To visualize proteoglycans histochemically, tissue blocks from rat tracheal cartilage were fixed with a paraformaldehyde solution containing cetylpyridinium chloride, embedded in LR-White, stained with a postembedding method of ruthenium red-tungstate (RR-PTA) sequence and examined in a transmission electron microscope.
In the intercellular matrices of the cartilage tissues, a number of RR-PTA reactive, electron dense deposits were scattered in irregularly shaped clumps of different sizes. In the matrices adjacent to chondrocytes, RR-PTA reactive structures were regularly arranged in filamentous shapes. If digested with testicular hyaluronidase, both the RRPTA reactive structures in the extracellular matrices were either markedly decreased or abolished. Thus, these structures could be regarded as molecules of chondroitin sulfate (A and/or C) proteoglycans. In view of the dimensions of the RR-PTA reactive structures adjacent to chondrocytes, they could be taken to represent large molecules of proteoglycan aggregates in the cartilage tissues.