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Title: Substrate regulation of ascorbate transport activity in astrocytes

Astrocytes possess a concentrative L-ascorbate (vitamin C) uptake mechanism involving a Na(+)-dependent L-ascorbate transporter located in the plasma membrane. The present experiments examined the effects of deprivation and supplementation of extracellular L-ascorbate on the activity of this transport system. Initial rates of L-ascorbate uptake were measured by incubating primary cultures of rat astrocytes with L-(14C)ascorbate for 1 min at 37 degrees C. We observed that the apparent maximal rate of uptake (Vmax) increased rapidly (less than 1 h) when cultured cells were deprived of L-ascorbate. In contrast, there was no change in the apparent affinity of the transport system for L-(14C)ascorbate. The increase in Vmax was reversed by addition of L-ascorbate, but not D-isoascorbate, to the medium. The effects of external ascorbate on ascorbate transport activity were specific in that preincubation of cultures with L-ascorbate did not affect uptake of 2-deoxy-D-(3H(G))glucose. We conclude that the astroglial ascorbate transport system is modulated by changes in substrate availability. Regulation of transport activity may play a role in intracellular ascorbate homeostasis by compensating for regional differences and temporal fluctuations in external ascorbate levels.
Authors:
; ; ;  [1]
  1. (Univ. of Western Ontario, London (Canada))
Publication Date:
OSTI Identifier:
5962553
Resource Type:
Journal Article
Resource Relation:
Journal Name: Neurochemical Research; (USA); Journal Volume: 15:10
Country of Publication:
United States
Language:
English
Subject:
59 BASIC BIOLOGICAL SCIENCES; ASCORBIC ACID; MEMBRANE TRANSPORT; GLUCOSE; SUBSTRATES; BIOLOGICAL AVAILABILITY; CARBON 14 COMPOUNDS; CELL MEMBRANES; CEREBRAL CORTEX; HOMEOSTASIS; NERVE CELLS; RATS; TRACER TECHNIQUES; TRITIUM COMPOUNDS; ALDEHYDES; ANIMAL CELLS; ANIMALS; BODY; BRAIN; CARBOHYDRATES; CELL CONSTITUENTS; CENTRAL NERVOUS SYSTEM; CEREBRUM; HEXOSES; HYDROGEN COMPOUNDS; ISOTOPE APPLICATIONS; LABELLED COMPOUNDS; MAMMALS; MEMBRANES; MONOSACCHARIDES; NERVOUS SYSTEM; ORGANIC COMPOUNDS; ORGANS; RODENTS; SACCHARIDES; SOMATIC CELLS; VERTEBRATES; VITAMINS 550201* -- Biochemistry-- Tracer Techniques