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Hyperthyroidism selectively modified a transient potassium current in rabbit ventricular and atrial myocytes
Y Shimoni1, H Banno, R B Clark
1Department of Physiology, Hebrew University Medical School, Jerusalem, Israel.
The Journal of Physiology
|November 1, 1992
Summary
Hyperthyroidism significantly increases transient outward potassium currents (I(t)) in rabbit ventricular cells, altering their rate dependence. These changes, likely due to more active channels, were not observed in atrial cells.
Area of Science:
- Cardiology
- Electrophysiology
- Endocrinology
Background:
- Thyroid hormones influence cardiac function.
- Transient outward potassium currents (I(t)) play a crucial role in cardiac repolarization.
Purpose of the Study:
- To investigate the effects of hyperthyroidism on I(t) in rabbit cardiac myocytes.
- To compare changes in ventricular and atrial myocytes.
Main Methods:
- Whole-cell voltage clamp technique to record I(t) in single cardiac myocytes.
- Cell-attached patch recordings to analyze single-channel activity.
- Comparison between myocytes from normal and hyperthyroid rabbits.
Main Results:
- Hyperthyroidism markedly increased I(t) magnitude (4-5 fold) in ventricular myocytes.
- Altered rate dependence of I(t) in hyperthyroid ventricular cells, with sustained current at higher rates.
- Single-channel analysis revealed an increased number of active channels, not altered conductance, in hyperthyroid ventricular cells.
- No significant changes in I(t) magnitude or rate dependence were observed in hyperthyroid atrial myocytes.
Conclusions:
- Hyperthyroidism profoundly alters I(t) in ventricular myocytes, affecting both current magnitude and rate-dependent properties.
- The increased I(t) in hyperthyroid ventricles is attributed to an increased number of functional potassium channels.
- Atrial myocytes exhibit resistance to these hyperthyroidism-induced electrophysiological changes.