Meeting Abstract

6.2  Jan. 4  Molecular identification and expression of a V-type H⁺-ATPase in the gills of euryhaline barramundi (Lates calcarifer). WEAKLEY, J.C.; CLAIBORNE, J.B.; EDWARDS, S.L.**; James Cook University; Georgia Southern University; James Cook University susan.edwards@jcu.edu.au

In fishes, most acid-base imbalances in the short term are moderated by blood and tissue buffering to lessen the impact of acid/base fluctuations. Limitations to buffering require that the final compensation for alterations in pH is by the transepithelial excretion of the excess acid or base from the fish to the ambient water. Euryhaline fishes and moderately euryhaline species such as the barramundi (Lates calcarifer), have the physiological ability to move between waters of various salinities and are often exposed to rapid changes in ionic gradients that impact acid-base exchanges. It has recently been proposed that euryhaline fishes may utilize both V-type H⁺ATPase and Na⁺/H⁺ exchanger mechanisms located in the branchial epithelium to regulate systemic pH, and that the differential expression of the acid/base relevant transporters is governed by environmental salinity. This study has used molecular and immunohistochemical approaches to identify of the presence of a V-type H⁺ATPase in the gill of the euryhaline barramundi. The barramundi V-type H⁺ATPase shares a 97% amino acid identity with other known vertebrate V-type H⁺ATPase cDNAs and is localised to a subpopulation of mitochondrial rich cells in the gill epithelium. In addition, results from H⁺ efflux analysis on animals acclimated to a range of environmental salinities and exposed to 1% CO2, demonstrated that barramundi placed in higher salinities displayed the greatest net H⁺ excretion overall, highlighting the importance of external counter ion (Na⁺) availability and the absolute rate of H⁺ excretion. Initial analysis on terminal gill samples collected during H⁺ efflux studies, show a pattern of increased V-type H⁺ATPase and Na⁺/K⁺-ATPase protein expression correlated to an increased environmental salinity and increased rate of net H⁺ efflux.