Effect of Rb+ Substituted for K+ on HeLa Cells: Cellular Content and Membrane Transport of Monovalent Cations, and Cell Growth

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The usefulness of Rb⁺ was investigated as an analog of K⁺ in membrane transport and in supporting the growth of HeLa cells. On replacement of extracellular K⁺ by Rb⁺, intracellular Rb⁺ content increased linearly at 15 min. K⁺ content declined in contrast with Rb⁺, but Na⁺ content was unaffected. In Rb⁺-preloaded cells, Rb⁺ and K⁺ were exchanged after replacement of extracellular Rb⁺ with K. A kinetic analysis of intracellular Rb⁺ content showed that most K⁺ was exchangeable with Rb⁺, but a small part of K⁺ was not. Both Rb⁺ and K⁺ influxes were equally inhibited by ouabain or furosemide. Rb⁺ efflux was repressed by furosemide, whereas K⁺ efflux wasnot influenced. When 90 % of K⁺ was replaced by Rb⁺ in serum-free chemically defined medium, cell growth and protein synthesis were inhibited. After total replacement of extracellular K⁺ by Rb⁺, cell growth ceased and cellular protein content decreased, while a small part of intracellular K⁺ remained unexchanged. HeLa cells seemed to accumulate Rb⁺ in preference to K⁺.