title: Role of PEPT2 in the choroid plexus uptake of glycylsarcosine and 5-aminolevulinic acid: studies in wild-type and null mice.
abstract: OBJECTIVE
  To determine the importance of PEPT2 in the uptake of glycylsarcosine (GlySar) and 5-aminolevulinic acid (5-ALA) in mouse choroid plexus whole tissue.
  
  
  METHODS
  Uptake studies were performed in bicarbonate artificial cerebrospinal fluid buffer using choroid plexuses isolated from PEPT2+/+ and PEPT2-/- mice. [14C]GlySar and [14C]5-ALA were studied as a function of temperature, concentration, potential inhibitors, and low sodium conditions.
  
  
  RESULTS
  PEPT2-/- mice exhibited a 90% reduction in GlySar uptake (p < 0.001) and a 92% reduction in 5-ALA uptake (p < 0.001) as compared to wild type animals. At 4 degrees C (vs. 37 degrees C), GlySar uptake was reduced by 95% in PEPT2+/+ mice; no difference was observed in null animals. Unlabeled GlySar inhibited the uptake of [14C]GlySar in PEPT2+/+ mice (p < 0.01); self-inhibition did not occur in PEPT2-/- mice. GlySar demonstrated saturable uptake in PEPT2+/+ mice (Vmax = 16.4 pmol mg(-1) min(-1), Km = 70 microM, Kd = 0.014 microl mg(-1) min(-1)), however, uptake was linear in PEPT2-/- mice (Kd = 0.023 microl mg(-1) min(-1)). Low sodium buffer (1 mM) resulted in 75% and 59% reductions, respectively, in GlySar (p < 0.001) and 5-ALA (p < 0.01) uptake in PEPT2+/+ mice; no differences were observed in PEPT2-/- mice. Overall, about 90-95% of the choroid plexus uptake of GlySar and 5-ALA was mediated by PEPT2, with about 5-10% of the residual uptake occurring by nonspecific mechanisms.
  
  
  CONCLUSIONS
  The results demonstrate that PEPT2 is the only transporter responsible for the choroid plexus uptake of GlySar and 5-ALA. They also suggest a role for PEPT2 in the clearance of dipeptides and endogenous peptidomimetics from cerebrospinal fluid.
authors.affiliation: Department of Pharmaceutical Sciences, The University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: Scott M
authors.initials: SM
authors.lastname: Ocheltree
authors.forename: Hong
authors.initials: H
authors.lastname: Shen
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Hu
authors.forename: Jianming
authors.initials: J
authors.lastname: Xiang
authors.forename: Richard F
authors.initials: RF
authors.lastname: Keep
authors.forename: David E
authors.initials: DE
authors.lastname: Smith
mesh_terms: D000622:Aminolevulinic Acid / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active; D002831:Choroid Plexus / Q000378:metabolism*; D004151:Dipeptides / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D018345:Mice, Knockout; D017319:Photosensitizing Agents / Q000378:metabolism; D027981:Symporters / Q000235:genetics / Q000502:physiology*
chemical_list: D004151:Dipeptides; D017319:Photosensitizing Agents; D027981:Symporters; C093694:hydrogen-coupled oligopeptide transporter PepT2; C004194:glycylsarcosine; D000622:Aminolevulinic Acid