Figure 3.

The effective desensitization rate as a function of the number of bound ACh molecules. Each symbol is a patch. For each patch, an occupancy probability in unliganded, monoliganded, and diliganded states was calculated from the ACh concentration, the equilibrium dissociation constant (100 μM in 115 mM NaCl and 160 μM in 142 mM KCl), and the gating equilibrium constant according to Model I (see methods). The desensitization rate constant for un- and diliganded AChR was estimated by linear extrapolation to unity occupancy. Diliganded AChR (open plus closed) desensitize at 3.7 s⁻¹ while unliganded AChR desensitize much more slowly, at <0.1 s⁻¹.