Chloride conductance in HT29 cells: investigations with apical membrane vesicles and RT-PCR.

Vesicles enriched in a marker enzyme for apical membranes were isolated from HT29 cells. These vesicles contain an anion conductance with the selectivity gluconate approximately sulphate<F-<Cl-<Br-<NO3-<I-<SCN-. K+ diffusion potential-driven 36Cl- uptake was inhibited by 5-nitro-2-(3-phenylpropylamino)benzoate (NPPB)>4, 4'-diisothiocyanatostilbene-2,2'-disulphonate (DIDS)>glibenclamide. The Cl- conductance was insensitive to Ca2+ and to extravesicular cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP) and inosine 5'-triphosphate (ITP). Using the reverse transcription polymerase chain reaction (RT-PCR) technique and sequencing of the amplified products we detected messenger ribonucleic acid (mRNA) for the cystic fibrosis transmembrane conductance regulator (CFTR), the putative Cl- channel or Cl- channel regulator pICln, and the Cl- channels ClC-2, ClC-3, ClC-5 and ClC-6 in HT29 cells. The properties of the vesicles' Cl- conductance resemble those of the intermediate conductance outwardly rectifying Cl- channel and tentatively exclude contributions of CFTR, pICln and ClC-2. Whether ClC-3, ClC-5, ClC-6 are involved in Cl- conductance remains to be determined.