CFTR regulation of intracellular calcium in normal and cystic fibrosis human airway epithelia

In cystic fibrosis airway epithelia, mutation of the CFTR protein causes a reduced response of Cl- secretion to secretagogues acting via cAMP. Using a Ca2+ imaging system, the hypothesis that CFTR activation may permit ATP re lease and regulate [Ca2+], via a receptor-mediated mechanism, is tested in this study. Application of external nucleotides produced a significant incr ease in [Ca2+], in normal (16HBE14o(-) cell line and primary lung culture) and in cystic fibrosis (CFTE29o(-) cell line) human airway epithelia. The p otency order of nucleotides on [Ca2+](i) variation was UTP >> ATP > UDP > A DP > AMP > adenosine in both cell types. The nucleotide [Ca2+], response co uld be mimicked by activation of CFTR with forskolin (20 mu M) in a tempera ture-dependent manner. In 16HBE14o(-) cells, the forskolin-induced [Ca2+], response increased with increasing temperature. In CFTE29o(-) cells, forsko lin had no effect on [Ca2+], at body temperature-forskolin-induced [Ca2+](i ) response in CF cells could only be observed at low experimental temperatu re (14 degrees C) or when cells were cultured at 26 degrees C instead of 37 degrees C. Pretreatment with CFTR channel blockers glibenclamide (100 mu M ) and DPC (100 mu M), with hexokinase (0.5 U/mg), and with the purinoceptor antagonist suramin (100 mu M), inhibited the forskolin [Ca2+], response. T ogether, these results demonstrate that once activated, CFTR regulates [Ca2 +], by mediating nucleotide release and activating cell surface purinocepto rs in normal and CF human airway epithelia.