title: P2Y6 receptor mediates colonic NaCl secretion via differential activation of cAMP-mediated transport.
abstract: Extracellular nucleotides are important regulators of epithelial ion transport. Here we investigated nucleotide-mediated effects on colonic NaCl secretion and the signal transduction mechanisms involved. Basolateral UDP induced a sustained activation of Cl(-) secretion, which was completely inhibited by 293B, a specific inhibitor of cAMP-stimulated basolateral KCNQ1/KCNE3 K(+) channels. We therefore speculated that a basolateral P2Y(6) receptor could increase cAMP. Indeed UDP elevated cAMP in isolated crypts. We identified an epithelial P2Y(6) receptor using crypt [Ca(2+)](i) measurements, RT-PCR, and immunohistochemistry. To investigate whether the rat P2Y(6)elevates cAMP, we coexpressed the P2Y(1) or P2Y(6) receptor together with the cAMP-regulated cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel in Xenopus oocytes. A two-electrode voltage clamp was used to monitor nucleotide-induced Cl(-) currents. In oocytes expressing the P2Y(1) receptor, ATP transiently activated the endogenous Ca(2+)-activated Cl(-) current, but not CFTR. In contrast, in oocytes expressing the P2Y(6)receptor, UDP transiently activated the Ca(2+)-activated Cl(-) current and subsequently CFTR. CFTR Cl(-) currents were identified by their halide conductance sequence. In summary we find a basolateral P2Y(6) receptor in colonic epithelial cells stimulating sustained NaCl secretion by way of a synergistic increase of [Ca(2+)](i) and cAMP. In support of these data P2Y(6) receptor stimulation differentially activates CFTR in Xenopus oocytes.
authors.affiliation: Medizinische Universitätsklinik, Freiburg, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Köttgen
authors.forename: Thomas
authors.initials: T
authors.lastname: Löffler
authors.forename: Christoph
authors.initials: C
authors.lastname: Jacobi
authors.forename: Roland
authors.initials: R
authors.lastname: Nitschke
authors.forename: Hermann
authors.initials: H
authors.lastname: Pavenstädt
authors.forename: Rainer
authors.initials: R
authors.lastname: Schreiber
authors.forename: Sebastian
authors.initials: S
authors.lastname: Frische
authors.forename: Søren
authors.initials: S
authors.lastname: Nielsen
authors.forename: Jens
authors.initials: J
authors.lastname: Leipziger
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D003001:Cloning, Molecular; D003106:Colon / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D007150:Immunohistochemistry; D018715:Microscopy, Video; D009865:Oocytes / Q000378:metabolism; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012965:Sodium Chloride / Q000378:metabolism*; D014981:Xenopus / Q000378:metabolism
chemical_list: D018048:Receptors, Purinergic P2; C099845:purinoceptor P2Y6; D012965:Sodium Chloride; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D015056:1-Methyl-3-isobutylxanthine