Role of the Na+, K(+)-adenosine triphosphatase in the accumulation of cis-diamminedichloroplatinum(II) in human ovarian carcinoma cells.
We examined the importance of the Na+, K(+)-ATPase in cisplatin (DDP) accumulation in 2008 human ovarian carcinoma cells and describe changes in the Na+, K(+)-ATPase in DDP-resistant cells with DDP accumulation defects. Approximately 50% of DDP accumulation was inhibitable by ouabain. DDP accumulation into 2008 cells could be maximally inhibited when cells were preincubated with ouabain for 1 h prior to DDP exposure. The half-maximal inhibition was obtained with 0.13 microM ouabain. Similar inhibition of DDP accumulation was obtained when the Na+, K(+)-ATPase was blocked by ATP depletion or by incubating cells in K(+)-free medium. This same percentage of DDP accumulation was Na+ dependent and varied directly with Na+ concentration. These effects on DDP accumulation could be detected as early as 1 min after the imposition of 0-trans conditions, strongly suggesting that the inhibition was due to modulation of a drug influx step. The Na+, K(+)-ATPase in 2008/DDP cells had a similar KD for ouabain binding and 36% less Na+, K(+)-ATPase molecules/mg of protein than 2008 cells. 2008/DDP cells 2.3 +/- 0.2 (SE, n = 3) fold cross-resistant to ouabain in a continuous exposure clonogenic assay. Despite these changes in the Na+, K(+)-ATPase, the net basal Na+, K(+)-ATPase activity was the same in sensitive and DDP-resistant cells as determined by ouabain-inhibitable 86Rb+ influx. The basal Na+ levels were also similar in the sensitive and resistant cells. These data suggest that DDP accumulation is partially Na+ dependent and that, therefore, the Na+, K(+)-ATPase which maintains the Na+ gradient may play an important role in determining how much DDP enters cells. Whether there is a causal link between the changes in the Na+, K+-ATPase in DDP-resistant cells and their DDP accumulation defect is not yet known.
Andrews
P A
PA
Cancer Center, University of California, San Diego, La Jolla 92093.
Mann
S C
SC
Huynh
H H
HH
Albright
K D
KD
D002945:Cisplatin / Q000378:metabolism*; D003536:Cystadenocarcinoma / Q000378:metabolism*; D005260:Female; D006801:Humans; D010042:Ouabain / Q000494:pharmacology; D010051:Ovarian Neoplasms / Q000378:metabolism*; D012964:Sodium / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000032:analysis / Q000502:physiology*; D014407:Tumor Cells, Cultured
D010042:Ouabain; D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase; D002945:Cisplatin