[Regulation of cell cycles of rat embryo cells in culture]

Phospholipid metabolism of 3T3 mouse fibroblasts after serum stimulation and through the G1 and S cell cycle phases : incorporation and disappearance of 32P

Phospholipid metabolism of 3T3 mouse fibroblasts has been studied after serum stimulation of arrested cells. The study of [32Pi] incorporation shows : a) in the case of PE and PC an early peak of incorporation in the G1 phase of the cell cycle, 6 hours after serum addition; b) in the case of PI an intense initial increasing of the incorporation which continues up to a S phase peak. The study of the disappearance of [32P] Phosphate from the different phospholipids points out: a) at the beginning of serum stimulation, an intense breakdown of PI, that continues through the G1 and S phases. Except at the onset, the breakdown of PI, is at any time exactly compensated for by synthesis : the two phenomena are closely linked; b) a synthesis of PE, from PC probably, at the G1 phase, 4 hours after the serum addition and the beginning of the chase experiment.

Influence of potassium and calcium ions on the phosphatidylinositol and phosphatidylcholine metabolism in rat fibroblasts after growth stimulation by calf serum

In secondary cultures of embryonic rat fibroblasts which were arrested in G1 (G0) by serum depletion and subsequently triggered into the cell cycle by readdition of growth factors isolated from fetal calf serum the influence of the potassium and calcium concentrations in the medium on phosphatidylinositol and phosphatidylcholine metabolism was investigated. The incorporation of inorganic [32P]phosphate into phosphatidylinositol is dependent on the potassium content of the culture medium. The specific activity of 32P in phosphatidylinositol is increased at K+ concentrations between 0.1 and 1 mM. Also calcium (between 0.01 and 2 mM) slightly stimulates phosphatidylinositol metabolism. Also the incorporation of myo-[3H]inositol is increased at potassium concentrations between 0.2 and 1 mM, whereas calcium is slightly inhibitory. The labelling of phosphatidylcholine with either [32P]phosphate or [3H]choline is not dependent on the potassium and calcium concentrations of the culture medium. Moreover, the phospholipid metabolism of permanently growing epithelioid and fibroblastoid cells lines, which were investigated, is considerably less dependent on the K+ and Ca2+ ions.