Electron Microscopic Study of the Intercellular Activity of Alkaline Phosphatase in Rat Epiphyseal Cartilage

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Abstract
Epiphyseal cartilage from rat tibia was treated by the ruthenium red method and lead citrate method to demonstrate the presence and distribution of alkaline phosphatase, examined by electron microscope. Enzyme activity first appeared as electron dense precipitates at the plasma membrane of chondrocytes in the proliferative zone. No precipitates were found in the intercellular matrix. In the upper part of the hypertrophic zone, electron dense precipitates were seen at the plasma membrane of chondrocytes and in association with small spherical or ovoid structures with a diameter of 800–1,200 Å which were present around chondrocytes and in the intercellular matrix. These structures were not enveloped by unit membranes. Moreover, reaction products were adherent to the outersurfaces of the investing membrane of matrix vesicles within the longitudinal septum. In the lower hypertrophic zone, reaction products were found at the plasma membrane of chondrocytes and in association with spherical or ovoid structures with a diameter of 1,000–2,000 Å which were observed around chondrocytes. In areas of advanced calcification, the reaction products around chondrocytes were in smaller quantities, but they were seen in association with variously shaped bodies with a diameter of 2,000–6,000 Å which were found within the longitudinal septum. Some of these bodies contained needle-like crystals. The possible role of the intercellular activity of alkaline phosphatase was discussed.

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