Intestinal HCO3- secretion and NaCl absorption are essential for counteracting dehydration in marine teleost fish. We investigated how these two processes are coordinated in toadfish. HCO3- stimulated a luminal positive short-circuit current (Isc) in intestine mounted in Ussing chamber, bathed with the same saline solution on the external and internal sides of the epithelium. The Isc increased proportionally to the [HCO3-] in the bath up to 80 mM NaHCO3, and it did not occur when NaHCO3 was replaced with Na+-gluconate or with NaHCO3 in Cl--free saline. HCO3- (20 mM) induced a ∼2.5-fold stimulation of Isc, and this [HCO3-] was used in all subsequent experiments. The HCO3--stimulated I sc was prevented or abolished by apical application of 10 μM bumetanide (a specific inhibitor of NKCC) and by 30 μM 4-catechol estrogen [CE; an inhibitor of soluble adenylyl cyclase (sAC)]. The inhibitory effects of bumetanide and CE were not additive. The HCO3HCO3-- stimulated Isc was prevented by apical bafilomycin (1 μM) 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 HCO3-, and that V-H+-ATPase and intracellular carbonic anhydrase are essential for transducing luminal HCO3 - into the cell by CO2/HCO3- hydration/dehydration. This mechanism putatively coordinates HCO 3- secretion with NaCl and water absorption in toadfish intestine.
|Original language||English (US)|
|Journal||American Journal of Physiology - Regulatory Integrative and Comparative Physiology|
|State||Published - Jul 2010|
- Carbonic anhydrase
- Proton pump
ASJC Scopus subject areas
- Physiology (medical)