Determination of V(r) for confined diffusion of CFTR. (A) Particle positions and corresponding d(r)/d(0) for four CFTR molecules. Solid lines represent best fits to the distribution function for a spring potential. (B) Mean d(r)/d(0) from 65 trajectories of individual CFTR molecules. Best fits to distribution functions for indicated potentials are shown. For the spring potential, k = 2.6 ± 0.8 pN/μm. (C) Histograms of distribution coefficient k, confinement radius rc, and diffusion coefficient D1–3. (D) Particle positions and corresponding d(r)/d(0), as in A, for CFTR after treatment of cells with a low concentration of latrunculin. (E) Mean d(r)/d(0) and best fits to spring potential shown for control cells (same data as in panel B), and cells treated with jasplakinolide (k = 2.4 ± 0.8 pN/μm, 42 trajectories) or latrunculin (k = 1.9 ± 0.6 pN/μm, 27 trajectories). (F) MSD plot for control versus latrunculin-treated cells.