title: Human erythrocyte nucleoside transporter ENT1 functions at ice-cold temperatures.
abstract: The functionality of human erythrocyte nucleoside transporter ENT1 was examined at ice-cold temperatures (ICT; measured temperature, 0.5-0.7 degrees C) using rightside-out membrane vesicles (ROVs). The uptake of uridine, an ENT1 substrate, showed saturation kinetics and was inhibited by S-(4-nitrobenzyl)-6-thioinosine (NBMPR), a specific ENT1 inhibitor, at both 23 degrees C and ICT. [3H]Uridine uptake was markedly trans-stimulated by preloading ROVs with unlabeled uridine or ribavirin, another ENT1 substrate, and the overshoot phenomenon was observed at ICT. Similarly, [3H]ribavirin uptake was markedly trans-stimulated by unlabeled ribavirin or uridine at ICT. The trans-stimulated uptake of [3H]uridine at ICT was inhibited by ENT1 inhibitors/substrates such as NBMPR, dipyridamole, adenosine, and ribavirin in a concentration-dependent manner. The inhibition of [3H]uridine uptake by NBMPR and dipyridamole at ICT was also observed in intact red blood cells. Like uridine uptake, [3H]D-glucose uptake by ROVs, which is mediated by facilitative glucose transporter GLUT1, was trans-stimulated by unlabeled D-glucose at ICT, and the overshoot phenomenon was observed. In contrast, the ability of ATP-dependent transport of 5-(and-6)-carboxy-2',7'-dichlorofluorescein via multidrug resistance-associated protein 5 in inside-out membrane vesicles disappeared at ICT. These results clearly indicate that human erythrocyte transporters such as ENT1 function even at very low temperatures near 0 degrees C. The significance of these findings in transporter research is discussed.
authors.affiliation: Department of Pharmaceutics and Therapeutics, Graduate School of Biomedical Sciences, Hiroshima University. takanom@hiroshima-u.ac.jp
authors.forename: Mikihisa
authors.initials: M
authors.lastname: Takano
authors.forename: Eri
authors.initials: E
authors.lastname: Kimura
authors.forename: Satoshi
authors.initials: S
authors.lastname: Suzuki
authors.forename: Junya
authors.initials: J
authors.lastname: Nagai
authors.forename: Ryoko
authors.initials: R
authors.lastname: Yumoto
mesh_terms: D003080:Cold Temperature; D004305:Dose-Response Relationship, Drug; D033721:Equilibrative Nucleoside Transporter 1 / Q000502:physiology*; D004910:Erythrocyte Membrane / Q000378:metabolism*; D051272:Glucose Transporter Type 1 / Q000502:physiology; D006801:Humans; D012254:Ribavirin / Q000378:metabolism; D013868:Thioinosine / Q000031:analogs & derivatives / Q000494:pharmacology; D014529:Uridine / Q000378:metabolism
chemical_list: D033721:Equilibrative Nucleoside Transporter 1; D051272:Glucose Transporter Type 1; C438649:SLC29A1 protein, human; C495677:SLC2A1 protein, human; D013868:Thioinosine; D012254:Ribavirin; C001789:4-nitrobenzylthioinosine; D014529:Uridine