The marble goby oxyeleotris marmoratus activates hepatic glutamine synthetase and detoxifies ammonia to glutamine during air exposure
Ammonia levels in various tissues of the marble goby Oxyeleotris marmoratus remained constant throughout a 72 h period of air exposure. The rate of ammonia excretion in these experimental fish decreased to approximately one-fifth of that of the submerged control. Ammonia was not converted to urea during air exposure because there were no significant increases in urea content in the tissues. Also, urea excretion rate was lowered to one-fiftieth that of the submerged fish. After 24 h of air exposure, there was a significant increase in muscle glutamine content, which peaked at 48 h. The increase in glutamine content could account for the decreases in the amounts of ammonia and urea excretion during air exposure. The specific activities of hepatic glutamate dehydrogenase (amination) and glutamine synthetase in these experimental fish increased threefold and thirtyfold, respectively, in comparison with the submerged controls. Thus, O. marmoratus appears to be the first known teleost that responds to air exposure by activating hepatic glutamine synthetase to detoxify internally produced ammonia.
Jow
LY
Department of Biological Sciences, National University of Singapore, Kent Ridge, Singapore 119260, Republic of Singapore, Biology Division, School of Science, National Institute of Education, Nanyang Technological University, Bukit Timah,
Chew
SF
Lim
CB
Anderson
PM
Ip
YK