An electron microscopic and spectroscopic study of murine epiphyseal cartilage: Analysis of fine structure and matrix vesicles preserved by slam freezing and freeze substitution

Newborn mice epiphyseal growth plates were preserved by slam freezing/freeze substitution and examined by conventional electron microscopy, stereopsis, high voltage electron microscopy, and electron spectroscopic imaging (ESI). To illustrate the improved ultrastructure of this cryogenic procedure, conventional, aqueously fixed growth plates were included showing collapsed hypertrophic chondrocytes surrounded by a depleted and condensed extracellular matrix. In contrast, the cryogenically prepared epiphyses contain chondrocytes and extracellular matrix vesicles both in direct contact with proteoglycan filaments retained in an expanded state. ESI is an electron microscopic technique which enables the direct localization of atomic elements superimposed over fine structural details. This technique was used to examine the colocalization of calcium and phosphorus within matrix vesicles and within their associated extracellular environments. Matrix vesicles appeared in three distinct diameter ranges. The integrity of the matrix vesicles was examined at various stages of mineralization and also within the mineralized zone of provisional calcification.