CFTR Regulation of Intracellular Calcium in Normal and Cystic Fibrosis Human Airway Epithelia

Abstract

In cystic fibrosis airway epithelia, mutation of the CFTR protein causes a reduced response of Cl(-) secretion to secretagogues acting via cAMP. Using a Ca(2+) imaging system, the hypothesis that CFTR activation may permit ATP release and regulate [Ca(2+)](i) via a receptor-mediated mechanism, is tested in this study. Application of external nucleotides produced a significant increase in [Ca(2+)](i) in normal (16HBE14o(-) cell line and primary lung culture) and in cystic fibrosis (CFTE29o(-) cell line) human airway epithelia. The potency order of nucleotides on [Ca(2+)](i) variation was UTP >> ATP > UDP > ADP > AMP > adenosine in both cell types. The nucleotide [Ca(2+)](i) response could be mimicked by activation of CFTR with forskolin (20 microm) in a temperature-dependent manner. In 16HBE14o(-) cells, the forskolin-induced [Ca(2+)](i) response increased with increasing temperature. In CFTE29o(-) cells, forskolin had no effect on [Ca(2+)](i) at body temperature-forskolin-induced [Ca(2+)](i) response in CF cells could only be observed at low experimental temperature (14 degrees C) or when cells were cultured at 26 degrees C instead of 37 degrees C. Pretreatment with CFTR channel blockers glibenclamide (100 microm) and DPC (100 microm), with hexokinase (0.5 U/mg), and with the purinoceptor antagonist suramin (100 microm), inhibited the forskolin [Ca(2+)](i) response. Together, these results demonstrate that once activated, CFTR regulates [Ca(2+)](i) by mediating nucleotide release and activating cell surface purinoceptors in normal and CF human airway epithelia.