Passive and carrier mediated glucose transport across ocular barriers and via intraocular epithelia in normal and streptozotocin (SZ)-diabetic animals will be studied to determine the role of insulin deficiency and hyperglycemia in the diabetic eye. In vivo kinetic studies have shown that blood-aqueous and vitreous passive (14C)-L-glucose rate constants increase within 10 days post-SZ, whereas, carrier facilitated (3H)-m-D-glucose is decreased only later (50 + days). Preliminary studies with the guinea pig (a mammalian model lacking a retinal circulation) have provided in vivo evidence suggesting that the retinal pigment epithelium (RPE) is an anatomical locus for carrier facilitation of glucose transport. Proposed in vivo studies using various sized molecular probes are designed to explore the nature of the blood-ocular diabetic passive leak in an effort aimed at correlating vitreous fluorescein studies with our SZ-diabetic studies using glucose analogs. Other in vivo studies will test vitamin E, C and Pfizer's Sorbinil usefullness in preventing the diabetic and transport changes seen. We have previously reported on in vivo glucose transport into lens and cornea of the rat and propose to extend these studies to diabetic animals. This would clarify whether glucose transport into lens and cornea is impaired in the diabetic animal. Our in vivo kinetic modelling will be expanded so that reversible transport occurs between blood-retina-vitreous compartments. In vitro studies of chamber mounted frog RPE have resulted in publications on ion transport and glucose transport. Glucose transport across the frog RPE was found to be insulin insensitive, adversely affected by elevated concentrations of glucose and not dependent on an immediate ATP energy supply or functioning ion-transport system. New studies include: mechanisms of amino acid transport with special attention to roles played by insulin and ascorbic acid, and an explorative study of pharmacology of ion and glucose transport across bullfrog RPE. Recent work with cell suspensions of bullfrog RPE have indicated carrier mediation of glucose transport not insulin dependent. This work will be extended to include RPE cells from diabetic animals aimed at studying the kinetics of glucose transport in specific diabetic cell populations. Specific binding studies with (125I)-Insulin have revealed that although insulin is not required for carrier glucose transport a specific insulin receptor is present in frog RPE membrane. Binding studies will be extended to include epithelial cells isolated from normal and diabetic rats and guinea pigs.
