cyclic-gmp and cystic-fibrosis-transmembrane-conductance-regulator-(505-511)

Both purinergic stimulation and activation of cystic fibrosis transmembrane conductance regulator (CFTR) increases Cl(-) secretion and inhibit amiloride-sensitive Na(+) transport. CFTR has been suggested to conduct adenosine 5'-triphosphate (ATP) or to control ATP release to the luminal side of epithelial tissues. Therefore, a possible mechanism on how CFTR controls the activity of epithelial Na(+) channels (ENaC) could be by release of ATP or uridine 5'-triphosphate (UTP), which would then bind to P2Y receptors and inhibit ENaC. We examined this question in native tissues from airways and colon and in Xenopus oocytes. Inhibition of amiloride-sensitive transport by both CFTR and extracellular nucleotides was observed in colon and trachea. However, nucleotides did not inhibit ENaC in Xenopus oocytes, even after coexpression of P2Y(2) receptors. Using different tools such as hexokinase, the P2Y inhibitor suramin or the Cl(-) channel blocker 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), we did not detect any role of a putative ATP secretion in activation of Cl(-) transport or inhibition of amiloride sensitive short circuit currents by CFTR. In addition, N(2),2'-O-dibutyrylguanosine 3',5'-cyclic monophosphate (cGMP) and protein kinase G (PKG)-dependent phosphorylation or the nucleoside diphosphate kinase (NDPK) do not seem to play a role for the inhibition of ENaC by CFTR, which, however, requires the presence of extracellular Cl(-).

Topics: 1-Methyl-3-isobutylxanthine; Adenosine Triphosphate; Amiloride; Animals; Colon; Cyclic GMP; Cyclic GMP-Dependent Protein Kinases; Cystic Fibrosis Transmembrane Conductance Regulator; Electric Conductivity; Enzyme Inhibitors; Epithelial Sodium Channels; In Vitro Techniques; Mice; Nucleoside-Diphosphate Kinase; Oocytes; Peptide Fragments; Receptors, Purinergic P2; Receptors, Purinergic P2Y2; Sodium Channels; Uridine Triphosphate; Xenopus