Get access

TRANSPORT OF SUGARS INTO MICROVESSELS ISOLATED FROM RAT BRAIN: A MODEL FOR THE BLOOD-BRAIN BARRIER1

Authors

  • Alan R. Kolber,

    1. Biological Sciences Research Center, Department of Biochemistry and Nutrition, and Department of Pathology, University of North Carolina, Chapel Hill, NC 27514, U.S.A.
    Search for more papers by this author
    • 2

      Research Triangle Institute, Research Triangle Park, NC 27709, U.S.A.

  • C. Robert Bagnell,

    1. Biological Sciences Research Center, Department of Biochemistry and Nutrition, and Department of Pathology, University of North Carolina, Chapel Hill, NC 27514, U.S.A.
    Search for more papers by this author
  • Martin R. Krigman,

    1. Biological Sciences Research Center, Department of Biochemistry and Nutrition, and Department of Pathology, University of North Carolina, Chapel Hill, NC 27514, U.S.A.
    Search for more papers by this author
  • Jean Hayward,

    Corresponding authorSearch for more papers by this author
  • Pierre Morell

    1. Biological Sciences Research Center, Department of Biochemistry and Nutrition, and Department of Pathology, University of North Carolina, Chapel Hill, NC 27514, U.S.A.
    Search for more papers by this author

  • 1

    Presented in part at the 7th Annual Meeting of the Society for Neuroscience.

Author to whom reprint requests and other communications should be directed.

Abstract

Abstract— Microvessels (primarily capillaries) were isolated from the brains of rats 25-35 days of age. This preparation was characterized by light, transmission, and scanning electron microscopy. Transmission electron microscopy revealed that the endothelial cell membranes were intact and were impermeable to horseradish peroxidase. However, scanning electron microscopy revealed that damage to the membrane occurred during isolation. The isolated microvessel preparations were metabolically competent as demonstrated by their ability to metabolize [14C]glucose.

Aliquots of microvessel preparation were incubated with radioactive non-metabolizable analogs of D-glucose at various concentrations. The kinetics of accumulation of radioactivity in the capillaries were analyzed according to a model for carrier-mediated diffusion and affinity constants for 3-O-methyl- D-glucose and 2-deoxyglucose were calculated (about 18 mM at 20°C in each case). These affinity constants are somewhat greater than that expected from whole animal experiments reported by other laboratories. This discrepancy is probably accounted for by the presence of a passive diffusion component. However, despite this complication, the primary mechanism for entry of D-glucose analogues at physiological concentrations is compatible with carrier-mediated transport since: the uptake of sugar analogs was shown to be saturable, to exhibit competition for uptake between structurally similar molecules, and to be non-concentrative. In contrast, the uptake of glycerol, mannitol, and L-glucose by isolated microvessels obeyed the kinetics of simple passive diffusion and was not saturable.

Our results are compatible with the concept that the capillary is the anatomic locus of the blood-brain barrier and that this structure contains the carrier-mediated transport system for monosaccharide penetration into brain.

Ancillary