STUDIES ON THE ENERGY-METABOLISM OF OPOSSUM (DIDELPHIS-VIRGINIANA) ERYTHROCYTES .1. UTILIZATION OF CARBOHYDRATES AND PURINE NUCLEOSIDES

Opossum erythrocytes filtered through cellulose columns were used to estimate their permeability to D-glucose and optimum Pi requirement for D-glucose utilization at pH 7.4 and 8.1. D-Glucose readily penetrated opossum red cells; there was no measurable difference whether plasma or electrolyte solution served as the suspending medium. Optimum extracellular Pi concentration for glucose utilization as indicated by red cell lactate production was pH-dependent, with a sharp optimum of 30 mmol/l at pH 8.1. Whereas glucose, fructose, mannose, dihydroxyacetone, adenosine and inosine were readily utilized at pH 7.4 and Pi 30 mmol/l as shown by net lactate and ATP production by the red cells, galactose and ribose as substrates were not metabolized. In electrolyte, Pi 30 mmol/l, and pH 7.4 glucose utilization by opossum red cells averaged 3.5 .mu.mol, at pH 8.1, 9.5 .mu.mol/ml cells/h were utilized. Red cells suspended in leukocyte-free plasma utilized D-glucose at a rate of 3.0 .mu.mol/ml per h at pH 7.5. Some 7% of D-glucose flowed through the pentose phosphate pathway; this rate increased 11-fold by methylene blue stimulation. The amount of D-glucose recycled through the pentose phosphate pathway increased 300-fold in the presence of the redox dye.