Abstract
The intracellular pH (pHi) 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 pHi by 0.50 +/- 0.09 unit (n = 4). Amiloride or Na(+)-free solution at the apical side had no effect on pHi. Cl- removal at the basolateral side led to an increase of pHi by 0.20 +/- 0.03 unit (n = 4) whereas apical removal had no influence on pHi. This effect was independent of Na+ and was insensitive to 0.2 mM 4,4'-diisothiocyanatodihydrostilbene-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.
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