Transition metal ions induce cell growth in NRK cells synchronized in G1 by picolinic acid

The G₁ arrest induced in NRK cells by picolinic acid could be prevented by addition of Fe³⁺, Zn²⁺ or Co²⁺ to the tissue culture media. Ca²⁺, Mg²⁺, Mn²⁺, Sr²⁺ or Ba²⁺ were ineffective. Complete and synchronous reversal of the G₁ block, however, was achieved by Fe³⁺ at lower concentration from that of Zn²⁺. Co²⁺ reversed the block but cells divided asynchronously. Thymidine incorporation, mitotic index and relative DNA content per cell, verified that G₁ arrested cells proceeded through the cell cycle after addition of Fe³⁺ or Zn²⁺. These observations afford a valuable model system for elucidating the biochemical events that occur between addition of a defined proliferative signal and stimulation of DNA synthesis in G₁ arrested cells.