Small-conductance chloride channels induced by cAMP, Ca2+, and hypotonicity in HT29 cells: ion selectivity,...

Previous studies in HT29 cells utilizing the cell-attached nystatin (CAN) method [Greger R, Kunzelmann K (1991) Pflügers Arch 419:209-211] have revealed that the Cl- channels induced by cAMP or by increasing cytosolic Ca2+, e.g. by addition of ATP, and by hypotonic cell swelling share in common their conductance, which was so small in our studies [Kunzelmann et al. (1992) Pflügers Arch (in press)] that we could not resolve it at the single-channel level. This prompted the question whether these Cl- conductances can be distinguished in terms of their ion selectivity and sensitivity towards inhibitors. Whether these pathways are additive or not was also examined. The present study utilized the whole-cell patch-clamp and the CAN methods. A total of 160 patches were studied. In whole-cell patches 8-(4-chlorophenylthio)-cAMP (cAMP, 0.1 +/- 1 mmol/l) induced a significant depolarization by 5 mV and a twofold increase in conductance (G) from 6.2 +/- 1.5 nS to 11.7 +/- 3.2 nS (n = 15). Total replacement of Cl- by Br- and I- in cAMP-treated cells hyperpolarized the membrane voltage (V) significantly from -35 +/- 2.8 to -39 +/- 3.4 and -45 +/- 3.3 mV respectively, but had no detectable effect on G, which was 11.9 +/- 3.3 nS in the case of Br- and 11.8 +/- 3.3 nS in the case of I-. Hence, the permselectivity of the cAMP pathway was I- > Br- > Cl-, but the conductances for these anions were all indistinguishable.(ABSTRACT TRUNCATED AT 250 WORDS)