title: PEPT2-mediated transport of 5-aminolevulinic acid and carnosine in astrocytes.
abstract: 5-aminolevulinic acid (ALA) and carnosine have important physiological and pathophysiological roles in the CNS. Both are substrates for the proton-coupled oligopeptide transporter PEPT2. The purpose of the current study was to determine the importance of PEPT2 in the uptake of ALA and carnosine in rat and mouse (PEPT2+/+ and PEPT2-/-) cultured neonatal astrocytes. Although neonatal astrocytes are known to express PEPT2, its quantitative importance in the transport of these compounds is not known. [14C]ALA uptake in neonatal rat astrocytes was inhibited by dipeptides, an alpha-amino containing cephalosporin (which is a PEPT2 substrate) but was not affected by a non-amino containing cephalosporin (which is not a PEPT2 substrate). Uptake was pH sensitive as expected from a proton-coupled transporter and was saturable (Vmax=715+/-29 pmol/mg/min, Km=606+/-14 microM). [3H]Carnosine uptake in neonatal rat astrocytes was inhibited by dipeptides but not by histidine (a substrate for the peptide/histidine transporters PHT1 and PHT2) and also showed saturable transport (Vmax=447+/-23 pmol/mg/min, Km=43+/-5.5 microM). Neonatal astrocytes from PEPT2-/- mice had a 62% reduction in [14C]ALA uptake and a 92% reduction in [3H]carnosine uptake compared to PEPT2+/+ mice. These results demonstrate that PEPT2 is the primary transporter responsible for the astrocytic uptake of ALA and carnosine.
authors.affiliation: Department of Neurosurgery, University of Michigan, 5014 BSRB, Ann Arbor, MI 48109-2200, USA. jmxxdrnx@umich.edu
authors.forename: Jianming
authors.initials: J
authors.lastname: Xiang
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Hu
authors.forename: David E
authors.initials: DE
authors.lastname: Smith
authors.forename: Richard F
authors.initials: RF
authors.lastname: Keep
mesh_terms: D000622:Aminolevulinic Acid / Q000378:metabolism*; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects / Q000502:physiology; D002336:Carnosine / Q000378:metabolism*; D002478:Cells, Cultured; D002490:Central Nervous System / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D002511:Cephalosporins / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D051381:Rats; D017207:Rats, Sprague-Dawley; D027981:Symporters / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*
chemical_list: D000963:Antimetabolites; D002511:Cephalosporins; D027981:Symporters; C093694:hydrogen-coupled oligopeptide transporter PepT2; D000622:Aminolevulinic Acid; D002336:Carnosine