Figure 7.

BK channels typically gate in a minimum of two to three open and three to five closed states in 0 Ca²⁺ _i, inconsistent with gating mechanisms based on the Monod-Wyman-Changeux model with Ca²⁺ _i as the allosteric activator, which predicts gating in one open and one closed state in 0 Ca²⁺ _i. The minimal number of significant exponential components required to describe the open and closed dwell-time distributions in 0 Ca²⁺ _i are plotted against the numbers of analyzed intervals. Data for α channels (open symbols) are from 34 sets of data from eight different patches. Data for α+β₁ channels (filled symbols) are from 52 sets of data from 12 patches. A number of data sets, each at a different membrane potential, were typically obtained from each patch. Each symbol type plots estimates obtained from a single patch. Data from patches containing multiple channels were included when the channel activity was so low that channel openings did not occur simultaneously. When the analysis was restricted to the 27 data sets from the seven patches containing a single channel, the same results were obtained, except that only two, rather than three, open states were detected for α channels. There was no obvious effect of voltage on the number of detected states.