Cell-to-cell diffusion of fluorescent dyes in paired ventricular cells

The intracellular and cell-to-cell diffusion of fluorescent dyes of various molecular sizes were studied in enzymatically isolated paired ventricular cells of the guinea pig heart. Fluorescein sodium (mol wt 332), 6-carboxyfluorescein (mol wt 376), Lucifer yellow CH (mol wt 457), lissamine rhodamine B-200 (mol wt 559), and tetraglycine-conjugated lissamine rhodamine B-200 (mol wt 859) were all diffused into the single ventricular cell through the patch-clamp pipette. All these dyes were able to diffuse through the gap junction of the paired cells. The diffusion coefficient of 6-carboxyfluorescein in the cytoplasm was 5.8 X 10(-6) cm2/s, Lucifer yellow CH was 3.0 X 10(-6) cm2/s, and lissamine rhodamine B-200 was 8.6 X 10(-7) cm2/s. Permeability of the gap-junctional membrane was 6.8 X 10(-4) cm/s for 6-carboxyfluorescein, 2.8 X 10(-4) cm/s for Lucifer yellow CH and 7.4 X 10(-5) cm/s for lissamine rhodamine B-200. Thus lissamine rhodamine B-200 diffused in the cytoplasm and through the gap junction approximately 10 times slower than 6-carboxyfluorescein. Tetraglycine-conjugated lissamine rhodamine B-200 (mol wt 859) passed through the gap junction, suggesting that the critical pore size of the ventricular gap junction may be somewhat larger than that of the conjugated tetraglycine rhodamine.