Fits of Scheme 1 to α2 single-channel data. (A) Scheme 1 (Mangin et al., 2003) contains two binding sites and a single open state linked to the fully liganded shut state. Directly connected to the bound shut states are short-lived desensitized states. Entry into these states is independent of glycine concentration. (B) The results of simultaneous fit of a dataset (containing four single-channel patches) with Scheme 1. The fit was performed with the assumption of interacting binding sites. The histograms are the experimental open-period and shut-time distributions, the continuous curves are the calculated distributions predicted from the model and fitted rate constants (resolution, 20 µs), and the dashed lines are the predicted fits at perfect resolution (i.e., when no events are missed). (C) Simulation of a single-channel record (at 20 µM glycine) using the fitted rate constants of one of the sets fitted with Scheme 1. This fit failed to predict the long shut times between groups of openings we observed in the experimental records, but it instead predicted that at low concentration we should observe frequent bursts. (D) Similar to C, using a different dataset (same set as in B), fitted with Scheme 1. Although this set can predict long gaps and clusters of openings, it also predicts very short bursts with lower Popen that are not observed at any of our single-channel records (compare with Fig. 2 A).
