Glucose transport in isolated mammalian pigment epithelium

Abstract

The isolated retinal pigment epithelium-choroid of sheep was studied in vitro as a single membrane mounted in a Ussing chamber. The average potential of 40 tissue preparations was 6·3 mV. In all preparations the retina (apical) side was positive with respect to the choroid (basal) side. Changes in Na⁺, K⁺, or Ca²⁺ concentration on the choroid side did not affect the tissue potential, whereas a ten-fold increase in K⁺ concentration or Ca²⁺ chelation by EGTA on the retina side decreased the potential. The potential was also decreased by 0·75 mm-phloridzin and 1·0 mm-dinitrophenol. Utilizing a glucose concentration gradient of 4 mm-choroid to 1 mm-retina side, the unidirectional glucose fluxes were found to be 883 nmol/cm² · hr choroid to retina and 222 nmol/cm² · hr retina to choroid. Both unidirectional fluxes were decreased by 65% Na⁺ replacement with choline Cl. The retina to choroid flux was also decreased by 0·75 mm-phloridzin and 1·0 mm-dinitrophenol. The sodium dependence and inhibitor effects suggest that mechanisms of glucose transport other than simple diffusion are operative in sheep retinal pigment epithelium.