CONTRIBUTION OF THE PENTOSE PHOSPHATE SHUNT TO THE FORMATION OF CO2 IN SWIMBLADDER TISSUE OF THE EEL

The contribution of the pentose phosphate shunt to glucose metabolism in the swimbladder tissue of the American eel Anguilla rostrata has been evaluated by comparing the rate of 14CO2 and [14C]lactate production from [1-14C]glucose and [6-14C]glucose. In blood-perfused swimbladder preparations, 0.18±0.07 nmol min-1 of [6-14C]glucose and 3.19±0.57 nmol min-1 of [1-14C]glucose were converted to CO2. The rate of [14C]glucose conversion to [14C]lactate was about the same in preparations perfused with [6-14C]glucose and with [1-14C]glucose. This may indicate that the C5 skeleton formed in the pentose phosphate shunt is not returned to glycolysis and converted to lactate. Although gas deposition was usually not measurable in these blood-perfused swimbladder preparations, 14CO2 was detected in the eel swimbladder gas of preparations perfused with [1-14C]glucose, but not in preparations perfused with [6-14C]glucose. The results confirm the hypothesis that, in the eel swimbladder epithelium, some of the glucose taken up from the blood is metabolized in the pentose phosphate shunt. This results in the formation of CO2, which is released into the swimbladder as well as into the bloodstream.