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Characterization of Ascorbic Acid Uptake by Isolated Rat Kidney Cells^1,2,

Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322

Isolated kidney cells accumulated L[1-¹⁴C]ascorbic acid in a time-dependent manner and reached a steady state after 15 min at 37°C. Initial velocity for uptake was over 300 pmol/mg protein per min when cells were separated from the bathing solution using a density gradient established during centrifugation. The uptake process was saturable with an apparent concentration at half maximal uptake of 36 µmol/L. Ascorbate uptake was reduced by metabolic inhibitors and was temperature dependent. Although ascorbic acid is an acid anion at pH 7.4, uptake did not appear to be inhibited by other acid anions such as p-aminohippurate and probenecid; however, involvement of the ion gradient established by Na⁺,H⁺-adenosine triphosphatase could not be confirmed. Replacing the sodium ion with other monovalent ions reduced the accumulation of ascorbate significantly. Isoascorbic and dehydroascorbic acids inhibited ascorbate uptake (34 and 13 mmol/L, respectively), whereas high concentrations of glucose showed some stimulation. These findings indicated that ascorbic acid is reabsorbed by the kidney in a sodium-dependent active transport process that is not common to other acid anions and has some specificity for the ascorbic acid structure.

KEY WORDS: • ascorbic acid • ultamin C • biological transport • kidney • rats • uptake

¹ Presented in part at the 1990 Annual Meeting of the Federation of American Societies for Experimental Biology, April 1990, Washington, DC. [Bowers-Komro, D. M. and McCormick, D. B. (1990) Characterization of ascorbic acid uptake by renal tubular epithelial cells. FASEB J. Vol. 4, No. 3 (abs. 1634)]

² Supported in part by Research Contract Number 89042 from the State of Florida Department of Citrus.

³ To whom all correspondence should be addressed.

Manuscript received 22 March 1990. Revision accepted 20 July 1990.

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