Function and regulation of taurine transport at the inner blood-retinal barrier

Abstract

In the retina, taurine exerts a number of neuroprotective functions as an osmolyte and antioxidant. The purpose of the present study was to elucidate the taurine transport system(s) at the inner blood-retinal barrier (BRB). [H-3]Taurine transport at the inner BRB was characterized using in vivo integration plot analysis and a conditionally immortalized rat retinal capillary endothelial cell line (TR-iBRB2 cells). The expression of the taurine transporter (TauT) was demonstrated by RT-PCR and immunoblot analyses. The apparent influx permeability clearance of [H-3]taurinene in the rat retina was found to be 259 mu L/(min (.) g retina), supporting carrier-mediated influx transport of taurine at the BRB. [H-3]Taurine uptake by TR-iBRB2 cells was Na+-, Cl-- and concentration-dependent with a K-m of 22.2 mu M and inhibited by TauT inhibitors, such as beta-alanine and hypotaurine. RT-PCR and immunoblot analyses demonstrated that TauT is expressed in TR-iBRB2 and primary cultured human retinal endothelial cells. The uptake of [H-3]taurine and the expression of TauT mRNA in TR-iBRB2 cells increased under hypertonic conditions but decreased following pretreatment with excess taurine. In conclusion, TauT most likely mediates taurine transport and regulate taurine transport at the inner BRB. (c) 2006 Elsevier Inc. All rights reserved.