부산대학교 도서관

Osmoregulation in the eel requires that NaCl is pumped across the gill epithelium, inwards in the freshwater eel and outwards in the seawater eel. It has been proposed that the transfer of NaCl takes place in mitochondria-rich "chloride cells" and is effected by (Na++ K+)-dependent ATPase. The work of this thesis confirmed that the chloride cells of gills were rich in (Na++ K+)-dependent ATPase and a mitochondrial marker enzyme, succinic dehydrogenase. Both enzymes were shown to have higher activities in the gills of seawater eels, a consequence of the increased salt load to be pumped across the gill epithelium in sea water. (Na++ K+)-dependent ATPases prepared from freshwater and seawater gills were examined on the basis of subcellular distribution, kinetic properties and subunit structure and found to be indistinguishable. Thus, it is likely that the same enzyme pumps NaCl across the gill epithelium in both directions. Adaptation of immature yellow freshwater eels to sea water resulted in an increase in the percentage of chloride cells in the gill followed by an increase in the activities of (Nat+ }.)-dependent ATPase and succinic dehydrogenase. However, adaptation of cature freshwater eels to sea water revealed that the cature silver eel in fresh water is ready for life in sea water. There were no differences in either the percentage of chloride cells or the activity of (Na ++ K+)-dependent ATPase in the gills of the latter fish. Differences were found in the structures of freshwater and seawater chloride cells which could account for the inward pumping of NaCl in fresh water and the outward pumping of NaCl in sea water. Models of mechanisms for pumping NaCl across cellular epithelia were extended to include the stoicheiometry of the transfer of ions and the direction of NaCl pumping effected by (Na ++ K+)-dependentATPase.