A linear 16 pS Cl- channel in the apical membrane of Caco-2 cells

A linear Cl- channel with a mean conductance of 16.3 +/- 0.4 pS (n = 7), as determined for inwardly directed currents in the cell-attached mode, was identified by the patch clamp technique in the apical membrane of Caco-2 cells in the early stage of postconfluential differentiation. This channel exhibited a low spontaneous activity (in 3 out of 137 experiments) and was not activated by strong polarization of the holding potential. After stimulation of the cAMP signal transduction cascade at different levels the 16 pS Cl- channel was activated in 7 out of 67 experiments during continuous cell-attached recording and remained active after excision of the patch. This channel differed markedly from both a linear low conductance Cl- channel and an intermediate conductance, outwardly rectifying (ICOR) Cl- channel, already reported for Caco-2 and other colonic cell lines. Thus the 16 pS channel may represent a further type of apical Cl- channel in colonocytes.