An immunocytochemical study on co-localization of cathepsin B and atrial natriuretic peptides in secretory granules of atrial myoendocrine cells of rat heart.
To examine localization of cathepsin B, a representative lysosomal cysteine protease, in atrial myoendocrine cells of the rat heart, immunohistochemistry at the light and electron microscopic level was applied to the atrial tissue, using a monospecific antibody for rat liver cathepsin B. In serial semi-thin sections, immunoreactivity for cathepsin B and atrial natriuretic peptides (ANP) was detected in the para-nuclear region of atrial myoendocrine cells. Several large granules and many fine granules in the region of the cells were positively stained by the cathepsin B antibody. Gold particles indicating cathepsin B antigenicity labeled secretory granules in the cells, which were also labeled by those indicating ANP, using thin sections of the Lowicryl K4M-embedded material. Moreover, some granules labeled densely by immunogold particles for cathepsin B seemed to be lysosomes. By double immunostaining using thin sections of the Epon-embedded material, gold particles indicating cathepsin B and ANP antigenicities were co-localized in secretory granules of the cells. By enzyme assay, activity of cathepsin B was three times higher in atrial tissue than ventricular tissue. The results suggest that co-localization of cathepsin B and ANP in secretory granules is compatible with the possibility that cathepsin B participates in the maturation process of ANP.
Watanabe
T
T
Department of Anatomy, University of Tsukuba, Ibaraki-Ken, Japan.
Watanabe
M
M
Ishii
Y
Y
Matsuba
H
H
Kimura
S
S
Fujita
T
T
Kominami
E
E
Katunuma
N
N
Uchiyama
Y
Y
D000818:Animals; D009320:Atrial Natriuretic Factor / Q000032:analysis*; D015153:Blotting, Western; D002401:Cathepsin B / Q000032:analysis*; D003594:Cytoplasmic Granules / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D006325:Heart Atria / Q000032:analysis / Q000648:ultrastructure; D006352:Heart Ventricles / Q000032:analysis / Q000648:ultrastructure; D007150:Immunohistochemistry; D008297:Male; D008854:Microscopy, Electron; D009206:Myocardium / Q000648:ultrastructure*; D051381:Rats; D011919:Rats, Inbred Strains
D009320:Atrial Natriuretic Factor; D002401:Cathepsin B