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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Cellular mechanisms of Cl^– transport in trout gill mitochondrion-rich cells

¹Deptartment of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada; and ²Department of Pharmacology, Weill Medical College of Cornell University, New York, New York

Submitted 9 December 2008 ; accepted in final form 6 February 2009

We have studied Cl^– transport mechanisms in freshwater rainbow trout gill mitochondrion-rich (MR) cells using intracellular pH (pH_i) imaging. Scanning electron microscopy demonstrated maintenance of cellular polarity in isolated MR cells. MR cell subtypes were identified by Na⁺ introduction to the bath, and Cl^– transport mechanisms were subsequently examined. Cl^–-free exposure resulted in an alkalinization of pH_i in both MR cell subtypes, which was dependent on HCO₃^– in the bath and inhibited by 1 mM DIDS. Recovery of pH_i from an acidified state in Na⁺-free conditions was also DIDS sensitive. These results are the first functional evidence for Cl^–/HCO₃^– exchangers in fish gill MR cells. A direct switch from NaCl to Cl^–-free conditions caused a pH_i acidification in a subset of MR cells, which was enhanced in the absence of HCO₃^–. The acidification was replaced by an alkalinization when Cl^– removal was performed in the presence of NPPB (500 µM) or EIPA (500 µM). Finally, we found that the Na⁺-induced alkalinization of pH_i found in a previous study is inhibited by EIPA. This inhibitor profile's results suggest the presence of a Cl^–-dependent Na⁺/H⁺ exchange mechanism.

pH_i imaging; NHE; acid/base regulation; anion exchange

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