In this section, we provide a measure of the accuracy of the metabolic model by comparing predicted glucose consumption rates to direct measurements for rabbit in vitro. Zurawski et al.
13 collected and cultured rabbit stromal keratocyte, epithelial, and endothelial cells that were grown to confluence in a gas flow humidified incubator with Krebs-Ringers solution at a pH of 7.2 and with varying initial glucose concentrations. For each of the three cell types, glucose concentration versus time is reported for three initial glucose concentrations of 0.9, 0.6, and 0.3 μg/mm
3, giving a total of nine trials. Each of the trials comprises five consecutive measurements taken with an interval of 20 minutes. Zurawski et al.
13 report the average glucose consumption rate for each cell monolayer of each cell line. If it is assumed, following Zurawski et al.,
13 that the average number of cell layers found in the epithelium, stroma, and endothelium are 5, 7.5, and 1, respectively, the glucose consumption rate per unit volume in each corneal layer may be estimated by direct calculation. Zurawski et al.
13 labeled the cell monolayer consumption rates with the approximate initial glucose concentration targeted at the start of each trial. We examined the data presented in Zurawski et al.
13 and estimated the average glucose concentration during each of the nine individual trials. The average glucose concentrations, converted to mM units by assuming a glucose molar mass
MG = 0.18016 kg/mol are given in
Table 4 along with the corresponding glucose consumption rates for each of the corneal layers. As might be anticipated by cellular density, glucose consumption rates in the epithelial and endothelial layers exceed that of the stroma. For example, at a glucose concentration of 5 mM, the epithelial and endothelial glucose consumption rates exceed the stromal rate by factors of 5.0 and 3.7, respectively.