Einfluß von Serum auf die Eliminierung von Phospholipiden aus embryonalen Rattenfibroblasten in Kultur /Influence of Serum on the Release of Phospholipids from Embryonic Rat Cells in Culture

Abstract

The phospholipids of embryonic rat fibroblasts in tissue culture have been labelled with [3H] (myo) inositol, [3H] choline, [3H] glycerol and inorganic 32P , respectively. After 24 hours in serum-free medium the cells have been triggered by fetal calf serum or by a mixture of the growth-stimulating serum proteins S1 and S2, and the phospholipids were examined. 1. Up to 15 - 20 percent of total radioactivity are eliminated from the phospholipid fraction during 30 min after stimulation, when the cells have been prelabelled with [3H ]inositol; within 2 hours, however, the original value is restored. When the cells are prelabelled with 32P, the radio­ activity also decreases, but in contrast to the experiments with [3H] inositol it remains low. From this result one must conclude that part of the PI in the membranes is broken down after stimula­ tion, and that the inosit moity is reutilized for newly synthesized PI. After stimulation, a small amount of labelled PI is also found in the culture medium . 2. The elimination of radioactivity does not exclusively take place in phase. It can also be demonstrated with cells in S after removal of serum for one hour and readdition. 3. The loss of radioactivity cannot be demonstrated when the cells are triggered by dialysed fetal calf serum or by the serum factors S1 and S2. Examination of the dialysate revealed phosphatidvlinositol as compound which necessarily must be present for the elimination process after stimulation. This elimination process is also demonstrable if the biosynthesis of PI is blocked by gamma-or delta-hexachlorocyclohexane, whereas the beta derivative is completely ineffective.