Figure 1. The effect of acetylcholine-induced desensitization on the amplitude of the fast fluorescence component. (A) Fluorescence traces obtained when nAcChoR membranes are preincubated with 3 [micro sign]M acetylcholine (final concentrations after mixing) for the indicated times and then rapidly mixed with 5 mM acetylcholine and 10 [micro sign]M Dns-C6-Cho(final concentrations). The amplitude of the fast fluorescent component was 0.341, 0.197, and 0.064 (arbitrary units) upon preincubation for 15 ms, 2 s, and 60 s, respectively. (B) The amplitude of the fast fluorescent component as a function of preincubation time is plotted using preincubating acetylcholine concentrations of either 3 [micro sign]M or 1 mM. The curves are fits of the data to an exponential Equation toderive the apparent rates of acetylcholine-induced desensitization. Acetylcholine at concentrations of 3 [micro sign]M and 1 mM induced desensitization with apparent rates of 0.34 +/- 0.02 s-1and 2.2 +/- 0.3 s-1, respectively.