Acid-Base Regulation in the Atlantic Hagfish Myxine Glutinosa

Blood acid-base status and net transfers of acidic equivalents to the external environment were studied in hagfish, Myxine glutinosa, infused with ammonium sulphate (4mequivkg⁻¹ NFL⁺) or with sulphuric acid (3mequivkg⁻¹ H⁺). Hagfish extracellular fluids (ECF) play a greater role in acid-base regulation than in teleosts. This is because hagfish have a much larger blood volume relative to teleosts, despite a relatively low blood buffering capacity. Consequently, infusion of ammonium sulphate produced only half of the acidosis produced in marine teleosts in comparable studies, and hagfish readily tolerated a threefold greater direct H⁺ load. Furthermore, the H⁺ load was largely retained and buffered in the extracellular space. Despite smaller acid-base disturbances, rates of net H⁺ excretion to the external environment were, nonetheless, comparable to those of marine teleosts, and net acid excretion persisted until blood acid-base disturbances were corrected. We conclude that the gills of the hagfish are at least as competent for acid-base regulation as those of marine teleosts. The nature of the H⁺ excretion mechanism is discussed.