gms | German Medical Science

To evaluate the relative influence of ageing on transport of taurine (TT) across Bruch's choroid (BC) and the retinal pigment epithelium (RPE).

Isolated specimens of bovine non-tapetal Bruch's choroid (n=5, age<3 years) were mounted in modified Ussing chambers in Krebs` buffer with and without RPE. RPE-viability was monitored by recording transepithelial voltage and resistance. TT over a period of 2 hours was measured across bovine Bruch's choroid with and without RPE by high-performance liquid chromatography 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. Uptake of ³H-taurine into isolated human RPE of the age group >60 years was measured. TT was measured across human BC as a function of age (13-88 years).

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 to 101.1 pmol/4mm/hr depending on the apical potassium concentration. TT across RPE-BC at 10mM substrate concentration was 33.96 nmol/4mm/hr before and 111.12 nmol/4mm/hr after removal of the RPE. TT across human BC declined linearly with age (169.8 at age 10 years to 105.9 nm/hr/4mm at age 90 years). Uptake of taurine into human RPE at a taurine concentration of 1 μM was independent of donor age (p>0.05) and averaged at 2.83 ± 0.27 (SEM) pmol/10min/6mm.

TT across bovine BC is in excess of TT across bovine RPE. TT across human BC declines linearly with age but remains in excess of the calculated demand of aged human RPE. These results give an indication of the relative impact of ageing on the individual compartments (BC and the RPE) of the transport pathway of taurine between the choroidal blood supply and the outer retina.