Functional characterization of folate transport in osteoclast

为了探讨载体介导的叶酸转运系统可能参与破骨细胞中甲氨蝶呤的蓄积，我们研究了从大鼠肾脏分离的溶酶体中叶酸的转运，因为溶酶体膜的功能与破骨细胞的褶皱边缘相似。结果表明，溶酶体叶酸转运发生在酸性条件下(pH 5.0~6.0)，米氏常数为0.073μM。当我们考察不同的叶酸转运蛋白抑制剂对溶酶体叶酸转运的影响时，发现抑制叶酸转运的抑制剂不同于RFc1和PCft。这些结果表明，溶酶体有一个尚未鉴定的特定的叶酸转运系统，该转运系统可能参与了甲氨蝶呤在破骨细胞中的蓄积。

In order to explore the possibility that the carrier-mediated folate transport system could be involved in the accumulation of methotrexate in osteoclasts, we examined the transport of folate in lysosomes isolated from the rat kidney, since lysosomal membrane has functional similarities of the ruffled border in osteoclasts. It was found that the lysosomal folate transport occurred at an acidic pH (pH 5.0 - 6.0), and was saturable with the Michaelis constant of 0.073 μM. When we examined the effect of various inhibitors for RFC1 (reduced folate carrier 1) and PCFT (proton-coupled folate transporter) on the lysosomal folate transport, the inhibition profile was found to be different from those of RFC1 and PCFT. These results suggest that lysosomes have a specific folate transport system, which has not been identified, and this transport system may be involved in methotrexate accumulation in osteoclasts.