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Journal of Lipid Research, Vol. 41, 1841-1848, November 2000
Copyright © 2000 by Lipid Research, Inc.

Original Article

Functional expression of a high affinity mammalian hepatic choline/organic cation transporter

Correspondence to: Richard M. Green

Uptake by the liver of the organic cation and essential nutrient choline is required for the hepatic synthesis of phosphatidylcholine. Uptake of other organic cations is also important for the metabolism and secretion of numerous endobiotics and drugs. Although a high affinity mammalian hepatic choline transporter has been kinetically defined, it has not been previously identified. We have developed stable transfectants of BALB/3T3 cells, using a murine member of the organic cation transporter gene family (mOct1/Slc22a1), and used these cells to characterize the transport of the organic cation choline and model organic cation tetraethylammonium (TEA). Functional expression of mOct1/Slc22a1 in BALB/3T3 cells confers the saturable, temperature-dependent uptake of choline with a K_m of 42 µM, and uptake of TEA with a K_m of 43 µM. We subsequently used our cell culture uptake system to kinetically define in HepG2 cells a high affinity choline uptake process, which transports choline with a K_m similar to that of mOct1/Slc22a1 protein. We also demonstrated that organic cation transport by mOct1/Slc22a1 is inhibited by several organic cations, and that the gene is expressed in the perinatal period, at a time when phosphatidylcholine synthesis increases.

We conclude that mOct1/Slc22a1 encodes a high affinity mammalian hepatic choline/organic cation transporter. This transporter may be important for hepatic phosphatidylcholine synthesis, and for the metabolism and secretion of many organic cationic drugs. — Sinclair, C. J., K. D. Chi, V. Subramanian, K. L. Ward, and R. M. Green. Functional expression of a high affinity mammalian hepatic choline/organic cation transporter. J. Lipid Res. 2000. 41: 1841;–1848.

Supplementary key words: choline, liver, phospholipid

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