Characteristics of the Large Neutral Amino Acid Transport System of Bovine Brain Microvessel Endothelial Cell Monolayers

Abstract

The large neutral amino acid (LNAA) transport system, or L (leucine) system, in primary cultures of bovine brain microvessel endothelial cell monolayers has been characterized. The transendothelial transport of leucine in this in vitro blood-brain barrier (BBB) model was determined to be bidirectional and time, temperature, and concentration dependent. Leucine transport was saturable, and the apparent K_m and V_max were determined to be 0.18 mM and 6.3 nmol/mg/min, respectively. Transendothelial transport of leucine was resistant to inhibition by ouabain and sodium azide. Other LNAAs, including the centrally acting drugs α-methyl-3,4-dihydroxyphenylalanine (α-methyldopa), l-3,4-dihydroxyphenyl alanine (l-DOPA), α-methyltyrosine, and baclofen, inhibited leucine transport. The leucine carrier system was also found to be stereospecific. Sucrose, used as a diffusion marker, moved across the monolayers slowly, and its concentration was not significant for at least 30 min.