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This Article Full Text Full Text (PDF) All Versions of this Article: 292/2/C935    most recent 00604.2005v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Parks, S. K. Articles by Goss, G. G. Search for Related Content PubMed PubMed Citation Articles by Parks, S. K. Articles by Goss, G. G.

MEMBRANE TRANSPORTERS, ION CHANNELS, AND PUMPS

Interactions between Na⁺ channels and Na⁺-HCO₃^– cotransporters in the freshwater fish gill MR cell: a model for transepithelial Na⁺ uptake

Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada

Submitted 2 December 2005 ; accepted in final form 24 September 2006

Isolated mitochondria-rich (MR) cells from the rainbow trout gill epithelium were subjected to intracellular pH (pH_i) imaging with the pH-sensitive dye BCECF-AM. MR cells were categorized into two distinct functional subtypes based on their ability to recover pH_i from an NH₄Cl-induced acidification in the absence of Na⁺. An apparent link between resting pH_i and Na⁺-independent pH_i recovery was made. We observed a unique pH_i acidification event that was induced by extracellular Na⁺ addition. This further classified the mixed MR cell population into two functional subtypes: the majority of cells (77%) demonstrated the Na⁺-induced pH_i acidification, whereas the minority (23%) demonstrated an alkalinization of pH_i under the same circumstances. The focus of this study was placed on the Na⁺-induced acidification and pharmacological analysis via the use of amiloride and phenamil, which revealed that Na⁺ uptake was responsible for the intracellular acidification. Further experiments revealed that pH_i acidification could be abolished when Na⁺ was allowed entry into the cell, but the activity of an electrogenic Na⁺-HCO₃^– cotransporter (NBC) was inhibited by DIDS. The electrogenic NBC activity was supported by a DIDS-sensitive, Na⁺-induced membrane potential depolarization as observed via imaging of the voltage-sensitive dye bis-oxonol. We also demonstrated NBC immunoreactivity via Western blotting and immunohistochemistry in gill tissue. We propose a model for transepithelial Na⁺ uptake occurring via an apical Na⁺ channel linked to a basolateral, electrogenic NBC in one subpopulation of MR cells.

epithelial sodium channels; sodium-induced acidification; amiloride; phenamil; DIDS; acid-base; peanut lectin agglutinin binding; membrane potential; BCECF-AM; bis-oxonol; ion uptake

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