# Calmodulin D133H Disrupts Cav1.2 and Kv7.1 Regulation to Prolong Cardiac Action Potentials in Long QT Syndrome

## TL;DR

A calmodulin mutation disrupts calcium and potassium channels in the heart, leading to prolonged electrical signals and arrhythmias in Long QT syndrome.

## Contribution

The study reveals how the D133H calmodulin variant affects both Cav1.2 and Kv7.1 channels, linking them to cardiac arrhythmias.

## Key findings

- D133H reduces Ca2+ affinity and disrupts Ca2+-dependent inactivation of Cav1.2.
- D133H decreases Kv7.1 activation, limiting repolarizing K+ currents.
- These effects prolong cardiac action potentials and contribute to arrhythmogenesis in Long QT syndrome.

## Abstract

What are the main findings?

The calmodulin variant D133H disrupts Ca2+-dependent inactivation of Cav1.2 and reduces activation of Kv7.1.D133H reduces Ca2+ affinity and alters interactions with Cav1.2 and Kv7.1 binding domains.

The calmodulin variant D133H disrupts Ca2+-dependent inactivation of Cav1.2 and reduces activation of Kv7.1.

D133H reduces Ca2+ affinity and alters interactions with Cav1.2 and Kv7.1 binding domains.

What are the implications of the main findings?

The dual impact on Cav1.2 and Kv7.1 reveals cross-channel regulatory coupling as a key determinant of ventricular repolarisation.These mechanistic insights broaden understanding of how specific CaM variants remodel cardiac electrical signalling in Long QT syndrome.

The dual impact on Cav1.2 and Kv7.1 reveals cross-channel regulatory coupling as a key determinant of ventricular repolarisation.

These mechanistic insights broaden understanding of how specific CaM variants remodel cardiac electrical signalling in Long QT syndrome.

Calmodulin (CaM) plays a central role in cardiac excitation–contraction coupling by regulating ion channels, including the L-type calcium (Ca2+) channel Cav1.2 and the voltage-gated potassium (K+) channel Kv7.1. Mutations in CaM are linked to severe arrhythmogenic disorders such as Long QT syndrome (LQTS), yet the molecular mechanisms remain incompletely understood. Here, we investigate the structural and functional consequences of the arrhythmia-associated CaM variant D133H. Biophysical analysis revealed that D133H destabilises Ca2+ binding at the C-terminal lobe of CaM, altering its Ca2+-dependent conformational changes. Electrophysiological recordings demonstrated that CaM D133H impairs Ca2+-dependent inactivation (CDI) of Cav1.2, prolonging Ca2+ influx, while also reducing activation of Kv7.1, thereby limiting repolarising K+ currents. Together, these dual defects converge to prolong action potential duration, providing a mechanistic basis for arrhythmogenesis in LQTS. Our findings establish that CaM D133H perturbs both Ca2+ and K+ channel regulation, highlighting a shared pathway by which calmodulinopathy mutations disrupt cardiac excitability.