title: Serotonin decreases alveolar epithelial fluid transport via a direct inhibition of the epithelial sodium channel.
abstract: Hypoxia and epithelial stretch that are commonly observed in patients with acute lung injury have been shown to promote the release of serotonin (5-hydroxytryptamine, 5-HT) in vitro. However, whether 5-HT contributes to the decrease of alveolar epithelial fluid transport, which is a hallmark of lung injury, is unknown. Thus, we investigated the effect of 5-HT on ion and fluid transport across the alveolar epithelium. 5-HT caused a dose-dependent inhibition of the amiloride-sensitive current across primary rat and human alveolar epithelial type II cell monolayers, but did not affect Na(+)/K(+) ATPase function. Furthermore, we found that the 5-HT induced inhibition of ion transport across the lung epithelium was receptor independent, as it was not prevented by the blockade of 5-HT2R (5-HT receptor 2), 5-HT3R (5-HT receptor 3), or by pretreatment with an intracellular calcium-chelating agent, BAPTA-AM (1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester). In addition, the stimulation of 5-HT1R (5-HT receptor 1), 5-HT2R (5-HT receptor 2), 5-HT4R (5-HT receptor 4), and 5-HT7R (5-HT receptor 7) failed to reproduce the 5-HT effect on amiloride-sensitive sodium transport. We ascertained that 5-HT directly inhibited the function of rat alphabetagamma epithelial sodium channel (ENaC), as determined by heterologous expression of rat ENaC in Xenopus oocytes that do not express endogenous ENaC nor 5-HT receptors (5-HTR). Exposure of mice to hypoxia for 1 hour induced a 30% increase of 5-HT secretion into the distal airways of mice. Finally, the intratracheal instillation of 5-HT inhibited the amiloride-sensitive fraction of alveolar fluid clearance in mice. Together, these results indicate that 5-HT inhibits the amiloride-sensitive fraction of the alveolar epithelial fluid transport via a direct interaction with ENaC, and thus can be an endogenous inhibitor of this ion channel.
authors.affiliation: Department of Anesthesia, Room 3C-38, San Francisco General Hospital, 1001 Potrero Avenue, San Francisco, CA 94110, USA. goolaertsa@anesthesia.ucsf.edu
authors.forename: Arnaud
authors.initials: A
authors.lastname: Goolaerts
authors.forename: Jérémie
authors.initials: J
authors.lastname: Roux
authors.forename: Michael T
authors.initials: MT
authors.lastname: Ganter
authors.forename: Vadim
authors.initials: V
authors.lastname: Shlyonsky
authors.forename: Ahmed
authors.initials: A
authors.lastname: Chraibi
authors.forename: Renauld
authors.initials: R
authors.lastname: Stéphane
authors.forename: Frédérique
authors.initials: F
authors.lastname: Mies
authors.forename: Michael A
authors.initials: MA
authors.lastname: Matthay
authors.forename: Robert
authors.initials: R
authors.lastname: Naeije
authors.forename: Sarah
authors.initials: S
authors.lastname: Sariban-Sohraby
authors.forename: Marybeth
authors.initials: M
authors.lastname: Howard
authors.forename: Jean-Francois
authors.initials: JF
authors.lastname: Pittet
mesh_terms: D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D004848:Epithelium / Q000473:pathology; D006801:Humans; D000860:Hypoxia; D007477:Ions / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011650:Pulmonary Alveoli / Q000378:metabolism*; D051381:Rats; D012701:Serotonin / Q000378:metabolism*; D014132:Trachea / Q000378:metabolism; D014981:Xenopus
chemical_list: D053503:Epithelial Sodium Channels; D007477:Ions; D012701:Serotonin; D000584:Amiloride