EXPRESSION OF CYSTIC-FIBROSIS TRANSMEMBRANE CONDUCTANCE REGULATOR ALTERS THE RESPONSES TO HYPOTONIC CELL SWELLING AND ATP OF CHINESE-HAMSTER OVARY CELLS

The aim of this study was to examine whether the stable expression of wild-type cystic fibrosis transmembrane conductance regulator (CFTR) i n Chinese hamster ovary (CHO) cells alters the properties of these cel ls towards hypotonic cell swelling and ATP. According to many previous studies this was not expected a priori, since overexpression of CFTR should not affect the conductive pathways upregulated by the purinergi c agonist or cell swelling. Three types of CHO cells were examined: a control group of normal CHO cells; a group of CFTR-CHO cells stably ex pressing wild-type CFTR at high levels (CHO-CFTR), and a group Delta F 508-CFTR-CHO cells, stably expressing the frequent mutation Delta F508 CFTR (CHO-Delta F508). Whole cell patch-clamp studies were performed to measure the membrane voltage (V-m), the membrane conductance (G(m)) , and the membrane capacitance (C-m). Hypotonic cell swelling (Hypo, 1 50 mosm/l) was used, because it activates Cl- and K+ channels and enab les the cell to extrude KCl in many cells, and ATP because it is known to activate Ca2+-regulated channels in a large variety of cells. Hypo depolarized all three types of cells. This depolarization was accompa nied by an increase in Cl- conductance. The selectivity of the conduct ance was I- greater than or equal to Br- greater than or equal to Cl- in CHO cells, but Cl- = Br = I- in the CFTR cells. Even more surprisin g: ATP (100 mu mol/l) hyperpolarized CHO and Delta F508 cells and pred ominantly enhanced K+ conductance, whilst it depolarized and increased mostly a Cl- conductance in CFTR cells. The selectivity of this anion conductance was atypical for ATP: Br- > Cl- > I-. C-m was increased b y ATP and Hypo in all three types of cells. ATP enhanced cytosolic Ca2 + ([Ca2+](i)) in all three types of cells but did not enhance cAMP. Th ese data indicate that the expression of CFTR profoundly alters the pr operties of CHO cells. Agonists which stimulate characteristic Ca2+-re gulated channels now enhance a Cl- conductance resembling the properti es of CFTR-Cl- conductance.