BASOLATERAL MECHANISMS OF INTRACELLULAR PH REGULATION IN THE COLONIC EPITHELIAL-CELL LINE HT29 CLONE 19A

The intracellular pH (pH(i)) of the colonic tumour cell line HT29 cl.19A was studied by microspectrofluorometry using the pH-sensitive dye BCECF. Single cells within a confluent monolayer, grown in a polarized manner on permeable supports, were examined. An amiloride-sensitive Na+/H+ exchange and a stilbene-insensitive Cl-/HCO3- exchange mechanism have been identified in the basolateral membrane. Removal of Na from the basolateral solution caused a decrease of pH(i) by 0.50 +/- 0.09 unit (n = 4). Amiloride or Na+-free solution at the apical side had no effect on pH(i). Cl- removal at the basolateral side led to an increase of pH(i) by 0.20 +/- 0.03 unit (n = 4) whereas apical removal had no influence on pH(i). This effect was independent of Na+ and was insensitive to 0.2 mM 4,4'-diisothiocyanato-dihydrostilbene-2,2'-disulphonic acid. A basolateral Cl-/ HCO3- exchanger is the most likely explanation for this observation. The Na+/H+ exchange mechanism in the basolateral membrane is an acid extruder, whereas the Cl-/HCO3- exchanger is an acid loader. Both of these mechanisms are important for the maintenance of intracellular pH in HT29 cl.19A cells.