Department of Pharmaceutics, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama.
Biol Pharm Bull. 2020;43(8):1241-1247. doi: 10.1248/bpb.b20-00290.
Retinal pigment epithelial (RPE) cells form the outer blood-retinal barrier (BRB) and regulate drug/compound exchange between the neural retina and blood in the fenestrated blood vessels of retinal choroid via membrane transporters. Recent studies have elucidated that RPE cells express hemichannels, which are opened by extracellular Ca depletion and accept several drugs/compounds as a transporting substrate. The objective of this study was to elucidate the hemichannel-mediated compound transport properties of the outer BRB. In human RPE cells, namely ARPE-19 cells, time-dependent uptake of fluorescent hemichannel substrates, such as Lucifer Yellow, sulforhodamine-101 (SR-101), and propidium iodide (PI) was promoted under Ca-depleted conditions. The uptake of these substrates under Ca-depleted conditions exhibited saturable kinetics with a Michaelis-Menten constant (K) of 87-109 µM. In addition, SR-101 and PI uptake by ARPE-19 cells was dependent of extracellular Ca concentration, and that under Ca-depleted conditions was significantly decreased by typical substrates and/or inhibitors for hemichannels. Moreover, Ca-depleted conditions promoted the efflux transport of calcein from ARPE-19 cells, and the promoted calcein efflux transport was significantly inhibited by a typical hemichannel inhibitor. These results suggested that hemichannels at the outer BRB were involved in the influx and efflux transport of drugs/compounds.
视网膜色素上皮 (RPE) 细胞形成了外血视网膜屏障 (BRB)，并通过膜转运体调节神经视网膜和脉络膜有孔血管中血液之间的药物/化合物交换。最近的研究已经阐明，RPE 细胞表达连接子通道，该通道在外钙耗竭的情况下被打开，并接受几种药物/化合物作为转运底物。本研究的目的是阐明外 BRB 的连接子通道介导的化合物转运特性。在人 RPE 细胞（即 ARPE-19 细胞）中，在钙耗竭条件下，荧光连接子通道底物，如 Lucifer Yellow、sulforhodamine-101 (SR-101) 和碘化丙啶 (PI) 的时间依赖性摄取得到促进。这些底物在钙耗竭条件下的摄取表现出米氏常数 (K) 为 87-109 μM 的饱和动力学。此外，SR-101 和 PI 通过 ARPE-19 细胞的摄取依赖于细胞外钙浓度，并且在钙耗竭条件下，典型的连接子通道底物和/或抑制剂显著降低了摄取。此外，钙耗竭条件促进了 ARPE-19 细胞中 calcein 的外排转运，而典型的连接子通道抑制剂显著抑制了促进的 calcein 外排转运。这些结果表明，外 BRB 的连接子通道参与了药物/化合物的内流和外排转运。
