Modulation of NaCl absorption by [HCO3-] in the marine teleost intestine is mediated by soluble adenylyl cyclase

作者：Tresguerres Martin^*; Levin Lonny R; Buck Jochen; Grosell Martin

来源：American Journal of Physiology - Regulatory, Integrative and Comparative Physiology, 2010, 299(1): R62-R71.

DOI：10.1152/ajpregu.00761.2009

• NKCC
• cAMP
• carbonic anhydrase
• bumetanide
• proton pump

Tresguerres M, Levin LR, Buck J, Grosell M. Modulation of NaCl absorption by [HCO3-] in the marine teleost intestine is mediated by soluble adenylyl cyclase. Am J Physiol Regul Integr Comp Physiol 299: R62-R71, 2010. First published April 21, 2010; doi:10.1152/ajpregu.00761.2009.-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 (I-sc) 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 similar to 2.5-fold stimulation of I-sc, and this [HCO3-] was used in all subsequent experiments. The HCO3--stimulated I-sc was prevented or abolished by apical application of 10 mu M bumetanide (a specific inhibitor of NKCC) and by 30 mu M 4-catechol estrogen [CE; an inhibitor of soluble adenylyl cyclase (sAC)]. The inhibitory effects of bumetanide and CE were not additive. The HCO3--stimulated I-sc was prevented by apical bafilomycin (1 mu M) 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 HCO3- secretion with NaCl and water absorption in toadfish intestine.

• 出版日期2010-7