Sequential activation of the olfactory CNG and Cl⁻ transduction channels. (A) Receptor currents from a mouse ORN recorded using the whole cell patch-clamp technique. The ORN was loaded with the photolysable compound caged 8-Br-cAMP via the recording pipette. Exposure to a short UV flash (arrow) caused the release of the “cage” from 8-Br-cAMP, which triggered the opening of the CNG channel and a small initial Na⁺ and Ca²⁺ current. After a clear delay (in this particular ORN), an additional current was generated that could be blocked by the Ca²⁺-activated Cl⁻ channel blocker, niflumic acid. (B) Same data as in A but on an expanded time scale to show the pronounced sequential activation of the two currents. Modified from Boccaccio and Menini (2007) with permission from the authors and the American Physiological Society.