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Published on: October 29, 2011
Single Ca(2+)-activated Cl(-) channel currents recorded from toad olfactory cilia
Ricardo Delgado1, Casilda V Mura1, Juan Bacigalupo2
1Department of Biology, Faculty of Sciences, University of Chile, 7800024, Ñuñoa, Santiago, Chile.
Background:
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.
Results:
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.
Conclusions:
These results are consistent with a novel olfactory cilia channel, which might play a role in odor transduction.
Insights
Researchers identified novel calcium-activated chloride channels in toad olfactory cilia, suggesting a new role in odor transduction beyond known channels like ANO2. These findings advance our understanding of olfactory sensory neuron function.
Area of Science:
- Olfactory neuroscience
- Ion channel physiology
- Chemosensation
Background:
- Odor transduction involves cyclic adenosine monophosphate (cAMP) signaling and cyclic nucleotide-gated (CNG) channels in olfactory sensory neurons.
- Calcium influx through CNG channels activates chloride channels, enhancing neuronal depolarization.
- Anoctamin 2 (ANO2) is a primary calcium-activated chloride channel in olfaction, but its absence in knockout mice only partially affects olfactory responses, suggesting other channels are involved.
Purpose of the Study:
- To investigate the presence and function of calcium-activated chloride channels in toad olfactory cilia.
- To identify potential novel channels involved in olfactory transduction beyond ANO2.
Main Methods:
- Recording of unitary chloride currents from inside-out membrane patches excised from individual toad olfactory cilia.
- Characterization of channel conductance and calcium dependence.
- Immunoreactivity analysis using antibodies against ClCa and ANO2 channels.
Main Results:
- Detection of unitary chloride currents with significant calcium dependence in toad olfactory cilia.
- Identified conductances of 12 and 24 pS, which are higher than previously reported channels.
- Observed approximately fivefold higher calcium affinity (K0.5 = 0.38 µM) compared to other channels.
- Found immunoreactivity for both anti-ClCa and anti-ANO2 antibodies in olfactory cilia.
Conclusions:
- The findings suggest the presence of a novel olfactory cilia channel with a significant role in odor transduction.
- The results are consistent with a cooperative function of ClCa and ANO2 channels in olfactory chemotransduction.
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