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1 Millennium Institute for Advanced Studies in Cell Biology and Biotechnology, Santiago, Chile
2 Institute of Biomedical Sciences, Faculty of Medicine, University of Chile, Santiago, Chile
3 Millennium Institute for Advanced Studies in Cell Biology and Biotechnology, Santiago, Chile; Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile
* To whom correspondence should be addressed. E-mail: bacigalu{at}uchile.cl.
Olfactory receptor neurons (ORNs) respond to odorants with changes in the action potential firing rate. Excitatory responses, consisting on firing increases, are mediated by a cyclic AMP cascade that leads to the activation of cationic non-selective cyclic nucleotide-gated (CNG) channels and Ca2+-dependent Cl- (ClCa) channels. This process takes place in the olfactory cilia, where all protein components of this cascade are confined. ORNs from various vertebrate species have also been shown to generate inhibitory odor responses, expressed as decreases in action potential discharges. Odor-inhibition appears to rely on Ca2+-dependent K+ (KCa) channels, but the underlying transduction mechanism remains unknown. If these channels are involved in odor-transduction, they are expected to be present in the olfactory cilia. We found that a specific antibody against a large conductance KCa recognized a protein of 116~ kDa in Western blots of purified rat olfactory ciliary membranes. Moreover, the antibody labeled ORN cilia in in isolated ORNs from rat and toad (Caudiverbera caudiverbera). In addition, single-channel recordings from inside-out membrane patches excised from toad chemosensory cilia showed the presence of four different types of KCa channels, with unitary conductances of 210, 60, 12 and 29 and 60 pS, high K+-selectivity and Ca2+ sensitivities in the low micromolar range. Our work demonstrates the presence of K+ channels in the ORN cilia and supports their participation in odor transduction.
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