Figure 3.

The diffusion coefficient of single IP₃R in intact living cells estimated by tracking SCCaFT positions during successive channel openings. (a, Inset) Mean locations ±1 SE determined from eight sequential events arising at a single isolated site throughout a 10 s recording. The graph plots the mean-square displacement from origin of these locations as a function of time. (Line) Linear regression fit to the data. The slope of the line corresponds to a two-dimensional diffusion coefficient of 0.006 μm² s⁻¹. (b, Inset) Diffusion coefficients estimated from 15 separate records (solid circles) as in panel a. Data points plotted as zero correspond to negative regression slopes of displacement squared versus time. The square symbol shows the mean and standard error of the diffusion coefficient estimated for all 15 channels. Plot illustrating the mean displacement that would be reached after different times for each of the individual channels in panel b (inset), together with that of a channel diffusing with the mean diffusion coefficient of 0.003 μm² s⁻¹ (square symbol).