AJP - Regulatory, Integrative and Comparative Physiology, Vol 258, Issue 6 1436-R1444, Copyright © 1990 by American Physiological Society
Facilitated transport of L-phenylalanine across blood-nerve barrier of rat peripheral nerve
K. C. Wadhwani, Q. R. Smith and S. I. Rapoport
Laboratory of Neurosciences, National Institute on Aging, National Institutes of Health, Bethesda, Maryland 20892.
L-Phenylalanine transport across the blood-nerve barrier was studied by
perfusing Ringer solution containing trace amounts of L-[14C]phenylalanine
and [3H]dextran (a vascular marker) through the hindlimb of an anesthetized
rat. At the end of perfusion, a segment of sciatic nerve was removed,
frozen, desheathed, and processed for radioactivity counting. The
permeability-surface area product of the blood-nerve barrier (PABNB) to
L-[14C]phenylalanine decreased from 58 +/- 9 X 10(-5) to 1.7 +/- 0.3 X
10(-5) (SE) ml.s-1.g wet wt-1, as the perfusate concentration of unlabeled
L-phenylalanine was increased to 10 mM. D-Phenylalanine had less of an
inhibitory effect on L-[14C]phenylalanine uptake than did L-phenylalanine.
PABNB did not change in the presence of 50 mM alpha-(methylamino)isobutyric
acid (MeAIB) in the perfusion medium, nor by replacing NaCl by Tris.HCl.
However, addition of 50 mM 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid
(BCH) reduced PABNB to 2.1 +/- 0.3 X 10(-5) ml.s-1.g wet wt-1 (n = 4). PA
at epiperineurial barrier (PAper) of L-[14C]phenylalanine at the
epiperineurial barrier, determined from in situ incubation, was 1.4 +/- 0.2
X 10(-5) ml.s-1.g wet wt-1 (n = 6) and was unaffected by 10 mM
L-phenylalanine concentration in the incubation medium. The results
demonstrate for the first time carrier-mediated transport system for
L-phenylalanine at the blood-nerve barrier of the rat peripheral nerve.
