The Use of p-Phenylenediamine in the Block to Enhance Osmium Staining for Electron Microscopy

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Abstract
Pieces of tissue 1 mm3 of rat renal medulla and cortex and rabbit myocardium were fixed in 2 or 4% glutaraldehyde, washed in buffer, postfixed in OsO4, rinsed in 70% alcohol, treated with 0.5–1% p-phenylenediamine in 70% alcohol 15–25 min, dehydrated, and embedded in Epon. Ultrathin sections were viewed in the electron microscope without further staining. Contrast was adequate except at very high magnification, when additional lead staining was required. In general, the appearances were similar to those seen after conventional lead staining. However, lipid droplets in myocardium and medullary interstitial cells were densely stained, and there was a tendency for extracellular material on the luminal surface of renal tubular epithelium and myocardial capillary endothelium also to stain densely. The main value of the method lies in the elimination of the need for section staining in both light and electron microscopy.