Ultrastructural and cytochemical aspects of the initial phases of an experimental cutaneous calcinosis (calcergy) in the rat.

In rats a subcutaneous injection of KMnO4 leads to the calcification of the connective tissue. During mineral deposition, both intra- and extracellular changes are observed in the connective tissue. The intracellular phase is characterized by the formation of intramitochondrial granules and cytoplasmic vesicles, both in fibroblastic and extrinsic cells. In the extracellular phase, numerous heterogeneous matrix vesicles appear in the extracellular matrix. At the same time, globular particles which are resistant to microincineration, are observed between the collagen fibrils. The mineralization of the extracellular matrix takes place in two stages. The first stage comprises the appearance of needle-like structures and round aggregates. The needle-like structures are observed occasionally in the matrix vesicles and often in the extracellular matrix where they appear isolated or diverging from a central point. The round aggregates, composed of dense particles, are seen in the ground substance between the collagen fibrils. The second stage is characterized by a progressive mineralization of the collagen fibrils and the elastic fibers, without formation of extended calcified plaques.