Inhibition of amiloride-sensitive epithelial Na(+) absorption by extracellular nucleotides in human normal and cystic fibrosis airways.
Cystic fibrosis (CF) airway epithelia are characterized by enhanced Na(+) absorption probably due to a lack of downregulation of epithelial Na(+) channels by mutant CF transmembrane conductance regulator. Extracellular nucleotides adenosine 5'-triphosphate (ATP) and uridine 5'-triphosphate (UTP) have been shown to activate alternative Ca(2+)-dependent Cl(-) channels in normal and CF respiratory epithelia. Recent studies suggest additional modulation of Na(+) absorption by extracellular nucleotides. In this study we examined the role of mucosal ATP and UTP in regulating Na(+) transport in native human upper airway tissues from patients with 16 patients with CF and 32 non-CF control subjects. To that end, transepithelial voltage and equivalent short-circuit current (I(SC)) were assessed by means of a perfused micro-Ussing chamber. Mucosal ATP and UTP caused an initial increase in lumen-negative I(SC) that was followed by a sustained decrease of I(sc) in both non-CF and CF tissues. The amiloride-sensitive portion of I(SC) was inhibited significantly in normal and CF tissues in the presence of either ATP or UTP. Both basal Na(+) transport and nucleotide-dependent inhibition of amiloride-sensitive I(SC) were significantly enhanced in CF airways compared with non-CF. Nucleotide-mediated inhibition of Na(+) absorption was attenuated by pretreatment with the Ca(2+)-adenosine triphosphatase inhibitor cyclopiazonic acid but not by inhibition of protein kinase C with bisindolylmaleimide. These data demonstrate sustained inhibition of Na(+) transport in non-CF and CF airways by mucosal ATP and UTP and suggest that this effect is mediated by an increase of intracellular Ca(2+). Because ATP and UTP inhibit Na(+) absorption and stimulate Cl(-) secretion simultaneously, extracellular nucleotides could have a dual therapeutic effect, counteracting the ion transport defect in CF lung disease.
Mall
M
M
Universitäts-Kinderklinik, Albert-Ludwigs Universität Freiburg, Freiburg, Germany. mmall@kk1200.ukl.uni-freiburg.de
Wissner
A
A
Gonska
T
T
Calenborn
D
D
Kuehr
J
J
Brandis
M
M
Kunzelmann
K
K
D000042:Absorption / Q000187:drug effects; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000293:Adolescent; D000328:Adult; D000368:Aged; D000584:Amiloride / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002648:Child; D002675:Child, Preschool; D003550:Cystic Fibrosis / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects* / Q000378:metabolism; D005260:Female; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D008297:Male; D008301:Maleimides / Q000494:pharmacology; D008875:Middle Aged; D009296:Nasal Cavity / Q000187:drug effects* / Q000378:metabolism; D009711:Nucleotides / Q000494:pharmacology*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D015398:Signal Transduction; D012964:Sodium / Q000493:pharmacokinetics*; D014544:Uridine Triphosphate / Q000494:pharmacology
D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D009711:Nucleotides; D000584:Amiloride; D000255:Adenosine Triphosphate; D012964:Sodium; D011493:Protein Kinase C; C088060:bisindolylmaleimide; D002118:Calcium; D014544:Uridine Triphosphate