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First published online May 29, 2009
Journal of Experimental Biology 212, 1940-1948 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.026856

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The involvement of H⁺-ATPase and carbonic anhydrase in intestinal HCO₃^– secretion in seawater-acclimated rainbow trout

M. Grosell^1,*, J. Genz¹, J. R. Taylor¹, S. F. Perry² and K. M. Gilmour²

¹ RSMAS, Division of Marine Biology and Fisheries, University of Miami, Miami, FL 33149, USA
² Department of Biology, University of Ottawa, Ottawa, ON, Canada, K1N 6N5

^* Author for correspondence (e-mail: mgrosell{at}rsmas.miami.edu)

Accepted 24 March 2009

Pyloric caeca and anterior intestine epithelia from seawater-acclimated rainbow trout exhibit different electrophysiological parameters with lower transepithelial potential and higher epithelial conductance in the pyloric caeca than the anterior intestine. Both pyloric caeca and the anterior intestine secrete HCO₃^– at high rates in the absence of serosal HCO₃^–/CO₂, demonstrating that endogenous CO₂ is the principal source of HCO₃^– under resting control conditions. Apical, bafilomycin-sensitive, H⁺ extrusion occurs in the anterior intestine and probably acts to control luminal osmotic pressure while enhancing apical anion exchange; both processes with implications for water absorption. Cytosolic carbonic anhydrase (CAc) activity facilitates CO₂ hydration to fuel apical anion exchange while membrane-associated, luminal CA activity probably facilitates the conversion of HCO₃^– to CO₂. The significance of membrane-bound, luminal CA may be in part to reduce HCO₃^– gradients across the apical membrane to further enhance anion exchange and thus Cl^– absorption and to facilitate the substantial CaCO₃ precipitation occurring in the lumen of marine teleosts. In this way, membrane-bound, luminal CA thus promotes the absorption of osmolytes and reduction on luminal osmotic pressure, both of which will serve to enhance osmotic gradients to promote intestinal water absorption.

Key words: marine fish, osmoregulation, proton pump, water absorption, bicarbonate transport

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