ZONE-SPECIFIC CELL BIOSYNTHETIC ACTIVITY IN MATURE BOVINE ARTICULAR-CARTILAGE - A NEW METHOD USING CONFOCAL MICROSCOPIC STEREOLOGY AND QUANTITATIVE AUTORADIOGRAPHY

A new methodology was developed to measure spatial variations in chond rocyte/matrix structural parameters and chondrocyte biosynthetic activ ity in articular cartilage. This technique is based on the use of a la ser scanning confocal microscope that can ''optically'' section chemic ally fixed, unembedded tissue. The confocal images are used for morpho metric measurement of stereologic parameters such as cell density (cel ls/mm(3)), cell volume fraction (%), surface density (1/cm), mean cell volume (mu m(3)), and mean cell surface area (mu m(2)). Adjacent piec es of tissue are simultaneously processed for conventional liquid emul sion autoradiography, and a semiautomated grain counting program is us ed to measure the silver grain density at regions corresponding to the same sites used for structural measurements. An estimate of chondrocy te biosynthetic activity in terms of grains per cell is obtained by di viding the value for grain density by that for cell density. In this p aper, the newly developed methodology was applied to characterize the zone-specific behavior of adult articular cartilage in the free-swelli ng state. Cylinders of young adult bovine articular cartilage were lab elled with either [H-3]proline or [S-35]sulfate, and chondrocyte biosy nthesis and structural parameters were measured from the articular sur face to the tidemark. The results showed that chondrocytes of the radi al zone occupied twice the volume and surface area of the chondrocytes of the superficial zone but were 10 times more synthetically active. This efficient and unbiased technique may prove useful in studying the correlation between mechanically induced changes in cell form and bio synthetic activity within inhomogeneous tissue as well as metabolic ch anges in cartilage due to ageing and disease.