Reciprocal regulation of glucose and glutamine utilization by cultured human diploid fibroblasts

Human diploid fibroblasts utilize both glucose and glutamine as energy sources. The utilization of glutamine by fibroblasts is regulated by glucose, and vice versa. This conclusion is supported by the following observations: (1) essentially identical growth rates were observed in Eagle's minimum essential medium (MEM)3 in which the glucose concentration was either 5.5 mM or was maintained between 25 and 40 micrometer, (2) the total glutamine utilization by fibroblasts increase at least 30% in medium with 25 micrometer to 70 micrometer glucose compared to medium with 5.5 mM glucose, while the rate of glutamine-1 or 5-14C oxidation to CO2 increased 5-fold as the glucose concentration was decreased to zero, (3) 2 mM glutamine inhibited glucose-6-14C oxidation by 88% and stimulated glucose-1-14C by 77% in log phase cells and (4) glutamine oxidation in normal medium contributed approximately 30% of the energy requirement of human diploid fibroblasts.