Betz et al. [327] fitted their influx data using39 Tinf=Tapp/Kapp+cplasmawith apparent values of the Michaelis–Menten constants shown in Table 8 for brains with cisf set by pre-exposure to different cplasma. As cisf is increased both the apparent transport maximum and the apparent Michaelis constants for influx increase which is evidence for both competition and trans-stimulation. Betz et al. interpreted the variation of the apparent constants with cisf in terms of Eq. 33. As shown in the Additional file 1, all of the data for influx can be described empirically using Eq. 35. It is possible to calculate the rate of efflux, under steady-state conditions using Teff = Tinf − Tnet = Tinf − CMRglc for the combinations of cplasma and cisf seen at steady-state. Furthermore, if influx is described empirically by Eq. 33 then Eq. 34 is expected to be a reasonable description of efflux over the same range of concentrations and thus can be used to calculate the efflux for all combinations of concentrations using the fitted empirical constants.
Table 8 Parameters obtained by Betz et al. [327] from fits of the simple Michaelis–Menten expression Tinf = Tapp/(Kapp + cplasma) to glucose influx versus plasma concentration, cplasma, for preset concentrations of glucose in the brain, cisf
cisf/mM 6.11 16.8 26.3 43.9 56
Kapp/mM 8.46 11.2 17.7 28.2 37.7
Tapp/µmol g−1 min−1 1.61 1.84 2.21 2.68 3.83