Transport of glucose across the blood-brain barrier: reevaluation of the accelerative exchange diffusion.

In an earlier study of glucose transport across the blood-brain barrier it was concluded that the kinetic transport constants increase as the brain glucose concentration increases, a finding that was attributed to accelerative exchange diffusion (Betz et al. 1975). The conclusion, however, relied upon application of a commonly used simplified treatment of tracer extraction data. In this study it is demonstrated that the simplified treatment is applicable only in the case of zero brain glucose concentration, and a more general model for determination of the kinetic constants is developed. Re-analysis by this model of the data of Betz et al. (1975)--comprising a range of brain glucose concentrations--gave kinetic constants which did not vary significantly over a wide range of brain glucose concentrations. For brain glucose concentrations up to about 12 mmol 1(-1), the kinetic constants obtained for glucose transport across the blood-brain barrier are Km = 6.18 +/- 0.38 mmol 1(-1) Vmax = 1.65 +/- 0.06 mu mol g -1 min -1.