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Nucleoside uptake in rat liver parenchymal cells
J Mercader1, M Gomez-Angelats, B del Santo
1Departament de Bioquímica i Biologia Molecular, Universitat de Barcelona, Spain.
The Biochemical Journal
|August 1, 1996
Summary
Rat liver cells have two Na(+)-dependent nucleoside transporters. Nitrobenzylthioinosine (NBTI) stimulates one transporter, suggesting complex nucleoside uptake mechanisms in liver parenchymal cells.
Area of Science:
- Cell Biology
- Biochemistry
- Membrane Transport
Background:
- Liver parenchymal cells exhibit nucleoside transport critical for cellular metabolism.
- Previous studies identified plasma membrane nucleoside transport in liver cells.
Purpose of the Study:
- To characterize the Na(+)-dependent and Na(+)-independent nucleoside transport activities in rat liver parenchymal cells.
- To investigate the role of Nitrobenzylthioinosine (NBTI) in modulating nucleoside transport.
Main Methods:
- Uptake assays using radiolabeled uridine in isolated rat liver parenchymal cells.
- Kinetic analysis to determine K(m) and Vmax values for nucleoside transport.
- Inhibition studies using various nucleoside analogues and N-ethylmaleimide.
- Assessment of NBTI effects on nucleoside transport.
Main Results:
- Two distinct Na(+)-dependent nucleoside transport systems were identified, with different substrate specificities.
- Na(+)-dependent uridine transport showed apparent K(m) of 8-13 microM and Vmax of 246 pmol/3 min/10(5) cells.
- Nitrobenzylthioinosine (NBTI) significantly stimulated Na(+)-dependent uridine uptake, indicating a regulatory role.
- Na(+)-independent transport was insensitive to NBTI and N-ethylmaleimide.
Conclusions:
- Rat liver parenchymal cells possess at least two Na(+)-dependent nucleoside transporters with distinct properties.
- NBTI stimulates Na(+)-dependent nucleoside transport, likely by altering Vmax, not by inhibiting efflux.
- These findings elucidate the complexity of nucleoside uptake regulation in liver cells.