Figure 1.

Gating of CFTR Cl⁻ channels. (A and B) Real (A) and schematic (B) current traces are shown to depict the four kinetic states of CFTR; closed (C), blocked (C_B), an open state susceptible to Mops block (O1), and an open state less susceptible to Mops block (O2). Openings adjacent to the channel closed state (C), the first and last openings, were identified as the O1 or O2 state on the basis of their duration. (C) Closed duration histograms. Closures were identified as C or C_B by using a delimiter of 79 ms (arrow). Dashed lines indicate time constants as determined by a least-square fit to the sum of two exponentials. Inset shows long-duration event with expanded axes. (D) Duration histograms of first openings. Data were fit by two exponentials (dashed lines). The short openings (τ = 0.86 ms) represent O1, and the longer openings (τ = 34.88 ms) represent O2. The nadir (5.75 ms; arrow) delineated the two distributions. (E) Duration histograms of last openings. Two exponentials (dashed lines) identify O1 openings (τ = 0.86 ms) and O2 openings (τ = 33.30 ms). Arrow indicates the nadir (2.04 ms). Data are representative examples from experiment no. 1006.