Long QT Syndrome (LQTS) is a life-threatening cardiac channelopathy primarily caused by mutations in the KCNQ1 gene, leading to dysfunction of the KV7.1/KCNE1 channel complex, essential for proper repolarization of the ventricular action potential. These mutations predispose individuals to prolonged QT intervals and increased risk of arrhythmia. Despite current treatment options, such as β-blockers, these therapies do not address the root cause of the disease, and up to 30% of individuals remain at risk for cardiac events. Moreover, the clinical phenotypes of genotype-positive patients vary considerably, suggesting that factors beyond the primary mutation play a significant role. One possible explanation is the presence of endogenous compounds that modulate the KV7.1/KCNE1 channel.

This thesis investigates the potential role of endocannabinoid compounds, which have emerged as key players in cardiovascular function, in modulating the KV7.1/KCNE1 channel. The primary technique employed in this thesis is the Two-electrode voltage clamp (TEVC) performed in Xenopus laevis oocytes expressing wild-type or mutated KV7.1/KCNE1 channels. Complementary Molecular Dynamic simulations were conducted to further explore the mechanism of action of these compounds. In addition, other electrophysiological techniques, including Automated and Manual Patch-clamp and Langendorff experiments, were used to assess the translational potential of these compounds in more complex systems.

We demonstrated that endocannabinoids with a Serine head group, which are negatively charged at physiological pH, facilitate the activation of wild-type KV7.1/KCNE1 by interacting with KV7.1 at two distinct sites, resulting in a shift in voltage dependence to a negative direction along the voltage axis, and increase of maximal conductance. Furthermore, we showed that the endocannabinoid N-arachidonoyl-L-Serine (ARA-S) effectively activates a broad range of LQTS-associated KV7.1 mutants, even when its primary binding site is altered, with varying concentrations required to restore mutant channels to a wild-type-like behavior. The translational relevance of these findings is highlighted by the maintained effects of ARA-S in KV7.1/KCNE1 when expressed in mammalian cell lines and by shortening of the action potential duration in LQTS rabbit cardiomyocytes and a drug-induced LQTS model of isolated guinea pig hearts. Moreover, the development of synthetic endocannabinoids with structural tail modifications demonstrated potential for identifying novel activators of KV7.1/KCNE1.

These findings highlight endocannabinoids as potential protective factors in LQTS, opening new possibilities for clinical management and therapeutic development.