Mechanism of ganciclovir uptake by rabbit retina and human retinal pigmented epithelium cell line ARPE-19

Abstract

Purpose. The objective of this study was to elucidate the mechanism of ganciclovir uptake by the rabbit retina and the human retinal pigmented epithelium cell line ARPE-19.Materials and methods. [3H]Adenine, [3H]adenosine, [3H]thymidine, and [3H]ganciclovir were used to elucidate the mechanism of ganciclovir uptake by the ARPE-19 cell line and the isolated rabbit retinal tissue. Uptake studies using ARPE-19 cell line and isolated rabbit retina were carried out at 37°C and 25°C, respectively, for 5 min.Results. Uptake of [3H]adenine by ARPE-19 cells decreased by 95% in the presence of unlabeled adenine. Other nucleobases such as guanine, thymine, and uracil and the nucleosides adenosine, guanosine, thymidine, uridine, and inosine also reduced uptake of [3H]adenine by the ARPE-19 cells. Although [3H]adenosine and [3H]thymidine uptake was inhibited by nucleosides, nucleobases did not demonstrate any inhibitory effect, indicating that nucleosides can only bind to the nucleobase transporter but are not translocated by it. Uptake of the nucleosides and nucleobases by the ARPE-19 cells was sodium and pH independent. [3H]adenosine and [3H]thymidine uptake by the ARPE-19 cells was inhibited by nanomolar quantities of nitrobenzylthioinosine. Uptake of [3H]adenine by the isolated rabbit retina was drastically reduced in the presence of unlabeled adenine. Unlabeled thymidine and guanosine, and removal of sodium from the uptake medium, inhibited uptake of [3H]thymidine by the rabbit retina. Nucleosides, nucleobases, and unlabeled ganciclovir did not exhibit any inhibitory effect on [3H]ganciclovir uptake by the isolated rabbit retina or ARPE-19 cells.Conclusions. Our results indicate that although the rabbit retina and the ARPE-19 cell line express nucleoside and nucleobase transporters, translocation of ganciclovir does not involve any carrier-mediated transport process. Rather, ganciclovir uptake by the rabbit retina and ARPE-19 cells is governed primarily by passive diffusion.