In vitro polarized transport of L-phenylalanine in human nasal epithelium and partial characterization of the amino acid transporters involved.
OBJECTIVE
The purpose of this study was to provide functional and molecular evidence to support the existence of large neutral amino acid transporters in human nasal epithelium using nasal primary cell culture model.


METHODS
L-Phenylalanine was used as a model substrate to characterize carrier-mediated permeation of amino acids across human nasal epithelium. The influence of temperature, concentration, other amino acids, metabolic/transport inhibitors, and polarity/stereo-selectivity on transport of the model compound was investigated. Reverse transcriptase polymerase chain reaction was used for molecular characterization of the existence of the transporters.


RESULTS
The transport of L-phenylalanine across the human nasal epithelium was polarized (apical --> basolateral >> basolateral --> apical), saturable (Km = 1.23 mM; Vmax = 805.1 nmol/mg protein/min) and stereo-selective (permeation of L-phenylalanine >> D-Phenylalanine). Its permeation was significantly (< 0.05) reduced by cationic, small and large neutral amino acids, oubain, amiloride, sodium-free medium, and temperature lowering. Reverse transcriptase polymerase chain reaction revealed the presence of the broad-scope cationic-dependent amino acid transporter gene (y+LAT-2) in the human nasal epithelium.


CONCLUSIONS
Based on the results of this study, one may postulate that the human nasal epithelium expresses L-amino acid transporters. More studies are necessary for detailed characterization of the transporters.
Agu
Remigius
R
Laboratory for Pharmacotechnology and Biopharmacy, K.U. Leuven, Campus Gasthuisberg O&N, Herestraat 49, B-3000 Leuven, Belgium.
Dang
Hoang Vu
HV
Jorissen
Mark
M
Willems
Tom
T
Vandoninck
Sandy
S
Van Lint
Johan
J
Vandenheede
Jackie V
JV
Kinget
Renaat
R
Verbeke
Norbert
N
D026905:Amino Acid Transport Systems / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active; D002478:Cells, Cultured; D006801:Humans; D009297:Nasal Mucosa / Q000378:metabolism*; D010649:Phenylalanine / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013696:Temperature
D026905:Amino Acid Transport Systems; D012333:RNA, Messenger; D010649:Phenylalanine