QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online October 7, 2008
Journal of Experimental Biology 211, 3306-3314 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.020776

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Ahmed, K. H. Articles by Pelster, B. Search for Related Content PubMed PubMed Citation Articles by Ahmed, K. H. Articles by Pelster, B. Social Bookmarking                         What's this?

Ionic determinants of pH of acidic compartments under hypertonic conditions in trout hepatocytes

Khaled H. Ahmed and Bernd Pelster^*

Institut für Zoologie and Center of Molecular Biosciences, Leopold Franzens Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria

^* Author for correspondence (e-mail: bernd.pelster{at}uibk.ac.at)

Accepted 20 August 2008

Exposure of trout hepatocytes to hypertonicity induced a decrease in acridine orange (AO) fluorescence, indicating a corresponding decrease in pH inside the lumen of acidic compartments (pH_L). Pre-exposure of cells to the specific V-ATPase inhibitor bafilomycin A1 (0.3 µmol l^–1) increased AO fluorescence – unmasking H⁺ leaks under steady-state conditions – and partially removed the hypertonicity-induced pH_L decrease. The sustainability of the luminal acidification, but not the acidification itself, appeared to depend on a low K⁺ and a high Cl^– conductance under hypertonic conditions. Increasing K⁺ conductance using the specific ionophore valinomycin (10 µmol l^–1) or removal of extracellular Cl^– after an instant drop in AO fluorescence resulted in a reversal of luminal acidity. The alkalinization measured under hypertonic conditions in the absence of Cl^– was largely attenuated when cells were bathed in HCO₃^–-free medium, signifying the possible presence of Cl^–/HCO₃^– exchange. Under steady-state conditions, while a slight and brief pH_L increase was measured upon exposure of cells to valinomycin, Cl^– removal, unexpectedly, induced a decrease in pH_L, indicating a role for extracellular Cl^– in limiting luminal acidification. This was confirmed by the substantial pH_L decrease measured upon exposure of cells to the anion exchanger inhibitor SITS (0.5 mmol l^–1). Furthermore, hypertonicity-induced acidification was still noticeable in the presence of SITS. On the other hand, the hypertonicity-induced acidification was significantly reduced in the absence of extracellular Na⁺ or Ca²⁺. However, BAPTA-AM induced an increase in steady-state pH_L that was independent of V-ATPase inhibition. Moreover, the BAPTA-induced alkalinization was still apparent after depletion of intracellular Ca²⁺ using the Ca²⁺ ionophore A23187 in Ca²⁺-free medium. We conclude that pH_L of trout hepatocytes is sensitive to hypertonicity and ionic determinants of hypertonicity. Thus, changes in pH_L should be considered when studying pH adaptations to hypertonic stress.

Key words: trout hepatocyte, acidic compartments, V-ATPase, hypertonicity, acridine orange

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?