Ultrastructure and histochemistry of the medullary interstitial matrix of rat kidney

Medullary tissue of the normal rat kidney was perfused with 3 percent glutaraldehyde (GA), incubated in 0.5 percent cetyl pyridinium chloride and postfixed in 1 percent OsO4. In comparison with the ordinary fixation with GA and OSO4, the medullary interstitium represented abundant matrical substance that is rich in acid mucopolysaccharides (AMPS) and morphologically represents a diffuse reticular structure consisting of 30 to 150 a thick microfibrils and granular structures of 300 to 500 A in diameter. When chondroitinase was applied before OsO4 treatment, the dense granes disappeared and the microfibrils were replaced by loosely textured 30 A thick microfilaments. After hyaluronidase treatment the microfibrils disappeared and most granules changed into a ring-shaped structure with an electronlucent central portion. These results suggest that the reticular structure consists of microfilaments of hyaluronates and amorphous masking substance of chondroitin sulfates. In the dense granule, hyaluronates become concentrated in the central portion and chondroitin sulfate in the peripheral zone. When perfused with a CPC-containing GA, the medullary interstitium was diffusely filled with a large amount of fine granular substances suggesting the presence of water soluble free AMPS filling the reticular space.