Modulation of ion transporter expression in gill mitochondrion-rich cells of eels acclimated to low-Na + or-Cl - freshwater

Abstract

In this study, we aimed to establish an experimental model to study the role of the gill mitochondrion-rich cells (MRCs) of freshwater fish in Na + uptake and to examine the effect of adjusting external Na + and Cl - ions on selected ion transporters in gill MRCs. Japanese eels (Anguilla japonica) acclimated to deionized (DI) water for 2 weeks were transferred directly to (a) ion-supplemented artificial freshwater (AF), (b) Na +-deficient AF, or (c) Cl --deficient AF for 2 days. The effects of the transfer on the expression levels of ion transporters in isolated gill cells were investigated. Our data demonstrated that the 2-day acclimation in ion-supplemented AF, Na +-deficient AF, or Cl --deficient AF led to a significant increase in serum osmolarity attributed mainly to an increase in serum Na + and/or Cl - levels when compared with DI-acclimated eel. Significant inductions of V-type H +-ATPase (V-H +-ATPase) and cotransporter (NBC1) mRNA expression in gill MRCs were detected in AF-acclimated fish. In fish acclimated to Na +-deficient AF, mRNA expression levels of V-H +-ATPase, NBC1, and Na +/H +-exchanger-3 (NHE3) were significantly increased in MRCs. Fish acclimated to Cl --deficient AF showed no observable change in expression levels of ion transporters in gill MRCs. In addition, expression levels of ion transporters in pavement cells were stable throughout the 2-day experiments. These data indicate that the level of Na + in freshwater is important for altering the mRNA expression of ion transporters in gill MRCs, which supports the notion that gill MRCs play important roles in freshwater Na + uptake. © 2011 Wiley-Liss, Inc.