ANO2 is the cilial calcium-activated chloride channel that may mediate olfactory amplification

Stephan, Aaron B.; Shum, Eleen Y.; Hirsh, Sarah; Cygnar, Katherine D.; Reisert, Johannes; Zhao, Haiqing

doi:10.1073/pnas.0903304106

Cited by 305 publications

(426 citation statements)

References 37 publications

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“…Our N-terminal antibody did not detect a truncated protein in Ano2 -/-tissue, suggesting the occurrence of nonsensemediated mRNA decay, instability of the truncated protein, or both. Ano2 -/-mice were born at Mendelian ratio; they grew, mated, and survived normally and lacked an immediately apparent phenotype.Consistent with previous data [21][22][23] , western blots indicated that Ano2 is most highly expressed in olfactory epithelium (MOE and VNO) and eye tissue (Fig. 1a,b).…”

supporting

confidence: 92%

“…5d,f), but not at 13 µM free Ca 2+ (Fig. 5g,i) similar to data reported for Ca 2+ -activated Cl -currents for heterologously expressed Ano1 and Ano2 [20][21][22]33,34 and for frog OSNs 7 . We could not detect these Cl -currents in Ano2 -/-OSNs (Fig.…”

supporting

confidence: 87%

“…The superfusate could be switched to a solution containing niflumic acid (NFA). NFA has been widely used to block Ca 2+ -activated Cl -channels in OSNs and other 6 cells 4,6,9,11,16,34,36,37 and inhibits both Ano1 and Ano2 18,20,21,33,34 . The response to odorants was reduced by roughly 40% in Ano2 -/-EOGs compared to the wild type (Fig.…”

Section: Disruption Of Ano2 Moderately Reduces Eogsmentioning

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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supporting

confidence: 92%

supporting

confidence: 87%

Section: Disruption Of Ano2 Moderately Reduces Eogsmentioning

confidence: 99%

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Ca2+-activated Cl− currents are dispensable for olfaction

et al. 2011

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“…2008) and ANO2 (TMEM16B) (Stephan et al . 2009; Stohr et al . 2009) subunits identified as bona fide CaCCs (see Pedemonte & Galietta, 2014 for review).…”

Section: Introductionmentioning

confidence: 99%

“…In addition, ANO2 has been identified as a CaCC subunit in the cilia of olfactory sensory neurons (Stephan et al . 2009; Billig et al . 2011).…”

Section: Introductionmentioning

confidence: 99%

Activation of Ca²⁺‐activated Cl⁻ channel ANO1 by localized Ca²⁺ signals

Jin

Shah

et al. 2014

The Journal of Physiology

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Ca2+‐activated chloride channels (CaCCs) regulate numerous physiological processes including epithelial transport, smooth muscle contraction and sensory processing. Anoctamin‐1 (ANO1, TMEM16A) is a principal CaCC subunit in many cell types, yet our understanding of the mechanisms of ANO1 activation and regulation are only beginning to emerge. Ca2+ sensitivity of ANO1 is rather low and at negative membrane potentials the channel requires several micromoles of intracellular Ca2+ for activation. However, global Ca2+ levels in cells rarely reach such levels and, therefore, there must be mechanisms that focus intracellular Ca2+ transients towards the ANO1 channels. Recent findings indeed indicate that ANO1 channels often co‐localize with sources of intracellular Ca2+ signals. Interestingly, it appears that in many cell types ANO1 is particularly tightly coupled to the Ca2+ release sites of the intracellular Ca2+ stores. Such preferential coupling may represent a general mechanism of ANO1 activation in native tissues.

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