Role of Na+, K+-ATPase α1 subunit in the intracellular accumulation of cisplatin

The present study was undertaken to identify what regulates intracellular cisplatin (CDDP) accumulation and what changes in membrane fraction of CDDDP-resistant cell line. The CDDP-resistant rat hepatoma cell line, H4-II-E/CDDP, shows a significant decrease in intracellular platinum accumulation compared with parental H4-II-E cells, although there was no difference in the efflux of CDDP between these two cell lines. In this study, we examined the contribution of functional change in active transportto the CDDP resistance of H4-II-E/CDDP cells. Compared with the resistant cells, platinum accumulation in the parental cells was clearly decreased by low temperature or ATP depletion. In addition, the Na+, K+- ATPaseinhibitor ouabain and the K+ channel inhibitor tetraethylammoniumdecreased platinum accumulation in parental cells but did not change the accumulation in resistant cells. Amphotericin B, an antifungal agent, increased the intracellular platinum accumulation in resistant cells to the same level as in parent cells. Western blot analysis demonstrated that the Na+, K+- ATPaseα1 subunit was reduced in resistant cells compared with the parental cells, although there was no difference in the expression of the β1 subunit between the two cell lines. Furthermore, the Na+, K+- ATPaseα1 subunit of H4-II-E was decreased following a 24-h exposure to CDDP. These results suggest that Na+, K+- ATPase-dependent active transportof CDDP does not occur in resistant cells, and, furthermore, our findings provide the first evidence that the Na+, K+- ATPaseα1 subunit plays an important role in the transport of CDDP.