Fast response termination of the receptor current is required for reliable AP generation during repetitive stimulation. (A) Suction pipette recording from an isolated wild-type ORN. The ORN was exposed twice with an interpulse time of 0.25 s to the PDE inhibitor IBMX (see solution monitor at top). This led to an increase in ciliary cAMP and generation of the transduction current. APs were fired during the rising phases of both responses, as indicated by the AP raster plot above the current trace. The inset shows the rapid decline of the AP amplitude during the response. (B) The deletion of the CaM-binding site on the B1 subunit of the CNG channel (CNGB1^ΔCaM) causes a subtle response prolongation, which reduces the possibility of APs being generated in response to the second IBMX exposure after a 0.25-s interpulse time. (C and D) The same ORNs as in A and B, respectively, but with the longer interpulse time of 0.5 s. Now both wild-type and CNGB1^ΔCaM ORN generate APs in response to the second stimulation. (E) Percentage of ORNs that fire APs in response to the second stimulation, dependent on the interpulse period. Data points are mean ± 95% confidence interval (n = 19–49 ORNs; *, χ² test; P = 0.007). Modified from Song et al. (2008) with permission from Elsevier.