Figure 5.

The OGI vs. lactate dependence (lines) in the mammalian brain can be determined from experimental data (cross symbol): resting human/rat brain with OGI = 5.52 (1); active human brain with OGI = 5.16 (6); and seizure activity in rat brain with OCI = 4.14 (1). The total amount of lactate produced in rat brain during biccuculine-induced seizure is 8 mM whereas the resting lactate level in human brain is 0.6 m M. Using the Michaelis-Menten transport kinetics for lactate (Eq. 6) and the OGI relationship (Eq. 2), a relationship can be derived that is independent of T_max. Therefore, changes in lactate (from the seizure point) can be reflected into changes in OGI for a range of K_m values for lactate transport across the blood-brain barrier. The best fit of the model to the scarce data is with K_m of 2.5 mM, which corresponds to T_max of about 0.75 μmol⋅g⁻¹⋅min⁻¹.