Relative oxidation of glutamate and glucose by vertebrate erythrocytes

1. Lungfish erythrocytes (RBC), unlike those in other species of fishes, oxidize endogenous glutamate at a higher rate than they oxidize glucose. This pattern closely resembles that found in invertebrates. 2. The exogenous glutamate oxidation rate of RBC from most species of fish as well as other groups of vertebrates is approximately equal to or less than that observed for glucose. 3. These findings suggest that the nucleated RBC of most vertebrates appear to rely less on the TCA cycle for energy production and more on the glycolytic metabolism of carbohydrates. 4. The RBC of lungfish are also distinguished from RBC of other vertebrates by their relatively higher permeability to exogenous substrates. For example, chicken RBC have a glucose accumulation rate which is approximately one third that observed for lungfish RBC at twice the medium glucose concentration. 5. The unique characteristics of lungfish RBC may be related to their adaptation to the high concentrations of urea produced during estivation.