Regulation of intracellular Ca2+ by CFTR in Chinese hamster ovary cells

In cystic fibrosis, the mutation of the CFTR protein causes reduced transep ithelial Cl- secretion. As recently proposed, beside its role of Cl- channe l, CFTR may regulate the activity of other channels such as a Ca2+-activate d Cl- channel. Using a calcium imaging system, we show, in adenovirus-CFTR infected Chinese Hamster Ovary (CHO) cell monolayers, that CFTR can act as a regulator of intracellular [Ca2+](i) ([Ca2+](i)), involving purino-recept ors. Apical exposure to ATP or UTP produced an increase in ([Ca2+](i) in no ninfected CHO cell monolayers (CHO-WT), in CHO monolayers infected with an adenovirus-CFTR (CHO-CFTR) or infected with an adenovirus-lacZ (CHO-LacZ). The transient [Ca2+](i) increase produced by ATP or UTP could be mimicked b y activation of CFTR with forskolin (20 mu M) in CHO-CFTR confluent monolay ers. However, forskolin had no significant effect on [Ca2+](i) in noninfect ed CHO-WT or in CHO-LacZ cells. Pretreatment with pu rino-receptor antagoni sts such as suramin (100 mu M) or reactive blue-2. (100 mu M), and with hex okinase (0.28 U/mg) inhibited the [Ca2+](i) response to forskolin in CHO-CF TR infected cells. Taken together, our experiments provide evidence for pur ino-receptor activation by ATP released from the cell and regulation of [Ca 2+](i) by CFTR in CHO epithelial cell membranes.