Ascorbic acid in human neutrophils.
The uptake and distribution of ascorbic acid and the effect of extracellular glucose on ascorbic acid transport were investigated in human neutrophils. Freshly isolated neutrophils contained 1.0-1.4 mmol ascorbic acid/L, at least 94% of which was present unbound in the cytosol. Intracellular ascorbic acid was found only in the reduced form. The presence of physiologic amounts of ascorbic acid in the extracellular buffer led to the accumulation of millimolar concentrations of ascorbic acid intracellularly. Accumulation was mediated by a high- and a low-affinity transport activity. The high-affinity transport activity had an apparent Km of 2-5 mumol/L whereas the low-affinity transport activity had an apparent Km of 6-7 mmol/L. Glucose inhibited the uptake and accumulation of ascorbic acid by both transport activities in a concentration-dependent fashion. Glucose-induced inhibition of both ascorbic acid transport activities was completely reversible.
Washko
P
P
Laboratory of Cell Biology and Genetics, National Institute of Diabetes, Digestive, and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Rotrosen
D
D
Levine
M
M
D001205:Ascorbic Acid / Q000378:metabolism* / Q000493:pharmacokinetics; D001692:Biological Transport; D003683:Dehydroascorbic Acid / Q000378:metabolism; D005110:Extracellular Space / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D009504:Neutrophils / Q000378:metabolism*; D009994:Osmolar Concentration; D012044:Regression Analysis; D013696:Temperature; D013997:Time Factors; D014018:Tissue Distribution
D005947:Glucose; D001205:Ascorbic Acid; D003683:Dehydroascorbic Acid