Rb⁺ influxes differentiate between growth arrest of cells by different agents

Summary

The effect of cell cycle on Rb⁺ (K⁺) fluxes was studied in NIH 3T3 mouse fibroblasts. Serum starvation or isoleucine deprivation resulted in cell arrest at an earlyG ₁/G ₀ phase, accompanied by a marked decrease in both ouabainsensitive and ouabain-resistant Rb⁺ influx. On the other hand, cells arrested at lateG ₁/G ₀ phase by hydroxyurea treatment have high ouabain-sensitive and ouabain-resistant Rb⁺ influx. Butyric acid treatment resulted in cell arrest at an earlyG ₁/G ₀ phase, but in contrast to serum or isoleucine starvation did not decrease Rb⁺ influxes. It is thus shown that quiescent cells may have Rb⁺ influx rates as high as that of logarithmically growing cells. The results are consistent with the hypothesis that an increased ion permeability of the cell is initiated at a critical stage inG ₁/G ₀ phase, and that butyric acid may arrest the cell beyond that stage.