In situ kinetics of glucose transport across the blood-retinal barrier in normal rats and rats with streptozocin-induced diabetes.
Glucose transport across the blood-retinal barrier (BRB) was investigated in situ by means of a modification of the single-injection technique developed for studying transport across the blood-brain barrier. A retinal uptake index was calculated from the fractional extraction for 14C-glucose divided by the fractional extraction for the 3H2O reference. The use of the Eadie-Hofstee transformation to determine the Km of carrier-mediated transport revealed at least two transport systems for the unidirectional glucose flux across the BRB. Control data showed a relatively high-affinity system with a Km of 0.24 mM and a lower affinity system with a Km of 7.81 mM. Both these transport systems have been shown to be sensitive to phloretin but not to phloridzin or acetazolamide. It has also been shown that glucose transport is uneffected by Na+ or K+ concentrations but that calcium does have a significant effect on the lower affinity transport system for glucose. We have also demonstrated that the Km values of both transport systems are significantly increased by 2 months of streptozocin-induced diabetes.
D000086:Acetazolamide / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D003921:Diabetes Mellitus, Experimental / Q000378:metabolism*; D004596:Electroretinography; D005260:Female; D005947:Glucose / Q000378:metabolism*; D007477:Ions; D007700:Kinetics; D008297:Male; D010693:Phloretin / Q000494:pharmacology; D010695:Phlorhizin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D012160:Retina / Q000378:metabolism*
D007477:Ions; D010695:Phlorhizin; D005947:Glucose; D000086:Acetazolamide; D010693:Phloretin