The fate of14C infused into the swim bladder of the American eel,Anguilla rostrata

Abstract

The present study analyses the capability of swim-bladder tissue of the American eel (Anguilla rostrata) to incorporate either intermediates of glucose metabolism or blood-borne fatty acids into the swim-bladder lipid fraction. At 29.9 ± 6.0 nmol∙min−1∙g−1wet mass, the activity of acyl-CoA synthetase was about 10-fold higher than the activity of acetyl-CoA carboxylase, a key enzyme required for de novo fatty acid synthesis. The level of fatty acid synthase activity was too low to be detected by the enzymatic test used. When the swim bladder was perfused for 1 h with medium containing 5 mmol∙L−1glucose as the only fuel, 11.5 ± 3.3 nmol glucose∙g−1tissue was incorporated into the lipid pool. When, in addition to 5 mmol∙L−1glucose, 1.1 mmol∙L−1acetate was added to the perfusate, incorporation of acetate into the lipid pool was 3.06 ± 1.14 nmol acetate∙g−1tissue. When 0.41 mmol∙L−1palmitate was added to the glucose-containing perfusate, 144.5 ± 24.2 nmol palmitate∙g−1tissue was incorporated into the lipid pool. These results demonstrate that de novo synthesis of lipids in swim-bladder tissue is only possible at a very low rate and cannot explain the difference in numbers of carbon atoms entering and leaving the swim-bladder wall. Blood-borne fatty acids, however, can be readily taken up and incorporated into swim-bladder lipids.