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Vol. 294, Issue 2, 494-499, August 2000
College of Pharmacy and Upjohn Center for Clinical Pharmacology
(N.S.T., D.E.S.), and Department of Surgery (Neurosurgery) (A.N.,
R.F.K.), The University of Michigan, Ann Arbor, Michigan
PEPT2 expression has been established in brain and, in particular, mRNA
transcripts and PEPT2 protein have been identified in choroid plexus.
However, there is little evidence for the functional presence of this
peptide transporter in choroid plexus tissue. In this study, we
examined the in vitro uptake of a model dipeptide, glycylsarcosine
(GlySar), with whole tissue rat choroid plexus in artificial
cerebrospinal fluid. Our findings are consistent with the known
transport properties of PEPT2, including its proton dependence, lack of
sodium effect, specificity, and high substrate affinity for dipeptides.
Kinetic analysis showed saturable transport of GlySar with a Michaelis
constant (Km) of 129 ± 32 µM and a maximum velocity (Vmax) of 52.8 ± 3.6 pmol/mg/min. GlySar uptake (1.88 µM) was not inhibited by 1.0 mM
concentrations of amino acids (glycine, sarcosine,
L-histidine), organic acids and bases (4-acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic acid,
tetraethylammonium), or non-
-amino cephalosporins (cephaloridine,
cephalothin). In contrast, di- and tripeptides (GlySar, glycylproline,
glycylglycylhistidine), neuropeptides (carnosine), and
-amino
cephalosporins (cefadroxil, cephalexin) inhibited the uptake of GlySar
by 85 to 90% at 1.0 mM. These findings indicate that PEPT2 is
functionally active in choroid plexus and that it might play a role in
neuropeptide homeostasis of cerebrospinal fluid. The ability of PEPT2
to transport drugs at the choroid plexus also may be important for
future drug design, delivery, and tissue-targeting considerations.
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