TRANSEPITHELIAL TRANSPORT OF TAURINE ACROSS ISOLATED BOVINE RETINAL PIGMENT EPITHELIUM

Abstract

Abstract: : Purpose: To measure transepithelial transport of taurine (TT) across isolated bovine retinal pigment epithelium (RPE) modelling in–vivo light evoked changes of subretinal potassium concentration.Methods: Isolated specimens of bovine non–tapetal RPE–Bruch's–choroid (n=21, age<3 years) were mounted in modified Ussing chambers in Krebs' buffer. RPE–viability was monitored by recording transepithelial voltage and resistance. Movement of taurine over a period of 2 hours was measured across bovine RPE–Bruch's–choroid by high–performance liquid chromatography (HPLC) and radio–labelling. A high substrate concentration of 10 mM to saturate both high and low affinity taurine carriers and a low substrate concentration of 50 µM to model plasma taurine levels was used. Taurine flux was measured with potassium concentrations at the apical side of 6 mM and 2.2 mM. Results: TT was linear with time in all experiments. At a physiological substrate concentration of 50 µM TT in the choroid–retina direction was 158.5 and 101.1 pmol/4mm/hr at 6 mM and 2.2 mM apical potassium concentration. TT at 10 mM substrate concentration in the choroid–retina direction was 33.96 and 26.2 nmol/4mm/hr at 6 mM and 2.2 mM apical potassium concentration. TT at 10mM substrate concentration in the retina–choroid direction was 39.71 and 19.25 nmol/4mm/hr at 6 mM and 2.2 mM apical potassium concentration.Conclusion: TT across bovine RPE is linear with time. Direction of TT is of similar magnitude in both directions depending on apical and basolateral substrate concentrations. The transport rate depends on light evoked changes of the subretinal potassium concentration. These results give an indication of TT across the RPE at carrier–saturated and physiological taurine levels and may be valuable for future evaluation of RPE–transport function in in–vitro models of RPE disease.

Keywords: retinal pigment epithelium • taurine