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Related Experiment Videos

Thyroid hormones differentially affect sarcoplasmic reticulum function in rat atria and ventricles

A Kaasik1, A Minajeva, K Paju

  • 1Department of Pathophysiology, University of Tartu, Estonia.

Molecular and Cellular Biochemistry
|December 24, 1997
PubMed
Summary

Thyroid hormones significantly impact heart muscle function by increasing sarcoplasmic reticulum (SR) Ca(2+)-pump activity. This enhances contractility and relaxation, especially in atria, altering calcium handling in both hyperthyroidism and hypothyroidism.

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Area of Science:

  • Cardiology
  • Endocrinology
  • Molecular Biology

Background:

  • Thyroid hormones play a crucial role in regulating cardiac function.
  • Altered thyroid states, such as hypothyroidism and hyperthyroidism, can significantly affect myocardial contractility and relaxation.
  • The sarcoplasmic reticulum (SR) is a key organelle involved in calcium handling within cardiac cells.

Purpose of the Study:

  • To compare the effects of hypothyroidism and hyperthyroidism on sarcoplasmic reticulum (SR) Ca(2+)-pump activity.
  • To assess the functional role of the SR in providing activator Ca2+ under altered thyroid states.
  • To elucidate the differential impact of thyroid hormones on atrial and ventricular contractility and calcium dynamics.

Main Methods:

  • Measurement of sarcoplasmic reticulum (SR) Ca(2+)-pump activity in atrial and ventricular tissues.

Related Experiment Videos

  • Assessment of contractility (+dT/dt) and relaxation (-dT/dt) under varying thyroid states.
  • Evaluation of the recirculation fraction of activator Ca2+ (RFA) and the effect of ryanodine.
  • Analysis of the force-frequency relationship (FFR) in different cardiac preparations.

    • Main Results:

    • SR Ca(2+)-pump activity increased 10-fold in atria and 2-fold in ventricles when shifting from hypothyroid to hyperthyroid states.
    • Atrial contractility and relaxation showed greater fold increases (8-9 fold) compared to ventricular counterparts (3-4 fold).
    • The recirculation fraction of activator Ca2+ (RFA) and ryanodine inhibition were significantly higher in atria than in papillary muscles.
    • A positive FFR was observed in hypothyroid atria, while hyperthyroid atria and both hypothyroid/hyperthyroid papillary muscles exhibited a negative FFR.

    Conclusions:

    • Hypothyroid atria rely more on transsarcolemmal (SL) Ca2+ and less on SR Ca2+ for contraction compared to other preparations.
    • Thyroid hormones decrease SL Ca2+ contribution and increase SR Ca2+ contribution to contraction, with a greater effect in atria than ventricles.
    • Enhanced SR Ca(2+)-pump stimulation in atria underlies the greater impact of thyroid hormones on atrial calcium handling and function.