Modulation of NaCl absorption by [HCO(3)(-)] in the marine teleost intestine is mediated by soluble adenylyl cyclase.
Intestinal HCO(3)(-) secretion and NaCl absorption are essential for counteracting dehydration in marine teleost fish. We investigated how these two processes are coordinated in toadfish. HCO(3)(-) stimulated a luminal positive short-circuit current (I(sc)) in intestine mounted in Ussing chamber, bathed with the same saline solution on the external and internal sides of the epithelium. The I(sc) increased proportionally to the [HCO(3)(-)] in the bath up to 80 mM NaHCO(3), and it did not occur when NaHCO(3) was replaced with Na(+)-gluconate or with NaHCO(3) in Cl(-)-free saline. HCO(3)(-) (20 mM) induced a approximately 2.5-fold stimulation of I(sc), and this [HCO(3)(-)] was used in all subsequent experiments. The HCO(3)(-)-stimulated I(sc) was prevented or abolished by apical application of 10 muM bumetanide (a specific inhibitor of NKCC) and by 30 microM 4-catechol estrogen [CE; an inhibitor of soluble adenylyl cyclase (sAC)]. The inhibitory effects of bumetanide and CE were not additive. The HCO(3)(-)-stimulated I(sc) was prevented by apical bafilomycin (1 microM) and etoxolamide (1 mM), indicating involvement of V-H(+)-ATPase and carbonic anhydrases, respectively. Immunohistochemistry and Western blot analysis confirmed the presence of an NKCC2-like protein in the apical membrane and subapical area of epithelial intestinal cells, of Na(+)/K(+)-ATPase in basolateral membranes, and of an sAC-like protein in the cytoplasm. We propose that sAC regulates NKCC activity in response to luminal HCO(3)(-), and that V-H(+)-ATPase and intracellular carbonic anhydrase are essential for transducing luminal HCO(3)(-) into the cell by CO(2)/HCO(3)(-) hydration/dehydration. This mechanism putatively coordinates HCO(3)(-) secretion with NaCl and water absorption in toadfish intestine.
Tresguerres
Martin
M
Department of Pharmacology, Weill Cornell Medical College, New York, New York 10065, USA. mat2031@med.cornell.edu
Levin
Lonny R
LR
Buck
Jochen
J
Grosell
Martin
M
D000042:Absorption; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D024541:Batrachoidiformes / Q000502:physiology*; D002034:Bumetanide / Q000494:pharmacology; D002256:Carbonic Anhydrases / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000502:physiology*; D012965:Sodium Chloride / Q000378:metabolism*
D002034:Bumetanide; D012965:Sodium Chloride; D002256:Carbonic Anhydrases; D000262:Adenylyl Cyclases
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