title: Nucleotide regulation of paracellular Cl- permeability in natural rabbit airway epithelium.
abstract: In this study, we demonstrate a novel regulatory mechanism by which mucosal nucleotides via P2Y receptors decrease paracellular Cl(-) ion permeability in natural rabbit airway epithelium (in addition to a decrease in active Na(+) absorption). In contrast to primary cultures, the natural airway epithelium is a low-resistance epithelium, and an equivalent circuit model predicts that changes of more than approximately 12% in transepithelial conductance (G (t)) must include an effect on paracellular conductance (G (s)). Mucosal P2Y receptor stimulation with uridine triphosphate (UTP; 200 microM) decreased G (t) by up to 50% (average, 24%) and simultaneously decreased the paracellular Cl(-) permeability (mucosa-to-serosa Cl(-) flux) by 16%, but had no effect on mannitol permeability. The G (t) response to UTP was mimicked and attenuated by ionomycin (1 microM), suggesting a dependence on Ca(2+) (i). Amiloride (100 microM) and hyperosmolarity (+75 mM mannitol) also decreased G (t), indicating a role of cell shrinkage. Elevation of cAMP with forskolin (8 microM) or isoproterenol (10 microM) increased G (t) by 55 and 32%, and forskolin increased paracellular Cl(-) permeability by 37% without affecting mannitol permeability. The opposite effects of Ca(2+) (i) and cAMP on G (t) suggest an autocrine nucleotide signaling sequence where P2Y-dependent decrease in passive, paracellular Cl(-) transport is succeeded by a reversion of this effect due to P1-receptor-stimulated cAMP formation by adenosine originating from a time-dependent breakdown of mucosal ATP.
authors.affiliation: Department of Medical Physiology, The Panum Institute, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen N, Denmark.
authors.forename: Asser Nyander
authors.initials: AN
authors.lastname: Poulsen
authors.forename: Thomas Levin
authors.initials: TL
authors.lastname: Klausen
authors.forename: Peter Steen
authors.initials: PS
authors.lastname: Pedersen
authors.forename: Niels Johannes
authors.initials: NJ
authors.lastname: Willumsen
authors.forename: Ole
authors.initials: O
authors.lastname: Frederiksen
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000584:Amiloride / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D048429:Cell Size; D002712:Chlorides / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D008353:Mannitol / Q000378:metabolism; D009297:Nasal Mucosa / Q000166:cytology / Q000378:metabolism*; D010539:Permeability; D011817:Rabbits; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D026941:Sodium Channel Blockers / Q000378:metabolism; D019108:Tight Junctions / Q000378:metabolism; D014544:Uridine Triphosphate / Q000378:metabolism*
chemical_list: D002712:Chlorides; D018048:Receptors, Purinergic P2; D026941:Sodium Channel Blockers; D008353:Mannitol; D000584:Amiloride; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D002118:Calcium; D014544:Uridine Triphosphate