CHROMOGRANIN A: IMMUNOCYTOCHEMICAL LOCALIZATION IN SECRETORY GRANULES OF FROG ATRIAL CARDIOMYOCYTES
M. I. Krylova
Institute of Cytology RAS, St. Petersburg;
e-mail: heartdev@mail.cytspb.rssi.ru
Chromogranin A (CgA) is a member of the granin family of acidic proteins that present in the secretory granules
(SGs) of many endocrine, neuroendocrine and neuronal cells. Atrial natriuretic peptide (ANP)-storing SGs in atrial
cardiomyocytes of rat heart also contain CgA. Cardiosuppressive effect of CgA-derived peptides (vasostatins) on
in vitro isolated and perfused working frog and rat hearts has been shown under both basal conditions and
beta-adrenergic stimulation. More recently it has been revealed that rat heart produces and processes CgA-derived
vasostatin-containing peptides. Until now nothing has been known about the presence of CgA in an amphibian heart.
We have investigated the subcellular localization of CgA in atrial myocytes of adult frog Rana temporaria heart
using ultraimmunocytochemical method. Immunocytochemical staining of the frog atrial tissue for CgA and ANP has shown
that out of three morphologically different types (A, B and D) of specific cytoplasmic granules (SCGs) present in
myocytes only two (A and B) - large (120-200 nm in diameter) granules with more and with less electron dense core -
exhibit immunoreactivity (IR) to these two antigens. The third type (D) of granules (80-100 nm in diameter) are small
membrane bound granules characterized by highly electron dense core surrounded with a thin halo. These granules
revealed negative reaction on immunostaining for both CgA and ANP. The presence of CgA- and ANP-IR in the same SCGs
in frog atrial myocytes is consistent with the endocrine nature of these granules. Taking into account our and
literature data we propose that CgA present in frog atrial cardiomyocite SCGs might be a precursor of vasostatin-
containing peptides, as it takes place in rat heart. It is possible that these CgA-derived peptides together with ANP
exert their regulatory function through the autocrine and/or paracrine mechanisms and play important cardioprotective
role in frog heart under stress condition.
Key words: chromogranin A, atrial cardiomyocytes, specific secretory granules, ultrastructural
immunocytochemistry, frog Rana temporaria
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