Thyroid stimulating hormone directly modulates cardiac electrical activity.

Area of Science:

• Cardiology
• Endocrinology
• Molecular Biology

Background:

• Hypothyroidism causes cardiac repolarization abnormalities, linked to altered ion currents.
• The role of thyroid hormones (T3, T4) versus TSH in these changes is debated.
• Elevated TSH levels correlate with repolarization issues in hypothyroid patients.

Purpose of the Study:

• To investigate the direct impact of TSH on cardiac electrical properties.
• To determine if TSH affects specific ion currents involved in cardiac repolarization.

Main Methods:

• Action potential and ion channel mRNA expression recorded from adult rat left ventricles.
• Patch-clamp technique used to record repolarizing K(+) currents and L-type Ca(2+) current (ICa-L) in isolated ventricular myocytes.
• Experimental exposure to TSH.

Main Results:

• TSH exposure prolonged action potential duration and slightly depolarized resting membrane potential.
• TSH activation reduced the amplitude of Ito and IK1 currents, linked to decreased channel expression.
• TSH did not affect ICa-L, IK, or IKur.

Conclusions:

• TSH directly impacts cardiac electrical activity by reducing Ito and IK1 currents.
• These TSH-induced changes may explain some cardiac repolarization disturbances observed in hypothyroidism.
• The findings suggest elevated TSH, not just low T3, contributes to cardiac issues in hypothyroidism.