AJP - Endocrinology and Metabolism, Vol 243, Issue 4 272-E277, Copyright © 1982 by American Physiological Society
Transport of alpha-keto analogues of amino acids across blood-brain barrier in rats
A. R. Conn and R. D. Steele
The transport of 14C-labeled alpha-keto acids across the blood-brain
barrier (BBB) was studied in rats anesthetized with sodium pentobarbital
using a modification of a single-injection dual-isotope technique.
alpha-Keto acids were found to cross the BBB via a saturable
carrier-mediated transport system that may be specific based on lack of
inhibition by glucose, isoleucine, and ketone bodies on the uptake of
tracer levels of 14C-labeled alpha-keto acids. alpha-Ketobutyrate and
alpha-keto-gamma-methiolbutyrate, both straight chain keto acids, and
alpha-ketoisocaproate, a branched-chain keto acid, appeared to cross the
barrier by a common carrier based on cross-inhibition studies. Aromatic
keto acids had no effect on the uptake of tracer levels of these 14C-keto
acids. The Km of transport of alpha-ketobutyrate, alpha-ketoisocaproate,
and alpha-keto-gamma-methiolbutyrate, was 0.11, 0.60, and 0.33 mM,
respectively. The corresponding Vmax was 15.7, 73.3, and 30.2 nmol . g-1 .
min-1. Phenylpyruvate was found not to cross the BBB. Inhibition of brain
uptake of alpha-keto acids by propionate and pyruvate, and not by
DL-beta-hydroxybutyrate suggests that alpha-keto acids and monocarboxylic
acids are transported either via a common system independent of ketone
bodies or share an affinity with a monocarboxylic acid and an alpha-keto
acid transport system.
