PH, MORPHOLOGY, AND DIFFUSION IN LATERAL INTERCELLULAR SPACES OF EPITHELIAL-CELL MONOLAYERS

The lateral intercellular spaces (LIS) of reabsorptive epithelia are t he site ofthe proposed local osmotic gradient responsible for transepi thelial transport. We developed techniques for loading the LIS of livi ng cultured renal cells (MDCK and LLC-PK1) with the fluorescent dye 2' ,7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF), visualizing LIS geometry, measuring pH, and determining the BCECF diffusion coefficie nt within the LIS. The LIS pH was remarkably constant and differed sub stantially from that of the superfusate in both the presence and absen ce of HCO3 or CO2. The LIS of MDCK cells had a pH of 7.66 +/- 0.04 in bicarbonate-free solutions of pH 7.0, 7.4, or 7.8. In bicarbonate-cont aining solutions, MDCK LTS pH was acidic to the superfusate by 0.3-0.4 units. In the absence of bicarbonate, the LIS of LLC-PK1 cells was ma rkedly acidic (6.83 +/- 0.05), becoming alkaline by similar to 0.25 un its in the presence of bicarbonate. Gradients in pH or dye concentrati on were not detected within the LIS. The diffusion coefficient of BCEC F within the LIS was approximately equal to that seen in free solution .