Ocheltree Scott M, Shen Hong, Hu Yongjun, Xiang Jianming, Keep Richard F, Smith David E
Department of Pharmaceutical Sciences, The University of Michigan, Ann Arbor, Michigan 48109, USA.
Pharm Res. 2004 Sep;21(9):1680-5. doi: 10.1023/b:pham.0000041465.89254.05.
To determine the importance of PEPT2 in the uptake of glycylsarcosine (GlySar) and 5-aminolevulinic acid (5-ALA) in mouse choroid plexus whole tissue.
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.
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.
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.
确定肽转运体2（PEPT2）在小鼠脉络丛全组织摄取甘氨酰肌氨酸（GlySar）和5-氨基酮戊酸（5-ALA）中的重要性。
使用从PEPT2+/+和PEPT2-/-小鼠分离的脉络丛，在碳酸氢盐人工脑脊液缓冲液中进行摄取研究。研究了[14C]GlySar和[14C]5-ALA作为温度、浓度、潜在抑制剂和低钠条件的函数。
与野生型动物相比，PEPT2-/-小鼠的GlySar摄取减少了90%（p<0.001），5-ALA摄取减少了92%（p<0.001）。在4℃（与37℃相比）时，PEPT2+/+小鼠的GlySar摄取减少了95%；在基因敲除动物中未观察到差异。未标记的GlySar抑制了PEPT2+/+小鼠中[14C]GlySar的摄取（p<0.01）；PEPT2-/-小鼠未发生自我抑制。GlySar在PEPT2+/+小鼠中表现出饱和摄取（Vmax = 16.4 pmol mg(-1) min(-1)，Km = 70 microM，Kd = 0.014 microl mg(-1) min(-1)），然而，在PEPT2-/-小鼠中摄取呈线性（Kd = 0.023 microl mg(-1) min(-1)）。低钠缓冲液（1 mM）导致PEPT2+/+小鼠中GlySar（p<0.001）和5-ALA（p<0.01）摄取分别减少75%和59%；在PEPT2-/-小鼠中未观察到差异。总体而言，脉络丛对GlySar和5-ALA的摄取约90-95%由PEPT2介导，约5-10%的残余摄取通过非特异性机制发生。
结果表明，PEPT2是负责脉络丛摄取GlySar和5-ALA的唯一转运体。它们还提示PEPT2在从脑脊液清除二肽和内源性肽模拟物中起作用。
