Ultrastructural and biochemical study of extracellular matrix vesicles in normal alveolar bone of rats

The occurrence of vesicles in the extracellular matrix of alveolar bone of normal young rats was demonstrated by both ultrastructural and enzymatic studies. Transmission electron microscopy revealed abundant vesicles in the matrix. The presence of hydroxyapatite crystals, both within the vesicles and in the matrix, was affiliated with rupture of the vesicular membrane. Calcifying nodules were scarce. High levels of both specific and total activities of alkalineand pyrophosphatases were found in the fraction of isolated vesicles. This fraction also showed activities of different ATPases and acid phosphatase.