title: Atrial natriuretic factor stimulates efflux of cAMP in rat exocrine pancreas via multidrug resistance-associated proteins.
abstract: OBJECTIVE
  Atrial natriuretic factor (ANF) prevents increases in intracellular levels of cAMP that are induced by secretin in the exocrine pancreas. We investigated the contribution of cyclic adenosine monophosphate (cAMP) efflux to ANF inhibition of secretin signaling.
  
  
  METHODS
  Intracellular and extracellular cAMP were measured by radio-binding assays in isolated pancreatic acini exposed to secretin and other secretagogues, alone or with ANF. Levels of messenger RNA for multidrug resistance-associated protein (MRP)4, MRP5, and MRP8 were measured by real-time polymerase chain reaction. MRP4 was knocked down in AR42J cells by small interfering RNA. In vivo studies were performed in rats.
  
  
  RESULTS
  Pancreatic secretagogues increased levels of intracellular cAMP, but only secretin and vasoactive intestinal peptide promoted cAMP efflux; efflux was increased by ANF, through signaling via natriuretic peptide receptor-C and phospholipase C-protein kinase C. In time-course studies with active phosphodiesterases, levels of intracellular and extracellular cAMP increased earlier after the addition of secretin and ANF (1 min) than after the addition of secretin alone (3 min). Similar kinetic patterns occurred with a phosphodiesterase inhibitor. A probenecid-sensitive transporter mediated cAMP egression. The main cAMP transporter, MRP4, was expressed in AR42J cells and pancreas. cAMP egression occurred in AR42J cells exposed to secretin, but this response was reduced in cells that expressed MRP4 small interfering RNA. In rats, levels of cAMP in plasma and pancreatic juice increased after infusion with secretin alone or secretin plus ANF.
  
  
  CONCLUSIONS
  ANF signals via natriuretic peptide receptor-C coupled to the phospholipase C-protein kinase C pathway to increase secretin-induced efflux of cAMP, probably through MPR-4. Cyclic AMP extrusion might be a mechanism, in addition to phosphodiesterase action, to regulate intracellular cAMP levels in pancreatic acinar cells.
authors.affiliation: Cátedras de Fisiopatología, Facultad de Farmacia y Bioquímica, Universidad de Buenos Aires, Buenos Aires, Argentina.
authors.forename: Myrian R
authors.initials: MR
authors.lastname: Rodríguez
authors.forename: Federico
authors.initials: F
authors.lastname: Diez
authors.forename: Maria S
authors.initials: MS
authors.lastname: Ventimiglia
authors.forename: Vanina
authors.initials: V
authors.lastname: Morales
authors.forename: Sabrina
authors.initials: S
authors.lastname: Copsel
authors.forename: Marcelo S
authors.initials: MS
authors.lastname: Vatta
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Davio
authors.forename: Liliana G
authors.initials: LG
authors.lastname: Bianciotti
mesh_terms: D000818:Animals; D009320:Atrial Natriuretic Factor / Q000378:metabolism*; D040501:Calgranulin A / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D000242:Cyclic AMP / Q000378:metabolism*; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics / Q000378:metabolism*; D046790:Pancreas, Exocrine / Q000378:metabolism*; D010190:Pancreatic Neoplasms; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering; D051381:Rats; D017207:Rats, Sprague-Dawley; D012633:Secretin / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D010738:Type C Phospholipases / Q000378:metabolism; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism
chemical_list: D009320:Atrial Natriuretic Factor; D040501:Calgranulin A; D000242:Cyclic AMP; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D011493:Protein Kinase C; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D012633:Secretin; D010738:Type C Phospholipases; D014660:Vasoactive Intestinal Peptide; C489542:Abcc4 protein, rat; C492375:Abcc5 protein, rat