Hypoxanthine transport and transient expression of possible regulatory proteins in COS-1 cells

We have demonstrated that monkey kidney (COS-1) cells have a single type of nucleobase transport process. The system is sodium-independent, and transport of hypoxanthine was insensitive to inhibition by nitrobenzylthioinosine (NBMPR), but was inhibited by nucleosides. These properties are consistent with hypoxanthine transport occurring via the NBMPR-insensitive nucleoside carrier (ei). Transfecting COS-1 cells with opossum kidney cDNA fractions resulted in similar to 70% inhibition of hypoxanthine influx suggesting the possible presence of genes within the library that act as apparent inhibitors of hypoxanthine transport. Further studies are required to clarify the nature of this inhibition, but the COS-1 expression system appears to be a useful tool for the possible identification of important regulatory proteins.