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Updated: Aug 8, 2026
Isolation of Human Atrial Myocytes for Simultaneous Measurements of Ca2+ Transients and Membrane Currents
Published on: July 3, 2013
Thyroxine effects on temperature dependence of ionic currents in single rabbit cardiac myocytes
1Department of Medical Physiology, University of Calgary Health Sciences Centre, Alberta, Canada.
Insights
Thyroid hormone levels significantly alter cardiac cell function. Hyperthyroidism reduces the temperature sensitivity of the transient outward current (I(t)) in rabbit ventricular myocytes, impacting ionic channel regulation.
Area of Science:
- Cardiology
- Electrophysiology
- Endocrinology
Background:
- Thyroid hormones play a crucial role in regulating cardiac function.
- Ionic currents in cardiac myocytes are essential for electrical activity and are influenced by various physiological conditions.
Purpose of the Study:
- To investigate the effect of thyroid hormone levels (euthyroid, hyperthyroid, hypothyroid) on the temperature dependence of ionic currents in rabbit cardiac myocytes.
- To determine if the transient outward current (I(t)) and other major currents are differentially affected by thyroid status.
Main Methods:
- Macroscopic whole-cell currents were recorded from single rabbit cardiac myocytes using the suction electrode voltage-clamp technique.
- Experiments were conducted under euthyroid, hyperthyroid, and hypothyroid conditions.
- The temperature dependence (Q10 values) of ionic currents was analyzed between 22 and 32 degrees C.
Main Results:
- In ventricular myocytes, hyperthyroidism significantly reduced the temperature dependence of the transient outward current (I(t)), with Q10 values decreasing from 6.14 to 2.14.
- L-type calcium currents and steady-state currents (reflecting inwardly rectifying potassium current) in ventricular myocytes showed minimal changes in amplitude or temperature dependence under hyperthyroid conditions.
- Atrial cells did not exhibit changes in the temperature dependence of I(t) under hyperthyroid or hypothyroid conditions, and ventricular cells also showed no change under hypothyroid conditions.
Conclusions:
- The regulation of the transient outward current (I(t)) in ventricular myocytes is uniquely sensitive to temperature and thyroid hormone levels.
- These findings highlight a specific vulnerability of ventricular I(t) to thyroid dysfunction and suggest unique mechanisms for its long-term regulation.
- The differential effects on various ionic currents underscore the complex interplay between thyroid hormones and cardiac electrophysiology.
Abstract:
Macroscopic whole cell currents were measured from single rabbit cardiac myocytes, using the suction electrode voltage-clamp technique, under euthyroid, hyperthyroid, and hypothyroid conditions. In ventricular myocytes, the temperature dependence of the transient outward current (I(t)) was greatly reduced in hyperthyroid conditions, with Q10 values (between 22 and 32 degrees C) reduced from normal values of 6.14 +/- 0.93 (SE, n = 8) to 2.14 +/- 0.14 (n = 6). In contrast, two of the other major currents in these cells were relatively unaffected. Under hyperthyroid conditions, there was very little change in the amplitudes or temperature dependence of L-type calcium currents and of steady-state currents, which reflect mainly the inwardly rectifying potassium current. In atrial cells no changes in the temperature dependence of I(t) were observed, with virtually identical Q10 values (close to 4) in eu- and hyperthyroid conditions. Under hypothyroid conditions, there was no change in the temperature dependence of I(t) in either ventricular or atrial cells. We conclude that the regulation of I(t) in ventricular cells is unique, rendering it extremely sensitive to temperature changes and to elevations in thyroxine levels. These results are discussed in the context of long-term regulation of ionic channels.
