Glucose metabolism in the calf lens

Carbohydrate metabolism in lens homogenates was evaluated using uniformly labeled [14C]-glucose. Metabolites were separated using HPLC and the distribution of 14C among metabolic pathways was determined. Under the standard incubation conditions employed (pH 7.4, 37 degrees C, 5 mM glucose) 40% of the glucose consumed forms lactate. The amount of 14C found in sorbitol and alpha-glycerol phosphate is 1-2%. This pathway distribution is essentially independent of glucose concentration from 2 to 35 mM. Over this range, lactate production is relatively constant at 2-3 mumol 7 hr-1. At 35 mM glucose, sorbitol production increases to 0.182 from 0.036 mumol 7 hr-1 at 5 mM glucose. The level of ATP is clearly a very significant factor in the regulation of glycolytic rate. An increase in ATP concentration from 1 to 3 mM results in a decrease in the rate of lactate production from 2.09 to 0.404 mumol 7 hr-1. The NAD/NADH ratio is significant in the distribution between lactate and alpha-GP. An increase in the level of NADP or NADPH increases sorbitol production as well as alpha-GP production. A computer program was developed to model the experimental incubation system. The calculated results are in agreement with the experimental in showing effects of ATP and perturbations of enzyme cofactor concentrations.