Cl- secretion in epithelial monolayers of mucus-forming human colon cells (HT-29/B6).

HT-29, an undifferentiated human colon cell line, is known to differentiate when cultured without glucose. This study aimed to characterize ion transport in the clone HT-29/B6, which was selected from HT-29 cells differentiated by glucose-free culture. HT-29/B6 cells seeded onto filter membranes grew as polarized monolayers, mainly consisting of mucus-forming cells and exhibiting high transepithelial resistance. Short-circuit current (Isc) of unstimulated HT-29/B6 monolayers in Ussing chambers was 0.1 +/- 0.01 mumol.h-1.cm-2, and conductance was 2.0 +/- 0.2 mS/cm2. Serosal forskolin (FSK; 10(-5) M) induced a sustained Isc of 1.9 +/- 0.1 mumol.h-1.cm-2, associated with a rise of intracellular adenosine 3',5'-cyclic monophosphate (cAMP). Isc was identified as Cl- secretion by tracer studies and by the inhibitory effects of serosal bumetanide and Ba2+. The Cl- channel blockers NPPB and DPC diminished FSK-induced Isc at respective doses of 3 x 10(-4) and 10(-3) M, being effective from either side of the monolayer. Cl- secretion could be triggered by vasoactive intestinal peptide (10(-8) M), prostaglandin E1 (10(-6) M), and dibutyryl cAMP (10(-3) M) as well. In conclusion, HT-29/B6 cells grow as polarized monolayers, forming mucus and secreting Cl- in response to secretagogues. This clone may not only serve as a model for investigation of cellular mechanisms of intestinal Cl- secretion but may also be helpful to elucidate the contribution of mucus cells to this process.