Table 2.

Standard deviation of the glutamate–glutamine cycling flux determined using Monte Carlo analysis when astrocytic dilution is omitted from the two-compartment model^a,^b

Constraints (μmol/g/min)	Mean Vcyc (μmol/g/min)	Relative s.d. Vcycc(%)	Noise level (μmol/g)
None	0.50	438	0.2
	0.27	66	0.1
aVTCA≤0.1, Vefflux = 0.2VGln	0.27	32	0.2
	0.26	21	0.1

V_TCA, tricarboxylic acid cycle flux; V_efflux, rate of glutamine efflux; V_Gln, flux of glutamine synthesis.

^aAll simulations were carried out with a total infusion time of 160 mins and temporal resolution of 5 mins (32 time points). Only the glutamate C4 and glutamine C4 turnover curves were used for extraction of the metabolic fluxes. When V_dil(Gln) is forced to zero ¹³C-labeled glutamine concentration predicted by the model is higher than that shown in Figure 2A. The ¹³C-labeled glutamine concentration with V_dil(Gln) = 0 was made to match that in Figure 2A by reducing the total glutamine concentration to 2.8 mmol/L in the Monte Carlo simulations. This was done in order to simulate the Gruetter et al (2001) model (Shestov et al, 2007) where astroglial dilution was omitted.

^bMean χ² of all simulations lies in the range of 60.2–61.1 with a standard deviation in the range of 10.9–11.3.

^cWith respect to the nominal V_cyc = 0.32 μmol/g/min.