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Ascorbic Acid Uptake by a High‐Affinity Sodium‐Dependent Mechanism in Cultured Rat Astrocytes
Author(s) -
Wilson John X.
Publication year - 1989
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1989.tb07396.x
Subject(s) - ascorbic acid , extracellular , ouabain , biochemistry , intracellular , chemistry , sodium , biophysics , biology , food science , organic chemistry
Ascorbic acid (vitamin C) is synthesized in rodent liver, circulates in the blood, and is concentrated in the brain. Experiments were performed to characterize the mechanism of ascorbate uptake by rat cerebral astrocytes in primary culture. Astroglial uptake of L‐[ l4 C]ascorbate was observed to be both saturable and stereoselective. In addition, uptake was dependent on both the incubation temperature and the concentration of Na + because it was largely inhibited by cooling to 4°C, by treatment with ouabain to increase intracellular Na + , and by the substitution of K + , Li + , or N‐methyl‐D‐glu‐camine for extracellular Na + . The affinity for ascorbate was relatively high in cells incubated with a physiological concentration of extracellular Na + , because the apparent K m was 32 μ M in 138 m M Na + . However, the affinity for ascorbate was significantly decreased when the extracellular Na + concentration was lowered. Treatment of astrocytes with dibu‐tyryl cyclic AMP induced stellation and increased the maximum rate of ascorbate uptake by 53%. We conclude that astrocytes possess a stereoselective, high‐affinity, and Na + ‐dependent uptake system for ascorbate. This system may regulate the cerebral ascorbate concentration and consequently modulate neuronal function.