Life in the ocean is a constant battle to maintain a healthy ionic balance. Fish excrete acid and base, such as bicarbonate, across their gills to stay in equilibrium with their environment. While disposing of unwanted bicarbonate ions, gill cells in turn generate hydrogen ions that are subsequently carried away in the blood. Martin Tresguerres explains that the H+transporting V-H+-ATPase proteins are an essential component of the base excretion process, but earlier work had suggested that the protein was located in the cell's cytoplasm, well away from the membrane that the hydrogen ions must cross for removal in the blood.
Wondering whether the gill cell's protein trafficking machinery may relocate V-H+-ATPases from the cytoplasm to the cell membrane as part of the excretion process, Tresguerres and his colleagues at the University of Alberta disrupted the dogfish protein trafficking machinery while infusing the fish with bicarbonate to see if they were still able to excrete the excess base (p. 599). Monitoring levels of carbonate in the fish's blood, the team found that the carbonate levels rose; disrupting the protein trafficking system had interrupted the ion pumping process. And when they looked for the V-H+-ATPase proteins in gill cells after the fish experienced a high dose of bicarbonate, the team found that the protein was situated in the gill cell membrane, where they expected to find it if it contributed to base excretion. `Our results strongly suggest that cellular relocation of V-H+-ATPase is necessary for enhanced HCO3-secretion' says Tresguerres.