Kinetics of ascorbate transport by cultured retinal capillary pericytes. Inhibition by glucose.
Accumulation of radioactive L-[carboxyl-14C]-ascorbic acid by cultured bovine retinal capillary pericytes was studied. Kinetic analysis of the transport showed a time-dependent, saturable system with an apparent Km of 76.0 microM and a Vmax of 42 pmole/micrograms DNA/min. A facilitated carrier diffusion process was established on the basis that the system was not sensitive to 2,4-dinitrophenol, ouabain, or reduced sodium concentration in the incubation media, and that the carrier system demonstrated stereospecificity for an ascorbate analogue, dehydroascorbate, and for sugar analogues such as alpha-D-glucose and 3-0-methyl-D-glucose (3-0-MG), but not for beta-D-fructose or L-glucose. Transport of ascorbate by cultured pericytes was insulin-insensitive. 3-0-Methyl-D-glucose inhibited ascorbate transport into pericytes in a non-competitive manner with a Ki of 22 mM. These results indicate that, in cultured retinal capillary pericytes, a common facilitated carrier diffusion system is involved in the transport of ascorbate and sugar analogues such as alpha-D-glucose or 3-0-MG.
D000818:Animals; D001205:Ascorbic Acid / Q000037:antagonists & inhibitors / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002196:Capillaries / Q000187:drug effects / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D005947:Glucose / Q000494:pharmacology; D007700:Kinetics; D012160:Retina / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
D005947:Glucose; D001205:Ascorbic Acid