ACIDIC PH OF THE LATERAL INTERCELLULAR SPACES OF MDCK CELLS CULTURED ON PERMEABLE SUPPORTS

The pH of the lateral intercellular space (LIS) of Madin-Darby canine kidney (MDCK) cell monolayers grown on permeable supports was investig ated by microspectrofluorimetry using BCECF (2',7'-bis(carboxyethyl)-5 ,6-carboxyfluorescein). The permeability of the support was selectivel y reduced by growing ZnAl-silicate crystals inside its pores. The diff usion of BCECF across the filter was sufficiently retarded to allow me asurements of fluorescence in the LIS. The LIS pH and intracellular pH of the cells surrounding them were determined in HEPES-buffered solut ions. When the perfusate pH was 7.4, the LIS pH was more acidic (7.06 +/- 0.02) and equaled the cytoplasmic pH (7.08 +/- 0.05). When perfusa te was changed to pH 7.0 or 7.8, the LIS changed linearly by about hal f the magnitude of the perfusate pH. Intracellular pH followed LIS pH variations between perfusate pH 7.0 and 7.4 but was significantly high er when perfusate pH was 7.8. Tight junctional H+ permeability was und etectably low. The low steady-state pH in the LIS was not altered by i nhibitors of acid transport or low temperature. Rapid perturbations of pH in the LIS showed that protons were not immobilized in the LIS, Th e acidic microenvironment within the LIS may be the result of bufferin g by the cell surface proteins.