Figure 5. Analysis of the falling phase of the suction pipette current using short cineole or IBMX stimulations.

Wild-type (A) or OMP^−/− (C) ORNs were exposed to cineole and the falling phases of the suction pipette current fitted with single exponentials (grey line) with time constants of 26 and 260 ms, respectively. To minimize the contribution of the Ca²⁺-activated Cl⁻ conductance external Ca²⁺ was reduced to 20 μm (low Ca²⁺) for an OMP^+/+ (B) and an OMP^−/− (D) ORN. The fitted exponentials had time constants of 46 and 570 ms. Stimulation durations were chosen to generate peak currents of comparable magnitudes and were 40, 25, 50 and 25 ms in A–D, respectively, and chosen to elicit small currents, typically between 5 and 20 pA. Recordings in A and B are from the same OMP^+/+ ORN, and in C and D are from the same OMP^−/− ORN. Exposure to 1 mm IBMX for 50 ms in normal Ringer solution generated suction pipette currents with comparable time courses in wild-type (E) or OMP^−/− (G) neurons (time constants of 25 and 39 ms). In low Ca²⁺ Ringer solution the kinetics of the falling phase also did not change much and could be fitted with time constants of 40 ms in the wild-type (F) and 53 ms in the OMP^−/− ORN (G). Traces are in most cases averages of 5 recordings. Recordings in E–H are from different ORNs. Odourant or IBMX stimulations commenced at 40 ms.