Single Ca(2+)-activated Cl(-) channel currents recorded from toad olfactory cilia.
Odor transduction, occurring in the chemosensory cilia of vertebrate olfactory sensory neurons, is triggered by guanosine triphosphate-coupled odor receptors and mediated by a cyclic adenosine monophosphate (cAMP) signaling cascade, where cAMP opens cationic non-selective cyclic nucleotide-gated (CNG) channels. Calcium enters through CNG gates Ca(2+)-activated Cl(-) channels, allowing a Cl(-) inward current that enhances the depolarization initiated by the CNG-dependent inward current. The anoctamin channel 2, ANO2, is considered the main Ca(2+)-activated Cl(-) channel of olfactory transduction. Although Ca(2+)-activated Cl(-) channel-dependent currents in olfactory sensory neurons were reported to be suppressed in ANO2-knockout mice, field potentials from their olfactory epithelium were only modestly diminished and their smell-dependent behavior was unaffected, suggesting the participation of additional Ca(2+)-activated Cl(-) channel types. The Bestrophin channel 2, Best2, was also detected in mouse olfactory cilia and ClCa4l, belonging to the ClCa family of Ca(2+)-activated Cl(-) channels, were found in rat cilia. Best2 knock-out mice present no electrophysiological or behavioral impairment, while the ClCa channels have not been functionally studied; therefore, the overall participation of all these channels in olfactory transduction remains unresolved.



We explored the presence of detectable Ca(2+)-activated Cl(-) channels in toad olfactory cilia by recording from inside-out membrane patches excised from individual cilia and detected unitary Cl(-) current events with a pronounced Ca(2+) dependence, corresponding to 12 and 24 pS conductances, over tenfold higher than the aforementioned channels, and a approx. fivefold higher Ca(2+) affinity (K0.5 = 0.38 µM). Remarkably, we observed immunoreactivity to anti-ClCa and anti-ANO2 antibodies in the olfactory cilia, suggesting a possible cooperative function of both channel type in chemotransduction.



These results are consistent with a novel olfactory cilia channel, which might play a role in odor transduction.
Department of Biology, Faculty of Sciences, University of Chile, 7800024, Ñuñoa, Santiago, Chile.
Ricardo
R
Delgado
Department of Biology, Faculty of Sciences, University of Chile, 7800024, Ñuñoa, Santiago, Chile.
Casilda V
CV
Mura
Department of Biology, Faculty of Sciences, University of Chile, 7800024, Ñuñoa, Santiago, Chile. bacigalu@uchile.cl.
Juan
J
Bacigalupo
D029845:Amphibian Proteins / Q000378:metabolism*; D000818:Animals; D001001:Anura; D002118:Calcium / Q000378:metabolism; D002413:Cations, Divalent / Q000378:metabolism; D018118:Chloride Channels / Q000378:metabolism*; D002923:Cilia / Q000378:metabolism; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D009831:Olfactory Mucosa / Q000378:metabolism; D018034:Olfactory Receptor Neurons / Q000378:metabolism*; D018408:Patch-Clamp Techniques
D029845:Amphibian Proteins; D002413:Cations, Divalent; D018118:Chloride Channels; D054815:Cyclic Nucleotide-Gated Cation Channels; D002118:Calcium
Anoctamin-2; Bestrophin-2; Calcium; ClCa4l; Ion channel; Odor transduction; Olfactory cilia; Olfactory sensory neuron