Activation of Cl− currents by intracellular chloride in fibroblasts stably expressing the human cystic fibrosis transmembrane conductance regulator

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Abstract
The Cl− conductance of a mouse fibroblast cell line (LTK− cells) that was stably transfected with the human CFTR (cystic fibrosis transmembrane conductance regulator) complementary DNA was studied. Single Cl− channel activity was observed only after treatment of the cells with forskolin, the single-channel conductance being 6.2 ± 0.2 pS with a linear current–voltage relationship. In CFTR+ cells, the whole-cell current at +90 mV increased from 7.3 ± 2.7 pA/pF (n = 12) to 46.1 ± 11.2 pA/pF (n = 5) after addition of dibutyryl-cyclic AMP (10−4 M) to the bath. Increasing the intracellular Cl− concentration to 150 mM activated linear Cl− currents in the absence of cyclic AMP in CFTR+ (n = 42) but not in CFTR− cells (n = 4). Similar Cl− current was also activated by high intracellular I− concentration. These results indicate that the CFTR-induced Cl− conductance in LTK− cells can be activated by either cyclic AMP or high intracellular halide concentrations.Key words: cystic fibrosis transmembrane conductance regulator (CFTR), chloride channel, cyclic AMP, whole-cell patch clamp, single-channel patch clamp.

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