Immunocytochemical localization of natriuretic peptide sequences in the human right auricle

Samples of the right auricle from ten patients undergoing surgery were processed for the immunocytochemical localization of atrial natriuretic peptide sequences (ANP-28 and the 26-92, 26-55 and 56-92 segments of the prohormone) using commercially available antisera and labelled with protein-A gold. Single antigen and double antigen (ANP-28 and one other) detection procedures were employed. The results show that there is no correlation between the ultrastructural appearance of specific heart granules and the molecular form of their ANP content. All specific granule types contain the full range of prohormone sequences. D granules are few and appear to be recently budded from the Golgi apparatus, whereas A and B profiles comprise the majority of specific granules and are more widely distributed in the cytoplasm. In the Golgi elements, peptide immunoreactivity is principally associated with the membrane but a proportion lies within the of vesicles and becomes concentrated within the core of developing granules. The density of ANP-immunoreactivity is higher in A profiles than in the other types. Multivesicular bodies are not intrinsically immunoreactive for ANP, nor are the numerous synaptic nerve profiles which are present in atrial muscle. In two elderly patients the basal lamina of myocytes was heavily labelled for ANP.