Metabolism of the Perfused Swtmbladder of the European EEL: Oxygen, Carbon Dioxide, Glucose and Lactate Balance

We have measured the metabolic activity in the vascularly isolated, salineperfused swimbladder of the eel ( Anguilla anguilla ) in order to investigate the pathways for CO 2 formation in the gas gland tissue. Concentrations of O 2 , CO 2 , glucose and lactate were measured in the arterial inflow and venous outflow of the swimbladder, and metabolic rates were calculated by the direct Fick principle. 1. Total CO 2 production, averaging 55.8nmol min −1 , was about 4.6 times the O 2 consumption (mean 12.0nmol min −1 ). This suggests that only about 22% of the CO 2 is formed by aerobic glucose metabolism. 2. CO 2 formation from HCO 3 − or CO 2 washout does not appear to be significant in our experiments with steady perfusion of a saline containing a low level of HCO 3 − . 3. The ratio of lactate production to glucose uptake averaged 1.2, indicating that only 60% of the glucose is converted to lactate. Since only 1–2% of the glucose was found to be oxidized (2 nmol min −1 ), the extra glucose appears to be anoxidatively metabolized to CO 2 . 4. The anoxidative CO 2 formation appears to be of functional importance for producing the high gas partial pressures of both CO 2 and O 2 which are required for secretion of these gases into the swimbladder.