The glucose transport in retinal pigment epithelium is via passive facilitated diffusion

The glucose transport across the bovine retinal pigment epithelium (RPE) wa s studied in a modified Ussing chamber. Unidirectional fluxes were recorded with radioactive tracers L-[C-14]-glucose (LG) and 3-O-methyl-D-[H-3]-gluc ose (MDG). There was no significant difference between the unidirectional M DG fluxes (retina to choroid, and choroid to retina directions) with or wit hout ouabain. The effects of two glucose transporter inhibitors, phloretin and cytochalasin B, on the glucose fluxes from choroid to retina cells were also investigated. The MDG flux was found to be inhibited by 45.5% by phlo retin (10(-4) M) and 87.4% by cytochalasin B (10(-4) M). These inhibitory c haracteristics resembled the facilitated diffusion mode of glucose transpor t. The glucose transporter protein in the plasma membrane of RPE was locate d by means of photolabeling [H-3]-cytochalasin B. The labeled plasma membra ne enriched fraction was analysed by SDS-PAGE. The glucose transporter of b ovine RPE was found to have a molecular weight range of 46-53 kDa. The mole cular weight range of this transporter protein agreed with those of facilit ated glucose transporters in other tissues indicating a molecular similarit y between them. The results indicated that the glucose transport across the RPE is via passive facilitated diffusion. (C) 1998 Elsevier Science Inc. A ll rights reserved.