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.