INHIBITION PATTERN BY ANALOGS INDICATES THE PRESENCE OF TEN OR MORE TRANSPORT-SYSTEMS FOR AMINO-ACIDS IN BRAIN-CELLS

Abstract— We surveyed the transport systems present in the brain for amino acids. Cellular transport was measured in brain slices, and capillary transport was estimated by measuring in vivo the short‐term (15 s) extraction by brain from the blood. Specific analog inhibition of uptake was used to distinguish the classes. Amino acid levels (close to physiological) were such that primarily the ‘low‐affinity’ transport was measured. In brain tissue we could distinguish 10 overlapping amino acid transport classes. Five of these, described in a number of tissues, were characterized by their substrates: alanine (A system), leucine (L system), alanine‐serine‐cysteine (ASC system), glutamic acid (Glu system), and arginine (Ly+ system), respectively. The others distinguished were each fairly specific for one of the following five amino acids: glycine, proline, γ‐aminobutyric acid (GABA), taurine, and lysine. Of these 10 systems only 4 could be clearly found in capillary transport: L, ASC, Ly +, and Glu. The properties and the distribution of the transport systems are different. Examples are that at least one of the systems is present primarily only in neurons (GABA), and one primarily in glia (taurine). The specificity of some of the systems, e.g. A, is altered during development. In contrast to the properties of most other systems, there is little Na+, energy, or temperature dependence of the L system. This is reflected in the properties of capillary neutral amino acid transport when the L system is the predominant one. Copyright © 1979, Wiley Blackwell. All rights reserved