Fig. 6.

Time course of recovery from nicotine-induced desensitization is subunit-dependent. A, Histogram of the mean time constants for a single exponential fit to the time course of recovery from desensitization induced by 1 μm nicotine for a number of nAChR subtypes. Data from experiments in calcium-free and calcium-containing media were combined. The numberof experiments for each subtype is indicated inparentheses. Recovery was estimated after nicotine incubation of 15–20 min (α3β2 andα4β2 receptors) and 60 min (α3β4and α4β4 receptors). B, Plot of normalized peak current amplitudes (o—o) induced by a repetitively applied ACh test pulse (5 μm; 5 min intervals) with respect to time before, during (open bar), and after continuous perfusion with 300 nm nicotine in calcium-containing media for an oocyte expressing α4β4 receptors.C, Plot of normalized peak amplitudes of currents (o—o) induced by a repetitively applied ACh test pulse (100 μm; 10 min intervals) with respect to time before, during (open bar), and after continuous perfusion with 3 μmnicotine in calcium-free media for an oocyte expressing α3β2 receptors. The time constants (τ) in B andC result from single exponential fits (solid line) to the time course of recovery from desensitization. The exponential fit assumed recovery to control values.