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Thyroid status and diabetes modulate regional differences in potassium currents in rat ventricle
Y Shimoni1, D Severson, W Giles
1Department of Medical Physiology, University of Calgary, Alberta, Canada.
The Journal of Physiology
|November 1, 1995
Summary
Altered hormonal status selectively impacts potassium currents (I(t)) in rat heart cells, affecting action potential duration and reducing regional differences. This research highlights how thyroid and diabetic conditions modify cardiac electrophysiology.
Area of Science:
- Cardiovascular Physiology
- Cardiac Electrophysiology
- Ion Channel Function
Background:
- Epicardial and endocardial myocytes exhibit distinct electrophysiological properties.
- Differences in potassium currents contribute to regional variations in action potential duration and refractoriness.
Purpose of the Study:
- To investigate the rate dependence and recovery kinetics of outward potassium currents (I(t) and Iss) in rat ventricular myocytes.
- To determine the effects of altered hormonal status (thyroid and diabetic) on these currents and their regional differences.
Main Methods:
- Whole-cell, suction microelectrode technique used to measure I(t) and Iss in isolated epicardial and endocardial myocytes.
- Comparison of control animals with groups subjected to hypothyroid, hyperthyroid, and streptozotocin-induced diabetic conditions.
Main Results:
- Transient outward potassium current (I(t)) was smaller in endocardial cells due to slower recovery kinetics, prolonging action potentials.
- Steady-state outward potassium current (Iss) showed similar magnitude and rate dependence in both regions.
- Hypothyroidism reduced I(t) more in epicardial cells, while diabetes caused greater I(t) attenuation in epicardial cells.
- Hyperthyroidism accelerated I(t) recovery in endocardial cells.
Conclusions:
- Altered hormonal status differentially affects I(t) amplitude and kinetics in epicardial and endocardial cells.
- These hormonal influences can diminish the electrophysiological gradients between epicardial and endocardial regions.
- Changes in I(t) kinetics under altered hormonal conditions impact action potential duration and refractoriness, with potential implications for cardiac arrhythmias.