Metabolism of extracellular nucleotides in human airways by a multienzyme system

Extracellular nucleotides are involved in the control of mucociliary cleara nce (MCC) in human airways. Because of their therapeutic potential for obst ructive lung diseases such as cystic fibrosis (CF), we investigated nucleot ide metabolism on airway epithelial surfaces. The mucosal surface of human nasal and bronchial epithelial cells in culture dephosphorylated ATP into A DP, AMP, and adenosine. Bronchial cells hydrolyzed ATP at a faster rate tha n nasal cells, 3.8 +/- 0.5 nmol.min(-1) cm(-2) and 2.2 +/- 0.4 nmol.min(-1) cm(-2), respectively. The ratios of ATP/ADP hydrolysis for bronchial and n asal epithelia were 2.9 +/- 0.6 and 2.1 +/- 0.4, respectively. Divalent cat ions were required for ATP hydrolysis (Ca2+ > Mg2+) and pH dependency profi le revealed two peaks, at pH 7.5 ad 9.0. Kinetic analysis supported the coe xpression of more than one ATP-hydrolyzing activity on nasal (K-m = 17 +/- 2 muM, 129 +/- 5 muM, and 405 +/- 12 muM) and bronchial (K-m = 12 +/- 5 muM and 136 +/- 8 muM) epithelial cells. Reverse-transcriptase polymerase chai n reaction confirmed the coexpression of all three families of ATP-hydrolyz ing ectoenzymes: ecto-nucleoside triphosphate diphosphohydrolases, ecto-nuc leotide pyrophosphatase/phosphodiesterases, and alkaline phosphatases. Alto gether, these findings demonstrate the presence of a multienzyme system in human airways, with the capacity to control ATP concentrations under physio logical and pathological conditions. The identification of the major enzyme (s) responsible for ATP hydrolysis in human airways may lead to the develop ment of specific inhibitors that would improve nucleotide-based treatments of MCC in patients with CF. Drug Dev. Res. 52:66-75, 2001. (C) 2001 Wiley-L iss, Inc.