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Physiol Biochem Zool. 2006 Nov-Dec;79(6):981-96. Epub 2006 Oct 5.

Chloride uptake and base secretion in freshwater fish: a transepithelial ion-transport metabolon?

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Department of Biological Sciences, University of Alberta, Edmonton, Alberta T5G 2E9, Canada.


Despite all the efforts and technological advances during the last few decades, the cellular mechanisms for branchial chloride uptake in freshwater (FW) fish are still unclear. Although a tight 1 : 1 link with HCO-3 secretion has been established, not much is known about the identity of the ion-transporting proteins involved or the energizing steps that allow for the inward transport of Cl- against the concentration gradient. We propose a new model for Cl- uptake in FW fish whereby the combined action of an apical anion exchanger, cytoplasmic carbonic anhydrase, and basolateral V-type H+ -ATPase creates a local [HCO-3] high enough to energize Cl- uptake. Our model is based on analyses of structure-function relationships, reinterpretation of previous results, and novel observations about gill cell subtypes and immunolocalization of the V-H+ -ATPase.

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