Pleomorphic surface features of mammalian endocardium: fine structure of canine bicuspid valves

SEM and TEM have demonstrated normal canine endocardium to consist of a somewhat irregularly undulating, continuous sheet of cells characterized by plasmalemmal micro-appendages, rounded and raised nuclear bulges and variably discernible, overlapping cell margins. The endocardium covering the atrioventricular valves presented the most pleomorphic surface features in that our observations of both the atrial and ventricular aspects of the valvular leaflets revealed obvious differences in cell density, micro-appendage population, nuclear prominence and glycocalyx. Cells from the ventricular surface of these valves possessed few, if any, micro-appendages and more flattened surface contours; whereas those cells over the atrial surface demonstrated numerous bleb-like to microvillous-like processes extending from distinctly rounded and raised surface contours. Valvular specimens exposed to such catonic dyes as ruthenium red, alcian blue and cetylpyridinium chloride, with the latter two accompanied by lanthanum nitrate en bloc staining, revealed an obvious surface reactivity differential between the two sides that implies a compositional difference in the glycocalyx.