Fig. 1.

Steady-state solute penetrance of t-tubules in rabbit and mouse ventricular cardiomyocytes. (A) Fluorescence images of rabbit (Left) and mouse (Right) cardiomyocytes bathed in a 10-kDa rhodamine B-linked dextran reference dye (Top) and 4- or 70-kDa fluorescein-linked dextran test dyes (Middle). Cells were incubated for >10 min to reach steady state. The test-to-reference ratio (F_T/F_R) images are shown (Bottom) (color table at the right). (Scale bar for all panels: 5 μm.) (B) Stokes radii of the test solutes, as measured with FCS, and compared with MW^1/3. Error bars for three to six determinations were generally smaller than the symbol size. Open symbols indicate dextran-based probes. (C) Dependence of F_T/F_R from rabbit (red circles) and mouse (blue crosses) on the measured Stokes radius. Numbers of independent determinations are indicated beside each data point.