Comparison of diffusion restrictions in skeletal muscle, murine cardiac myofilaments, and intact murine cardiac myocytes, plotted in dependence on hydrated radius. (A–C) Results are fitted to Boltzmann equations, the slope of which is threefold steeper for intact cardiac myocytes (C) than for intact skeletal muscle (A) or isolated cardiac myocytes (B). (A) Filled circles give the ratio of free diffusion coefficients in skeletal muscle versus free water. The data are replotted from Blatter and Wier (1990), with the left six data points corresponding to sorbitol, sucrose, and ATP (Kushmerick and Podolsky, 1969), as well as soluble tetramethylmurexide derivatives (Hirota et al., 1989), followed by the additional absorbance dyes, arsenazo III, and antipyrylazo II (Maylie et al., 1987a, 1987c, 1987b). The open squares below the skeletal muscle data points correspond to Indo-1 and Fura-2 diffusion in guinea pig myocytes from the Blatter/Wier study. (B) Ratio of pipette tip conductance with and without aspirated cardiac myofilaments for eight ion pairs. Hydrated radii are the average of the anion and cation employed. (C) Ratio of best estimates of diffusion coefficients for selected solutes in murine BL6 myocytes versus free water. SR, sulforhodamine; CF, carboxyfluorescein.