The Change of Taurine Transport in Variable Stress States through the Inner Blood-Retinal Barrier using In Vitro Model

Taurine is the most abundant free amino acid in the retina and transported into retina via taurine transporter (TauT) at the inner blood-retinal barrier (iBRB). In the present study, we investigated whether the taurine transport at the iBRB is regulated by oxidative stress or disease-like state in a conditionally immortalized rat retinal capillary endothelial cell line (TR-iBRB) used as an in vitro model of iBRB. First, [$^3H$]taurine uptake and efflux by TR-iBRB were regulated in the presence of extracellular $Ca^{2+}$. [$^3H$]Taurine uptake was inhibited and efflux was enhanced under $Ca^{2+}$ free condition in the cells. In addition, oxidative stress inducing agents such as tumor necrosis factor-$\alpha$ (TNF-$\alpha$), lipopolysaccharide (LPS), diethyl maleate (DEM) and glutamate increased [$^3H$]taurine uptake and decreased [$^3H$]taurine efflux in TR-iBRB cells. Whereas, 3-morpholinosydnonimine (SIN-1), which is known to NO donor decreased [$^3H$]taurine uptake. Lastly, TR-iBRB cells exposed to high glucose (25 mM) medium and the [$^3H$]taurine uptake was reduced about 20% at the condition. Also, [$^3H$]taurine uptake was decreased by cytochalasin B, which is known to glucose transport inhibitor. In conclusion, taurine transport in TR-iBRB cells is regulated diversely at extracellular $Ca^{2+}$, oxidative stress and hyperglycemic condition. It suggested that taurine would play a role as a retinal protector in diverse disease states.