Ca 2+ -activated Cl current predominates in threshold response of mouse olfactory receptor neurons

Significance Odorants activate in mammalian olfactory receptor neurons (ORNs) an inward cyclic nucleotide-gated (CNG), nonselective cation current and, importantly, a follower inward Ca2+ -activated Cl current serving to amplify the olfactory signal. This concept is nonetheless refuted by a report describing no increase in behavioral olfactory threshold for a mouse line engineered to harbor an ablated gene for the Cl current. Two other reports on the same mouse line, however, did observe some subtle olfactory defects. We take a different approach here by dissecting the normal mouse ORN receptor current into its CNG- and Cl-current components, and showing that, at signaling threshold to the brain, the Cl current indeed accounts for most of the olfactory response, and thus should contribute importantly to olfactory signaling.