Identification and characterization of the glucose transporter of the blood-brain barrier by cytochalasin B binding and immunological reactivity.

3HCytochalasin B was used as a ligand to identify and characterize the glucose transporter in cerebral microvessels of the rat and the pig. Specific cytochalasin B binding, defined as that fraction of the total binding that is stereospecifically displaced by excess (500 mM) D-glucose, is saturable. Kinetic studies of this specific binding to cerebral microvessel preparations showed a dissociation constant (Kd) of 0.65-0.88 microM and a maximal binding (Bmax) of 60-80 pmol/mg of protein. In comparison, the Bmax of particulate fractions of the cerebral cortex was about one-tenth that of cerebral microvessels. The ability of various hexoses to displace specific cytochalasin B binding to cerebral microvessels in vitro correlated well with the capability of these hexoses to cross the blood-brain barrier in vivo. Irreversible photoaffinity labeling of the glucose transporter of cerebral microvessels with cytochalasin B followed by solubilization and polyacrylamide gel electrophoresis labeled a polypeptide(s) with a molecular weight of about 53,000. Antibodies prepared against the glucose transporter of human erythrocytes also reacted with a polypeptide(s) with a molecular weight of about 53,000 on electrophoresed preparations of cerebral microvessels. These results indicate that cerebral microvessels are richly endowed with a glucose transporter moiety of similar molecular weight and antigenic characteristics as the glucose transporter of human erythrocytes and other mammalian tissues.