Stimulating Effect of an Artificial Electron Mediator, Phenazine Methosulfate, on Rb+ Transport in HeLa Cells

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Abstract
To obtain evidence of the action of the intracellular redox system as a regulating factor of membrane K+ transport in HeLa [human cervical carcinoma] cells, an artificial electron mediator, phenazine methosulfate (PMS) was used. An addition of PMS to the incubation medium increased the intracellular accumulation of Rb+ as an analog of K+. This increase, which was ouabain-sensitive, was shown to be due to the stimulation of active Rb+ transport. The rate of ouabain-sensitive Rb+ uptake was a linear function of the cellular bulk ATP level. When cells were treated with 20 .mu.M PMS, the linear curve showed a parallel shift upward. The range of the shift, the PMS-stimulated part of the Rb+ uptake, was independent of the ATP level. The intracellular level of Rb+ plus K+, which was equal to the K+ level in cells incubated in normal medium, was elevated slightly, but Na+ level remained unchanged. These results indicated that the stimulation of Rb+ uptake had no effect on changes in the intracellular levels of monovalent cations. The maximal rate of ouabain-sensitive Rb+ uptake, Jmax; was increased, but the apparent Km in relation to extracellular Rb+ was unaffected. The specific binding of [3H]ouabain was not enhanced. The total number of Rb+ binding sites and the affinity of Rb+ to those sites would not be affected significantly. Apparently the stimulating action of PMS is due either the acceleration of Rb+ pumping at each Na+, K+-pump or to activation of the resting pumps.