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Updated: Sep 14, 2025

Isolation of Atrial Myocytes from Adult Mice
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Isolation of Atrial Myocytes from Adult Mice

Published on: July 25, 2019

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Atrial granules as acidic calcium stores in cardiomyocytes

Emily Akerman1, Daniel Aston1, Eva A Rog-Zielinska2

  • 1Department of Pharmacology, University of Oxford, OX1 3QT Oxford, UK.

European Heart Journal Open
|July 24, 2025
PubMed

Insights

Atrial myocytes contain unique acidic granules (AGs) that store atrial natriuretic peptide (ANP). Their positioning shifts in atrial fibrillation, potentially impacting calcium signaling in heart cells.

Area of Science:

  • Cardiology
  • Cell Biology
  • Organelle Biology

Background:

  • Acidic calcium stores are crucial for cardiomyocyte function.
  • Atrial myocytes possess atrial granules (AGs), acidic, calcium-rich organelles absent in ventricular myocytes.
  • The precise number, location, and functional relevance of AGs remain largely uncharacterized.

Purpose of the Study:

  • To investigate the distribution and characteristics of acidic organelles, specifically AGs, in atrial and ventricular cardiomyocytes.
  • To explore the spatial relationship of AGs with other cellular structures, particularly in the context of atrial fibrillation (AF).

Main Methods:

  • Acidic organelle labeling in guinea pig cardiomyocytes.
  • Live cell fluorescent studies using 4-phenyl-3-butenoic acid (PBA) to inhibit AGs.
  • Immunofluorescent labeling for ANP and lysosomal markers.
  • Electron microscopy and quantitative analysis of goat atrial tissue from AF and control groups.

Main Results:

  • Acidic puncta were observed throughout cardiomyocyte cytosol, with higher concentration at nuclear poles in atrial myocytes.
  • PBA treatment specifically reduced acidic staining in atrial cells, confirming AG involvement.
  • AGs showed minimal co-localization with lysosomal markers.
  • In AF, AGs were positioned farther from sarcoplasmic reticulum and closer to mitochondria compared to sinus rhythm.

Conclusions:

  • Atrial myocytes exhibit distinct acidic organelle populations, characterized by AGs concentrated near the nucleus.
  • AG positioning is altered in atrial fibrillation, suggesting a potential role in altered cellular communication.
  • The strategic positioning of AGs may be significant for intercellular signaling and calcium handling within cardiomyocytes.

Keywords:
Atrial fibrillationAtrial granulesCardiomyocytesElectron microscopyPAM

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