Hepatocytes isolated from fed rats were used to investigate glutamine transport. Glutamine transport appears as a composite process involving at least two saturable components. The Na+-dependent component probably represents the entry through the N system. The Na+-independent component was also inhibited by histidine and exhibited trans-stimulation, suggestive of a facilitated diffusion process. Kinetic parameters for both systems suggest that facilitated diffusion only plays a minor role in glutamine influx. In contrast, the Km for glutamine efflux was consistent with a physiological role of the facilitated-diffusion component in glutamine release. In Na+ medium, relatively constant distribution ratios (about 8) between intra- and extra-cellular concentrations were observed, with external glutamine ranging from 0.5 to 5 mM. The present observations suggest that glutamine influx might largely be mediated by the N system, whereas facilitated diffusion allows hepatocytes to release glutamine when intracellular concentrations are elevated. The physiological consequences of this bidirectional transfer of glutamine across the liver cell membrane is discussed.
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Research Article| November 15 1983
Bidirectional transport of glutamine across the cell membrane in rat liver
Biochem J (1983) 216 (2): 401–408.
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P Fafournoux, C Demigné, C Rémésy, A Le Cam; Bidirectional transport of glutamine across the cell membrane in rat liver. Biochem J 15 November 1983; 216 (2): 401–408. doi: https://doi.org/10.1042/bj2160401
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