VI. Calcium- und Kaliumionen als Cofaktoren

Abstract

Embryonic rat cells are stopped in G1-phase when they are incubated in serum-free medium. They can be triggered to proceed through their cell cycle by the addition of two proteins which have been isolated from fetal calf serum. The influence of calcium and potassium ions on the stimulation process has been exam ined: 1. Ca2+ and K+ ions simultaneously must be present in the culture medium in concentrations of at least 5x10-4 ᴍ and 1x10-3 ᴍ, resp. 2. The intracellular concentrations of both ions are increased by the serum factors. 3. The intracellular concentrations of K+ strongly are dependent on the extracellular Ca2+-concentrations; they increase threefold between 5x10-5 and 1x10-3 ᴍ of Ca2+. On the other hand, the intracellular calcium concentrations are not significantly influenced by the potassium content of the culture medium.