Nicotine in the ER of neurons. (A–D) Exemplar nicotine-induced fluorescence increases for cultured hippocampal neurons transduced with AAV2/1.sin1.iNicSnFR3b_PM (A and B) or with AAV2.sin1.iNicSnFR3b_ER (C and D). (A and C) 20-s nicotine pulses, followed by 20-s wash in HBSS. The average waveform for five cells at each [nicotine] is overlaid for the PM and ER traces in A and C, respectively. The SEM is shown as colored bands around each line. Dose–response relations are shown in B and D. (E and F) Human dopaminergic neurons transfected with iNicSnFR_ER3a. (E) Typical nicotine-induced fluorescence during 20-s pulses of nicotine at the indicated concentrations. Data were subjected to a triangle filter (half-time, 1 s). (F) Full dose–response data from 20 transfected human dopaminergic neurons. Inset, start of the dose relation at [nicotine] ≤ 5 µM. The slope of the line, [ΔF/F₀]/[nicotine], is 0.087 µM⁻¹.