Secreted and Cell-Associated Adenylate Kinase and Nucleoside Diphosphokinase Contribute to Extracellular Nucleotide Metabolism on Human Airway Surfaces

5'-Nucleoside triphosphates (NTP) are present in the liquid covering airway surfaces and mediate important physiologic events through their interaction with P2-nucleotide receptors. Activation of airway P2Y(2) receptors, for example, stimulates ciliary beat frequency, chloride/liquid secretion, and goblet cell degranulation. We, therefore, have studied the metabolic pathways that regulate the concentration of nucleotides on airway surfaces. Stimulation of submucosal gland secretion in the nose was previously found to decrease the concentration of 5'-adenosine triphosphate (ATP) in nasal lavage samples due to the presence of a secreted 5'-nucleoside triphosphatase (NTPase). In this study, gland secretions were further studied and found to also contain adenylate kinase (AK) and nucleoside diphosphokinase (NDPK) activities. Ecto-AK and ecto-NDPK activities were also detected in well-differentiated cultures of superficial nasal epithelia, which reflected a combination of cell-associated and released (into culture media) AK and NDPK activities. This study demonstrates that "ecto-kinases" on airway surfaces (1) emanate from different enzyme families, including both AK and NDPK; (2) are expressed at superficial epithelial surfaces and in submucosal glands; and (3) may be important regulators of nucleotide concentrations on airway surfaces.