Figure 5. Effect of modification on βS518C single-channel kinetics.

A, changes in single-channel open probability (P_o) due to modification by MTSET or MTSEA. P_o before and after modification by MTSEA (left panel) and MTSET (right panel). P_o was determined during the minute prior to and after, modification, respectively. The P_o data are from patches that contained single active channels. Holding potential was −100 mV. Filled symbols represent individual experiments. B, open and closed time distributions of βS518C channels before and after modification. Time distributions were obtained from single-channel excised outside-out patches at −100 mV. The time constants and the relative weights of the components are listed in Table 1. The overall P_o of the data used for the kinetic analysis was 0.52 (unmodified), 0.95 (MTSEA-modified) and 0.97 (MTSET-modified). The number of exponential components of the fit was determined according to Colquhoun & Sigworth (1995) by visual inspection of the histograms and by the criterion of whether a given number of components was required to fit histograms derived from individual experiments. Therefore, open times of unmodified and MTSET-modified channels were fitted with two components. The open time distribution of MTSEA-modified channels was then fitted with two components to be better able to compare these data with those obtained in the other two conditions. Closed times were fitted with two exponential components.