title: Guanylin activates Cl(-) secretion into the lumen of seawater eel intestine via apical Cl(-) channel under simulated in vivo conditions.
abstract: Guanylin (GN) action on seawater eel intestine was examined under simulated in vivo conditions, where isotonic luminal fluid has low NaCl and high MgSO4 (MgSO4 Ringer). In Ussing chamber, MgSO4 Ringer induced serosa-negative potential difference (PD) even after bumetanide treatment, which is due to the higher paracellular Na(+) permeability over Cl(-), as confirmed by the replacement by MgCl2 (no Cl(-) gradient) or Na2SO4 Ringer (no Na(+) gradient). Luminal GN reversed serosa-negative PD, probably by enhancing Cl(-) secretion into the lumen, as the GN effect was blocked by apical Cl(-) channel blockers [diphenylamine-2-carboxylic acid (DPC), 5-nitro-2-(3-phenylpropylamino) benzoic acid, glibenclamide but not cystic fibrosis transmembrane regulator (CFTR)inh-172] or replacement of luminal fluid by MgCl2 Ringer. The blockers' effect was undetectable when normal Ringer was on both sides. In the sac preparation, NaCl secretion occurred into the lumen (Na(+) > Cl(-)), and GN further enhanced Cl(-) secretion (Cl(-) > Na(+)), resulting in water secretion. These GN effects were also blocked by DPC. Quantitative analyses showed that isotonic NaCl is absorbed when luminal fluid is normal Ringer, but, when luminal fluid is MgSO4 Ringer, hypertonic NaCl, almost equivalent to seawater, is secreted into the lumen after GN. These results indicate that GN stimulates the secretion of hypertonic NaCl into the lumen of seawater eel intestine, like rectal gland of marine elasmobranchs, to get rid of excess NaCl although marine teleost intestine is thought to have only absorptive-type cells with a unique Na-K-Cl cotransport system. The secreted NaCl may activate the cotransport system and further help absorb water in the final segment of seawater eel intestine.
authors.affiliation: Laboratory of Physiology, Department of Marine Bioscience, Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Ando
authors.affiliation: Laboratory of Physiology, Department of Marine Bioscience, Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba, Japan takei@aori.u-tokyo.ac.jp.
authors.forename: Yoshio
authors.initials: Y
authors.lastname: Takei
mesh_terms: D000818:Animals; D018118:Chloride Channels / Q000187:drug effects* / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism*; D004524:Eels / Q000378:metabolism*; D005768:Gastrointestinal Hormones / Q000494:pharmacology*; D006801:Humans; D007408:Intestinal Absorption / Q000187:drug effects; D007413:Intestinal Mucosa / Q000187:drug effects* / Q000378:metabolism; D007419:Intestinal Secretions / Q000187:drug effects* / Q000378:metabolism; D007552:Isotonic Solutions / Q000378:metabolism; D008564:Membrane Potentials; D049990:Membrane Transport Modulators / Q000494:pharmacology; D045265:Natriuretic Peptides / Q000494:pharmacology*; D000077331:Ringer's Solution; D012462:Saline Solution, Hypertonic / Q000378:metabolism; D012623:Seawater; D013997:Time Factors; D014867:Water / Q000378:metabolism
chemical_list: D018118:Chloride Channels; D002712:Chlorides; D005768:Gastrointestinal Hormones; D007552:Isotonic Solutions; D049990:Membrane Transport Modulators; D045265:Natriuretic Peptides; D012462:Saline Solution, Hypertonic; D014867:Water; C072685:guanylin; D000077331:Ringer's Solution
keywords: Cl− channel; guanylin; luminal MgSO4 solution; transcellular Cl− secretion; water secretion