Figure 4.
Multiregime behavior in the presence of CaVβ2b subunits. Symbols show distribution of open probabilities and durations of resolved clusters (left Y axis). (Solid lines) Cumulative distribution of cluster open probabilities (right Y axis). (Dashed lines) Cumulative normal distributions with means and variances obtained from the statistics of cluster's open-probability values, weighted by the durations of the clusters. In the case of CaVβ1a, a good agreement between the experimental and the theoretical normal open-probability distributions is seen. By contrast, in the case of CaVβ2b, the predicted normal distribution is much narrower than the observed open-probability distribution, indicating that channels switch between high- and low-open-probability regimes. The threshold to separate high-open-probability (CaVβ2b-like) from low-open-probability (CaVβ1a-like) regimes was set at open probability = 0.0037 (vertical shaded lines), which is equal to the mean + SD of the open-probability distribution from CaVβ1a experiments.