The chemical nature of human atrial specific granules

The nature of human auricular specific granules was assessed by a variety of cytochemical and histochemical methods. The specific granules were found to be argentaphobic when ultrathin sections of Araldite-embedded auricular appendages were stained according to the periodic acid-thiocarbohydrazide-silver proteinate technique of Thiery. The entire core of these granules was moderately positive after ultrathin sections of glutaraldehyde-fixed, glycol methacrylate (GMA)-embedded auricles were stained with phosphotungstic acid (PTA) at a low pH. A similar reaction was shown by the cell coat, residual bodies (C-granules), lysosomes, Z-discs as well as by a very small portion of the Golgi complex. Analogous results were obtained in semithin sections of GMA-embedded auricles stained by the periodic acid-Schiff (PAS) technique. Incubation of ultrathin sections (fixed in glutaraldehyde and embedded in GMA) with proteolytic enzymes (pronase, pepsin, trypsin, or alpha-chymotrypsin) elicited selective digestion of atrial specific granules and Z-bands and, to a much lesser degree, of the cell coat. It is concluded that human auricular specific granules, as in rat atrial cardiocytes, are composed mostly of proteins. In addition, these granules may contain complex carbohydrates.