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Electron microscopists have described in vascular endothelial cells filaments which resemble myofibrils. These fibrils cannot be demonstrated with conventional staining techniques. On the basis of previous investigations of relations between dye structure and affinity for muscle fibres, a staining method for demonstration of myoendothelial cells by direct, polarization and fluorescence microscopy has been developed. Carnoy-fixed paraffin sections were treated consecutively with Kernechtrot, tannic and phosphomolybdic acid and counterstained with Levanol fast cyanine 5RN. This procedure stained myoendothelial cells and muscle fibres deep blue, connective tissues yellow and nuclei pink. For polarization and fluorescence-microscopic studies thiazine red R was substituted for Levanol fast cyanine 5RN and Kernechtrot was replaced by Mayer's acid haemalum. The light-microscopic characteristics of fibrils in endothelial cells and in smooth muscle cells were identical.Correlation of light-microscopic observations with electron-microscopic data supported the conclusion that the staining procedure indeed demonstrates myofilaments in endothelial cells. Formation of multiple layers of myoendothelial cells was observed in areas of thickening of the intima, while the cells in the deeper layers became indistinguishable from smooth muscle cells. These findings support earlier concepts of the transformation of endothelial cells into intimal muscle cells.

To facilitate studies of early myocardial lesions a method was developed for simultaneous demonstration of saccharides and muscle proteins. Deparaffinized sections were treated consecutively with the PAS reaction, tannic acid, phosphomolybdic acid and Levanol fast cyanine 5RN. A and Z bands in normal muscle were stained blue. I bands were coloured yellow. Under various pathological conditions A and Z bands lost their affinity for Levanol fast cyanine 5RN, with and without appearance of PAS-positive material in the Z bands.Comparison of staining patterns with chemical, electron microscopic and X-ray diffraction data indicated that Levanol fast cyanine 5RN is bound by myosin and tropomyosin B. This affinity is lost when the protein structure is altered. The origin of the PAS-positive material appearing in the Z bands could not yet be determined.