Some cell surface membrane properties of
tumors may depend upon the host tissue site. Therefore, local
tumors and lung
metastases were excised from athymic (nude) mice injected subcutaneously with LM fibroblasts. The excised local
tumors and lung
metastases were cultured in chemically-defined, serum-free medium to characterize their plasma membrane properties without complicating factors such as site of growth, presence of host inflammatory cells, and variation in nutrition. Plasma membranes were isolated from the cultured local
tumor cells and cultured metastatic cells. The specific activities of (N+,K+)-
ATPase and
5'-nucleotidase were elevated and decreased, respectively, in plasma membranes from metastatic cells as compared to local
tumor cells, a finding consistent with data from directly excised local
tumors and lung
metastases. Plasma membranes of metastatic cells had a lower ratio of
sterol/
phospholipid, higher ratio of
phosphatidylcholine/
phosphatidylethanolamine, and no differences in
phospholipid unsaturated/
saturated fatty acid ratio compared to plasma membranes from the locally-derived
tumor cells. Plasma membranes of metastatic cells were more fluid (lower limiting anisotropy) than those of local
tumor cells as indicated by multifrequency phase and modulation fluorometry and the fluorescence probe molecule,
1,6-diphenyl-1,3,5-hexatriene. Thus, the higher fluidity of metastatic as compared to local
tumor plasma membranes was not due to differences in site of growth, host cell contamination, and/or nutrition.