Swelling-activated, cystic fibrosis transmembrane conductance regulator-augmented ATP release and Cl- conductances in murine C127 cells

1. A hypotonic challenge, but not cAMP stimulation, was found to induce release of ATP measured by the luciferin-luciferase assay from both the murine mammary carcinoma cell line C127i and C127 cells stably transfected with the cDNA for human cystic fibrosis transmembrane conductance regulator (CFTR) protein (C127/CFTR). CFTR expression augmented swelling-induced ATP release by 10-20 times under hypotonic conditions (less than or equal to 80 % osmolality). 2. Glibenclamide failed to suppress swelling-induced ATP release from C127/CFTR cells. In contrast, whole-cell patch-clamp recordings showed that both the cAMP-activated ohmic Cl(-) currents and volume-sensitive outwardly rectifying (VSOR) Cl(-) currents were prominently suppressed by glibenclamide. 3. Gd(3+) markedly blocked swelling-induced ATP release but failed to suppress both cAMP- and swelling-activated Cl(-) currents in the CFTR-expressing cells: Even after pretreatment and during treatment with Gd(3+), VSOR Cl(-) currents were activated normally. 4. The continuous presence of an ATP-hydrolysing enzyme, apyrase, in the bathing solution did not prevent activation of VSOR Cl(-) currents in C127/CFTR cells. 5. The rate of regulatory volume decrease (RVD) in C127/CFTR cells was much faster than that in C127i cells. When apyrase was added to the bathing solution, the RVD rate was retarded in C127/CFTR cells. 6. On balance, the following conclusions can be deduced. First, swelling-induced ATP release is augmented by expression of CFTR but is not mediated by the CFTR Cl(-) channel. Second, swelling-induced ATP release is not mediated by the VSOR Cl(-) channel. Third, the released ATP facilitated the RVD process but is not involved in the activation of VSOR Cl(-) channels in C127/CFTR cells.