl -channels [18][19][20] . Agreeing with recent results 13,21-23 , our knockout-controlled immunolabeling showed Ano2 expression in cilia of OSNs in the MOE, in microvilli of VNO sensory neurons and in synapses of photoreceptors. Additionally, we found Ano2 in the olfactory bulb. Ano1 expression overlapped with Ano2 in the VNO and the retina, but not in the MOE. Patch-clamp analysis showed that Ca 2+ -activated Cl -currents were undetectable in Ano2 -/-OSNs.Unexpectedly, however, EOGs of Ano2 -/-mice were reduced by only up to ~40%, and Ano2 -/-mice were able to smell normally. Our work calls for a revision of the current view that Ca 2+ -activated Cl -channels have a crucial role...

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Section: No Change Of Key Proteins and Axonal Convergencesupporting

confidence: 84%

Section: Discussionmentioning

confidence: 99%

Ca2+-activated Cl− currents are dispensable for olfaction

et al. 2011

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“…These experiments showed that up to 90% of the transduction current is carried by Cl − . A more precise characterization of the biophysical properties of olfactory CaCCs was achieved by experiments on excised inside-out membrane patches from the dendritic knob/cilia of mouse OSNs, a technique that allows a control of the concentration of Ca 2+ at the intracellular side of the channels (Reisert et al 2005;Pifferi et al 2006bPifferi et al , 2009b for CNG channels. Moreover, this conductance showed a Ca 2+ -dependent inactivation, which was reversible after removal of Ca 2+ for a few seconds, but also an irreversible run-down, indicating that some modulatory component of the channel may be lost after the excision of the membrane (Reisert et al 2003(Reisert et al , 2005.…”

Section: Calcium-activated Chloride Channels In the Cilia Of Olfactormentioning

confidence: 99%

Anoctamin 2/TMEM16B: a calcium‐activated chloride channel in olfactory transduction

Pifferi

Cenedese

Menini

2011

Experimental Physiology

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In vertebrate olfactory transduction, a Ca2+ -dependent Cl − efflux greatly amplifies the odorant response. The binding of odorants to receptors in the cilia of olfactory sensory neurons activates a transduction cascade that involves the opening of cyclic nucleotide-gated channels and the entry of Ca 2+ into the cilia. The Ca 2+ activates a Cl − current that, in the presence of a maintained elevated intracellular Cl − concentration, produces an efflux of Cl − ions and amplifies the depolarization. In this review, we summarize evidence supporting the hypothesis that anoctamin 2/TMEM16B is the main, or perhaps the only, constituent of the Ca 2+ -activated Cl − channels involved in olfactory transduction. Indeed, studies from several laboratories have shown that anoctamin 2/TMEM16B is expressed in the ciliary layer of the olfactory epithelium, that there are remarkable functional similarities between currents in olfactory sensory neurons and in HEK 293 cells transfected with anoctamin 2/TMEM16B, and that knockout mice for anoctamin 2/TMEM16B did not show any detectable Ca 2+ -activated Cl − current. Finally, we discuss the involvement of Ca 2+ -activated Cl − channels in the transduction process of vomeronasal sensory neurons and the physiological role of these channels in olfaction.

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“…Similar to the Ca 2+ -dependent Cl − conductance known to amplify transduction currents in canonical olfactory neurons (Pifferi et al 2009;Stephan et al 2009;Sagheddu et al 2010;Billig et al 2011;Dauner et al 2012;Ponissery-Saidu et al 2013;Henkel et al 2014), a considerable amount of stimulus-evoked VSN activity seems to be carried by a Ca…”

Section: Introductionmentioning

confidence: 97%

Elevated Cytosolic Cl⁻Concentrations in Dendritic Knobs of Mouse Vomeronasal Sensory Neurons

Untiet¹,

Moeller²,

Ibarra-Soria³

et al. 2016

CHEMSE

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In rodents, the vomeronasal system controls social and sexual behavior. However, several mechanistic aspects of sensory signaling in the vomeronasal organ remain unclear. Here, we investigate the biophysical basis of a recently proposed vomeronasal signal transduction component-a Ca 2+ -activated Cl − current. As the physiological role of such a current is a direct function of the Cl − equilibrium potential, we determined the intracellular Cl − concentration in dendritic knobs of vomeronasal neurons. Quantitative fluorescence lifetime imaging of a Cl − -sensitive dye at the apical surface of the intact vomeronasal neuroepithelium revealed increased cytosolic Cl − levels in dendritic knobs, a substantially lower Cl − concentration in vomeronasal sustentacular cells, and an apparent Cl − gradient in vomeronasal neurons along their dendritic apicobasal axis. Together, our data provide a biophysical basis for sensory signal amplification in vomeronasal neuron microvilli by opening Ca 2+ -activated Cl − channels.

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Calcium‐activated chloride currents in olfactory sensory neurons from mice lacking bestrophin‐2

Abstract: Olfactory sensory neurons use a chloride-based signal amplification mechanism to detect odorants.

Cited by 47 publications

References 55 publications

Ca2+-activated Cl− currents are dispensable for olfaction

Ca2+-activated Cl− currents are dispensable for olfaction

Anoctamin 2/TMEM16B: a calcium‐activated chloride channel in olfactory transduction

Elevated Cytosolic Cl⁻Concentrations in Dendritic Knobs of Mouse Vomeronasal Sensory Neurons

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Calcium‐activated chloride currents in olfactory sensory neurons from mice lacking bestrophin‐2

Abstract: Olfactory sensory neurons use a chloride-based signal amplification mechanism to detect odorants.

Cited by 47 publications

References 55 publications

Ca2+-activated Cl− currents are dispensable for olfaction

Ca2+-activated Cl− currents are dispensable for olfaction

Anoctamin 2/TMEM16B: a calcium‐activated chloride channel in olfactory transduction

Elevated Cytosolic Cl−Concentrations in Dendritic Knobs of Mouse Vomeronasal Sensory Neurons

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Elevated Cytosolic Cl⁻Concentrations in Dendritic Knobs of Mouse Vomeronasal Sensory Neurons