UTP inhibits Na+ absorption in wild-type and DeltaF508 CFTR-expressing human bronchial epithelia.

Abstract

Ca2+-mediated agonists, including UTP, are being developed for therapeutic use in cystic fibrosis (CF) based on their ability to modulate alternative Cl- conductances. As CF is also characterized by hyperabsorption of Na+, we determined the effect of mucosal UTP on transepithelial Na+ transport in primary cultures of human bronchial epithelia (HBE). In symmetrical NaCl, UTP induced an initial increase in short-circuit current (Isc) followed by a sustained inhibition. To differentiate between effects on Na+ absorption and Cl- secretion, Isc was measured in the absence of mucosal and serosal Cl- (INa). Again, mucosal UTP induced an initial increase and then a sustained decrease that reduced amiloride-sensitive INa by 73%. The Ca2+-dependent agonists histamine, bradykinin, serosal UTP, and thapsigargin similarly induced sustained inhibition (62-84%) of INa. Mucosal UTP induced similar sustained inhibition (half-maximal inhibitory concentration 296 nM) of INa in primary cultures of human CF airway homozygous for the DeltaF508 mutation. BAPTA-AM blunted UTP-dependent inhibition of INa, but inhibitors of protein kinase C (PKC) and phospholipase A2 had no effect. Indeed, direct activation of PKC by phorbol 12-myristate 13-acetate failed to inhibit Na+ absorption. Apyrase, a tri- and diphosphatase, did not reverse inhibitory effects of UTP on INa, suggesting a long-term inhibitory effect of UTP that is independent of receptor occupancy. After establishment of a mucosa-to-serosa K+ concentration gradient and permeabilization of the mucosal membrane with nystatin, mucosal UTP induced an initial increase in K+ current followed by a sustained inhibition. We conclude that increasing cellular Ca2+ induces a long-term inhibition of transepithelial Na+ transport across normal and CF HBE at least partly due to downregulation of a basolateral membrane K+ conductance. Thus UTP may have a dual therapeutic effect in CF airway: 1) stimulation of a Cl- secretory response and 2) inhibition of Na+ transport.

• Authors: D C Devor, J M Pilewski
• Journal: The American journal of physiology (Am J Physiol) Vol. 276 Issue 4 Pg. C827-37 (04 1999) ISSN: 0002-9513 [Print] United States
• PMID: 10199813 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• CFTR protein, human
• Chlorides
• Bumetanide
• Cystic Fibrosis Transmembrane Conductance Regulator
• Amiloride
• Histamine
• Sodium
• Tetradecanoylphorbol Acetate
• Calcium
• Uridine Triphosphate

Topics

• Amiloride (pharmacology)
• Biological Transport (drug effects)
• Bronchi (physiopathology)
• Bumetanide
• Calcium (physiology)
• Cells, Cultured
• Chlorides (metabolism)
• Cystic Fibrosis (genetics, physiopathology)
• Cystic Fibrosis Transmembrane Conductance Regulator (genetics, physiology)
• Histamine (pharmacology)
• Homozygote
• Humans
• Membrane Potentials (drug effects, physiology)
• Mucous Membrane (drug effects, physiopathology)
• Sequence Deletion
• Sodium (metabolism)
• Tetradecanoylphorbol Acetate (pharmacology)
• Uridine Triphosphate (pharmacology)