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High Ca content of pacemaker tissues in the frog heart

Y Fukuda

    The Japanese Journal of Physiology
    |January 1, 1984
    PubMed

    Insights

    Calcium levels are significantly higher in bullfrog heart pacemaker tissues compared to other cardiac regions. This stored calcium may play a role in the heart's spontaneous pacemaker activity.

    Area of Science:

    • Cardiovascular Physiology
    • Comparative Physiology
    • Biochemistry

    Background:

    • The bullfrog heart exhibits distinct regions with specialized functions, including pacemaker tissues responsible for initiating cardiac rhythm.
    • Understanding the ionic basis of cardiac automaticity is crucial for comprehending heart function across species.

    Purpose of the Study:

    • To investigate the distribution and potential role of calcium (Ca) in different regions of the isolated perfused bullfrog heart.
    • To explore the relationship between stored calcium and spontaneous pacemaker activity in cardiac tissues.

    Main Methods:

    • Isolated perfused bullfrog heart preparation.
    • Determination of cation (specifically calcium) content in various cardiac regions, including sinus venosus, atrio-ventricular ring muscle, atria, and ventricles.
    • Assessment of calcium content under conditions of extracellular calcium deficiency.

    Main Results:

    • Calcium content was markedly elevated in pacemaker tissues (sinus venosus and atrio-ventricular ring muscle) compared to atrial and ventricular muscles.
    • This higher calcium concentration persisted even when extracellular calcium was deficient, suggesting significant intracellular or stored calcium pools in pacemaker regions.
    • Pacemaker tissues demonstrated a higher capacity for calcium storage relative to contractile tissues.

    Conclusions:

    • Pacemaker tissues of the bullfrog heart possess a significantly higher intrinsic calcium content than other cardiac regions.
    • Stored calcium in pacemaker tissues is a potential key factor contributing to their spontaneous electrical activity and automaticity.
    • These findings highlight regional differences in calcium handling within the amphibian heart and its functional implications for cardiac rhythm generation.

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