Light Microscopic Autoradiography and Ultrastructural Cytochemistry of Sulfated Proteoglycans in Degenerated Chondrocytes of Rat Epiphyseal Cartilage

Degenerating chondrocytes are often localized in the lower hypertrophic and calcifying zone of rat epiphyseal cartilage. The ability of these degenerating chondrocytes to synthesize and secrete sulfated proteoglycans was investigated using the light microscopic radiosulfate labeling method and the high-iron diamine-thiocarbohydrazide-silver proteinate (HID-TCH-SP) method for sulfated complex carbohydrates at the ultrastructural level. At 30 min following intraperitoneal (IP) injection of 35SO4, only intracellular autoradiographic labeling was observed, whereas both intracellular and extracellular radiosulfate labeling was seen at 1 h postinjection. A gradual increase in intracellular and extracellular labeling was seen at 3, 12 and 24h following IP injection of 35SO4. In ultrastructural cytochemical preparations, HID-TCH-SP weakly to moderately stained the chondrocyte Golgi vacuoles or immature and intermediate secretory granules but did not stain Golgi saccules. Mature secretory granules and extracellular matrix granules demonstrated strong staining. These results therefore indicate that proteoglycans are sulfated in the degenerating chondrocyte Golgi vacuoles, packaged in the secretory granules and then released into the extracellular matrix to form matrix granules.