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

Abstract

We have measured the metabolic activity in the vascularly isolated, salineperfused swimbladder of the eel (Anguilla anguilla) in order to investigate the pathways for CO2 formation in the gas gland tissue. Concentrations of O2, CO2, 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.Total CO2 production, averaging 55·8 nmol min−1, was about 4·6 times the O2 consumption (mean 12·0 nmol min−1). This suggests that only about 22% of the CO2 is formed by aerobic glucose metabolism. CO2 formation from HCO3− or CO2 washout does not appear to be significant in our experiments with steady perfusion of a saline containing a low level of HCO3−. 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 CO2. The anoxidative CO2 formation appears to be of functional importance for producing the high gas partial pressures of both CO2 and O2 which are required for secretion of these gases into the swimbladder.