Abstract
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-α-amino cephalosporins (cephaloridine, cephalothin). In contrast, di- and tripeptides (GlySar, glycylproline, glycylglycylhistidine), neuropeptides (carnosine), and α-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.
Footnotes
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Send reprint requests to: David E. Smith, Ph.D., 4302A Upjohn Center, 1310 E. Catherine St., The University of Michigan, Ann Arbor, MI 48109-0504. E-mail: smithb{at}umich.edu
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↵1 This study was supported in part by Grants R01 GM35498 (to D.E.S.) and R01 NS34709 and P01 HL18575 (to R.F.K.) from the National Institutes of Health.
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↵2 A.N. was a Research Fellow from the Department of Neurosurgery, Klinikum Grosshadren, Ludwig-Maximilians-University, Munich, Germany.
- Abbreviations:
- PHT1
- peptide/histidine transporter
- TAG
- Tyr-d-Ala-Gly
- CSF
- cerebrospinal fluid
- GlySar
- glycylsarcosine
- GlyGlyHis
- glycylglycylhistidine
- SITS
- 4-acetamido-4′-isothiocyanatostilbene-2,2′-disulfonic acid
- TEA
- tetraethylammonium
- aCSF
- artificial CSF
- MES
- 2-(N-morpholino)ethanesulfonic acid
- Received March 16, 2000.
- Accepted May 4, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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