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High‐ and Low‐Affinity Transport of D‐Glucose from Blood to Brain
Author(s) -
Gjedde Albert
Publication year - 1981
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1981.tb00587.x
Subject(s) - chemistry , permeability (electromagnetism) , diffusion , glucose transporter , kinetics , biophysics , biochemistry , membrane , endocrinology , biology , insulin , thermodynamics , physics , quantum mechanics
Measurements of the unidirectional blood‐brain glucose flux in rat were incompatible with a single set of kinetic constants for transendothelial transport. At least two transfer mechanisms were present: a high‐affinity, low‐capacity system, and a low‐affinity, high‐capacity system. The low‐affinity system did not represent passive diffusion because it distinguished between D‐and L‐glucose. The T max and K m , for the high‐affinity system were 0.16 mmol 100 g −1 min −1 and 1 mM; for the low‐affinity system, ∼ 5 mmol 100 g −1 min −1 and ∼ 1 M. With these values, physiological glucose concentrations were not sufficient to saturate the low‐affinity system. In normoglycemia, therefore, three independent pathways of glucose transport from blood to brain appear to exist: a high‐affinity facilitated diffusion pathway of apparent permeability 235·10 −7 cm s −1 , a specific but nonsaturable diffusion pathway of permeability 85·10 −7 cm s −l , and a nonspecifc passive diffusion pathway of permeability 2·10 −7 cm s −1 .