Arrhythmogenic calmodulin mutations disrupt intracellular cardiomyocyte Ca2+ regulation by distinct mechanisms

Area of Science:

• Cardiovascular Physiology
• Molecular Cardiology
• Genetics of Arrhythmias

Background:

• Calmodulin (CaM) mutations are linked to congenital long QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardia (CPVT).
• Mechanisms underlying these distinct arrhythmia syndromes due to CaM mutations remain unclear.
• Investigating CaM's role in cardiomyocyte calcium (Ca2+) homeostasis is crucial for understanding arrhythmia pathogenesis.

Purpose of the Study:

• To test if LQTS-associated CaM mutants disrupt Ca2+ homeostasis in cardiomyocytes.
• To determine if CaM mutations affect late Na+ current or Ca2+-dependent inactivation of L-type Ca2+ current.
• To differentiate the molecular mechanisms of LQTS and CPVT associated with CaM mutations.

Main Methods:

• Coexpression of CaM mutants with the human cardiac NaV1.5 channel in tsA201 cells.
• Investigation of LQTS- and CPVT-associated CaM mutations in mammalian fetal ventricular cardiomyocytes.
• Electrophysiological recordings to assess L-type Ca2+ current and Ca2+-dependent inactivation.

Main Results:

• LQTS-associated CaM mutants impaired Ca2+-dependent inactivation of L-type Ca2+ current, while CPVT-CaM mutants showed no effect.
• LQTS-CaM mutants led to loss of Ca2+-transient entrainment, with varying severity based on CaM affinity.
• CaV1.5 channel function was not consistently affected by LQTS-CaM mutants, ruling out its direct contribution to LQTS pathogenesis.

Conclusions:

• Calmodulin mutations linked to LQTS primarily affect Ca2+-dependent inactivation of L-type Ca2+ current.
• These CaM mutations do not appear to significantly impact L-type Na+ current in LQTS.
• Understanding these distinct CaM mutation effects provides insight into divergent arrhythmia mechanisms.