Differential Thermosensitivity in Nav1.5 Mutations Associated with Long QT and Brugada Syndromes

Abstract

Some cardiac arrhythmias are associated with mutations in the cardiac voltage-gated sodium channel (NaV1.5), including long QT3 syndrome (gain-of-function mutations) and Brugada syndrome (loss-of-function mutations). Two mutations, E1784K and R1193Q are associated with both syndromes, whereas R376H is a Brugada syndrome mutation. We tested the effects of temperature on gating in wild-type (WT) NaV1.5 and these three mutations. Whole-cell patch clamp experiments were performed on CHO cells transiently transfected with the NaV1.5 α−subunit, the β1-subunit, and eGFP. Voltage-clamp protocols were performed at either 10 °C, 22 °C, or 34 °C. Conductance in WT was not temperature dependent compared to the mutant channels, all of which showed a depolarizing shift in the midpoint of the conductance curve at 10°C. A significant hyperpolarizing shift in steady-state fast inactivation was seen when temperature increased to 34 °C in R1193Q. In WT and R376H, persistent current was greater at 10 oC than at 22 oC. In contrast, persistent current both R1193Q and E1784K had U-shaped temperature dependence in which persistent current increased when temperature was changed from 22 °C to 34 °C and from 22 oC to 10 oC. E1784K and R376H had greater use-dependent inactivation with increasing temperatures (22 °C to 34 °C), whereas use-dependent inactivation in R1193Q had no thermosensitivity. This is consistent with previous results, which show that both the E1784K and R1193Q are mixed syndrome mutations. Although elevated temperatures may trigger long QT syndrome, the large stabilization in fast inactivation for R1193Q and the increase in use-dependence for E1784K suggest a mixed syndrome phenotypic expression. The loss of function in R376H, associated with Brugada-syndrome, is exacerbated by elevated temperature. In summary, these results suggest temperature fluctuations could be a trigger for long-QT and Brugada related arrhythmias.