Morphometry of cytoplasmic components of mammalian articular chondrocytes and corneal keratocytes: species and zonal variations of mitochondria in relation to nutrition.

A morphometric analysis was made of nuclei and cytoplasmic structures in electron micrographs of chondrocytes in the non-calcified layer of articular cartilage of the femoral condyles in adult mouse and dog and of the human incus. Mitochondrial volume density (% cytoplasm) was lower in dog than in mouse cells or cells of the incus. It was also lower in the cells of deep zone cartilage than in superficial cells. Analysis of keratocytes of the corneal stroma in mouse and sheep gave similar findings to that in cartilage. Mitochondrial volume density was higher in mouse than in sheep keratocytes and, in sheep, higher in subepithelial (anterior) cells than in cells of the intermediate and subendothelial strata. Values in human stromal cells were similar to those in the sheep. Endoplasmic reticulum volume density was higher in mouse than in sheep keratocytes. Lipid and filaments were more abundant in dog than in mouse chondrocytes but keratocytes contained little or none. Mitochondrial volume densities correlate with diffusion distances (tissue thickness) from the sources of nutrition, for example, for oxygen, in the two tissues. The relationship to certain aspects of chondroitin sulphate and keratansulphate synthesis and topographical distribution in cartilage and cornea is discussed.