Fujita T, Kishida T, Okada N, Ganapathy V, Leibach F H, Yamamoto A
Department of Biopharmaceutical Sciences, Kyoto Pharmaceutical University, Japan.
Neurosci Lett. 1999 Aug 20;271(2):117-20. doi: 10.1016/s0304-3940(99)00540-6.
High-affinity type H+/peptide cotransporter PEPT2 is preferentially expressed in the kidney, and is responsible for reabsorption of di- and tripeptides in epithelial tubules. Interestingly, PEPT2 has been recently cloned from rat brain. However, there is very little information available on the peptide transporter activity in the brain. In the present study, we investigated the interaction of kyotorphin (L-tyrosyl-L-arginine) with the peptide transporter using synaptosomes prepared from rat cerebellum. The activity of the peptide transporter was assessed by measuring the uptake of radiolabeled glycyl-sarcosine (Gly-Sar), which is a prototypical substrate for the peptide transporter, in the presence of H+-gradient. Kyotorphin competitively inhibited the uptake of Gly-Sar with an inhibitory constant (Ki) of 30 +/- 4 microM in rat cerebellum synaptosomes. This uptake property is very close to that of PEPT2. Carnosine (beta-alanyl-L-histidine) also inhibited the uptake of Gly-Sar, on the other hand, TRH did not interact with the peptide transporter. RT-PCR using specific primers revealed that PEPT2 mRNA exists in cerebellum in rat. Taken collectively, these results indicate that the functional peptide transport system in rat cerebellum might be the high affinity transporter PEPT2.
高亲和力的H⁺/肽共转运体PEPT2优先表达于肾脏，负责上皮小管中二肽和三肽的重吸收。有趣的是，PEPT2最近已从大鼠脑中克隆出来。然而，关于脑内肽转运体活性的信息非常少。在本研究中，我们使用从大鼠小脑制备的突触体研究了脑啡肽（L-酪氨酰-L-精氨酸）与肽转运体的相互作用。肽转运体的活性通过在存在H⁺梯度的情况下测量放射性标记的甘氨酰肌氨酸（Gly-Sar）的摄取来评估，Gly-Sar是肽转运体的典型底物。脑啡肽在大鼠小脑突触体中竞争性抑制Gly-Sar的摄取，抑制常数（Ki）为30±4μM。这种摄取特性与PEPT2非常接近。另一方面，肌肽（β-丙氨酰-L-组氨酸）也抑制Gly-Sar的摄取，而促甲状腺激素释放激素（TRH）不与肽转运体相互作用。使用特异性引物的RT-PCR显示大鼠小脑中存在PEPT2 mRNA。综上所述，这些结果表明大鼠小脑中的功能性肽转运系统可能是高亲和力转运体PEPT2。
