Abstract
FUNDING ACKNOWLEDGEMENTS: Type of funding sources: None. BACKGROUND: The cardiac sodium channel Nav1.5 is transported to the membrane by the microtubule network. Alterations in microtubule dynamics are known to impact on ion channel trafficking. Pathophysiological conditions such as heart failure and Duchenne muscular dystrophy (DMD) are associated with an increase in microtubule detyrosination as well as a decreased sodium current (INa) and pro-arrhythmia. Parthenolide, a compound that decreases the fraction of detyrosinated microtubules, has been shown to have beneficial effects on cardiac function in DMD mice, but its impact on INa has not been investigated. METHODS AND RESULTS: Cardiomyocytes (CMs) from wild type (WT) and mdx (DMD) mice were used to investigate the effect of parthenolide. Cells were incubated with either 10 µM parthenolide or DMSO for 3-5 hours. INa and action potential (AP) characteristics were assessed using the patch-clamp technique, while immunofluorescence and stochastic optical reconstruction microscopy (STORM), were used to investigate microtubule detyrosination and Nav1.5 cluster density, respectively. In accordance with previous studies, we observed increased levels of detyrosinated microtubules and decreased INa in mdx CMs compared to WT. Treatment with parthenolide decreased the fraction of detyrosinated microtubules and significantly increased INa magnitude in mdx CMs, but had no effect on INa in WT CMs. Accordingly, parthenolide significantly increased AP maximal upstroke velocity in mdx CMs, without affecting other AP properties. Parthenolide did not affect INa gating properties, indicating that it increased INa by enhancing Nav1.5 membrane trafficking. Indeed, STORM analysis showed that parthenolide increased Nav1.5 cluster density at both the lateral membrane (crest) and intercalated disc region in mdx CMs while it had no effect on WT CMs. CONCLUSIONS: Parthenolide restores INa and Nav1.5 membrane expression in mdx CMs, and may be of potential benefit in other pathophysiological conditions associated with increased microtubule detyrosination and reduced INa. Further elucidation of the impact of microtubule dynamics on Nav1.5 may identify additional therapeutic targets for restoring conduction and preventing arrhythmias.