Effect of Taurine and Apical Potassium Concentration on Electrophysiologic Parameters of Bovine Retinal Pigment Epithelium

Abstract

Abstract: : Purpose: To assess the effect of taurine and apical potassium concentration modelling in–vivo light evoked changes on the transepithelial potential (TEP) and the transepithelial resistance (TER) of isolated bovine retinal pigment epithelium (RPE). Methods: Isolated specimens of bovine non–tapetal RPE–Bruch's–choroid (RPE–BC) were mounted in modified Ussing chambers. The apical and the basolateral side of the preparations were exposed to 10 mM and 10 µM concentrations of taurine in Krebs' medium with either 6.04 mM or 2.2 mM potassium in the apical compartment. TEP and TER were recorded over 120 minutes. Results: TEP and TER decreased with exposure to taurine on the apical or on the basolateral side over the course of one hour followed by a recovery towards baseline. The degree of this response did not depend on the concentration of taurine but was more pronounced when taurine was added to the apical compartment. Lowering apical potassium from 6.04 mM to 2.2 mM further pronounced the decrease of TEP and TER. Conclusions: Light–induced release of taurine from the outer retina and light–induced decrease of the potassium concentration in the subretinal space synergistically lead to a temporary decrease in TEP and TER. Thereby, taurine uptake into the RPE is reduced probably by a reduction of the activity of the electrogenic Na⁺/taurine co–transporter of the apical RPE cell membrane. Our findings suggest that via this mechanism taurine as a protection of photoreceptor outer segments from oxidative stress remains longer in the subretinal space following exposure to light.

Keywords: taurine • retinal pigment epithelium • electrophysiology: non-clinical