An ultrastructural study of alkaline phosphatase in a transplantable rat osteogenic sarcoma

Alkaline phosphatase (AP) has been demonstrated by combined electron microscopy and histochemistry in a transplantable rat osteogenic sarcoma, using a modified Gomori technique (Salomon, 1974). During the early stages of growth of subcutaneously implanted tumors, AP was detected in intracellular membrane systems resembling Golgi and on membranes of cells and matrix vesicles. During growth of the tumor, there was extensive development of intercellular collagen, and AP was demonstrated in bodies associated with collagen. In some cases the AP-containing bodies resembled matrix vesicles, but there was considerable size heterogeneity of the AP-containing bodies, suggesting that there may be heterogeneity of matrix vesicles. The amount of detectable AP seemed to increase in all areas of the tumor which were viable, during tumor growth, but no AP could be detected in cell debris of necrotic areas of the tumor (area C) nor associated with collagen in that area. Area D, particularly during later stages of tumor growth, showed the greatest development of calcium deposits, with calcium spicules apparently associated with AP-containing bodies on both cell membranes and collagen. AP-containing bodies also appeared in large numbers in venules during later stages of tumor growth, associated with an amorphous material. This may account for the increase in serum AP activity which occurs during later stages of growth of transplanted tumors. The sites of AP activity in this osteogenic sarcoma were similar to those described in normal tissue, but generally seemed to be more abundant.