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Thyroid status and potassium currents in rat ventricular myocytes
1Department of Medical Physiology, University of Calgary, Alberta, Canada.
The American Journal of Physiology
|February 1, 1995
Summary
Hypothyroidism significantly reduces outward potassium currents (Ito) in rat ventricular myocytes, altering their electrical activity. Thyroid hormone replacement therapy reversed these effects, highlighting thyroid status
Area of Science:
- Cardiology
- Endocrinology
- Molecular Physiology
Background:
- Thyroid hormones play a crucial role in regulating cardiac function.
- Alterations in thyroid status can lead to significant cardiovascular changes.
- Potassium currents are critical determinants of cardiac action potential and rhythm.
Purpose of the Study:
- To investigate the impact of hypothyroidism and hyperthyroidism on cardiac potassium currents.
- To determine the effects of altered thyroid status on the rate-dependent properties of these currents.
- To assess the reversibility of these changes with thyroid hormone replacement.
Main Methods:
- Isolated rat ventricular myocytes from euthyroid, hypothyroid, and hyperthyroid rats.
- Whole-cell, suction electrode voltage-clamp technique.
- Measurement of transient (Ito) and steady-state (Iss) outward potassium currents.
Main Results:
- Hypothyroidism reduced Ito amplitude and slowed its recovery kinetics, enhancing rate dependence.
- Iss amplitude was unchanged in hypothyroidism but increased in hyperthyroidism.
- Thyroid hormone (T3) replacement reversed hypothyroidism-induced current changes.
- Hyperthyroidism did not significantly alter Ito but increased Iss amplitude.
Conclusions:
- Thyroid status profoundly modulates cardiac potassium currents.
- Hypothyroidism affects Ito properties, impacting action potential rate dependence.
- These findings underscore the link between thyroid hormones and cardiac electrophysiology.