Morphological and behavioral characteristics of two rat tumor cell lines with different metastatic capacities.

The morphological characteristics of two rat tumor cell lines were studied by means of scanning electron microscopy. While the ASML-cells (Ascites, Solid, Metastases, Lung) when spread via the lymphatic vessels form metastases in the lung, the AS-cells (Ascites, Solid) do not form secondary tumors. The ASML-cells do not attach on glass or plastic but grow in suspension; AS-cells, can be cultivated as monolayers. The ASML-cells form loosely packed clusters when they are shaken in a gyratory shaker, AS-cells produce well organized aggregates in which the intercellular contacts are very intensive. When a mixture of cells from both lines is aggregated the two types sort out and the line-specific aggregate or cluster is formed without interaction between the two types. ASML-cells remain spherical when confronted with pieces of the aortic wall and there are no signs of reaction with the underlying endothelial cells. The endothelium is drastically altered when AS-cells are seeded on top of the aortic wall: the tumor cells flatten, penetrate the endothelial layer and induce the endothelial cells to retract. These phenomena can also be seen in confrontations with the mesothelium of the diaphragm. As also cells from aggregates or clusters behave as the single cells we conclude that the newly formed heterotypic contacts are favored over homotypic ones. In addition they have proved to be more intensive.