LIPID-COMPOSITION OF THE MEMBRANES FROM CELLS OF 2 RAT-TUMORS AND ITS RELATIONSHIP TO TUMOR THERMOSENSITIVITY

A plasma membrane-rich fraction has been separated from liver cells and cells of two solid rat tumors, D23 hepatoma and MC7 sarcoma. On the basis of marker enzyme activity the membranes separating at the 31-41% interface on the discontinuous sucrose gradient were enriched 15- to 19-fold. No significant differences in the phospholipid (PL) composition of the three membrane fractions were observed. The PL fatty acid (FA) composition showed that the percentage of unsaturated FA in all three membranes was between 43 and 48%. However, the oleic acid: PUFA ratio was much greater from tumor membranes. Membrane cholesterol was also significantly lower for cells from both tumors compared with liver cells. The DPH fluorescence polarization of the membrane fractions showed that the membranes from cells of both tumors are significantly less ordered than those of liver at all temperatures measured (4-50°C). The Mg2+ ATPase activity of the plasma membranes is inactivated by hyperthermia treatments. The enzyme from liver cells was more thermostable (LT50 = 53.86°C) than that from cells of either D23 (LT50 = 47.51°C) or MC7 (LT50 = 46.34°C) tumors.