The influence of high K solution on the longitudinal movement of Lucifer Yellow CH along dog atrial trabeculae was investigated. It was found that in normal heart muscle the dye diffused from cell-to-cell and the average diffusion coefficient (D) was 4.3 +/- 1.3 X 10(-7) cm2/s. In muscles exposed to 20, 40 or 60 mM K solution the resting potential was reduced from -78 mV (S.E. +/- 0.71) (control) to -41 mV (S.E. +/- 0.95), -30 mV (S.E. +/- 0.64) and -22.5 mV (S.E. +/- 0.64), respectively. Despite the maintained depolarization the cell-to-cell diffusion of Lucifer Yellow CH did not change. These findings indicate that the junctional permeability in heart muscle is not influenced by the non-junctional membrane potential.