Characterization of an N-terminal Nav1.5 channel variant – a potential risk factor for arrhythmias and sudden death?

Fig. 1. Detection of the SCN5A variant p.(Ser106Gly) in a patient with aborted cardiac arrest. a Schematic representation of the Nav1.5 channel and localization of the detected N-terminal variant. b Alignment of a partial N-terminal sequence among mammals. The affected amino acid is indicated in red. c Assessment of the genetic variant by in silico prediction tools

Fig. 2. ECG findings of the patient. a ECG taken 1 year previous to the cardiac event is showing sinus rhythm with a heart rate of 66/min, flat P waves, PR interval 140 ms, QRS 100 ms, T inversion in lead III and QTc of 389 ms. b ECG from approximately 3 months after cardiac event under beta-blocker therapy is showing sinus bradycardia with a heart rate of 38/min, flat P waves, PR interval 190 ms, QRS 110 ms and QTc of 365 ms

Fig. 3. Nav1.5 S106G results in gain of function. a Typical Na+ currents in HEK293 cells transiently expressing NaV1.5 WT (top) or NaV1.5-S106G mutant (down). Currents were elicited by clamping cells from holding voltage (− 140 mV, 100 mS) to test voltages (between + 50 mV and − 100 mV, 100 ms) and back to post clamp voltage (− 140 mV, 100 ms). b Mean current density/voltage relationships (±SE) from cells transfected with WT (black, n = 9) or S106G mutant (red, n = 8). c Peak currents at − 25 mV from (b) for WT (black) mutant (red) and data from cells co-transfected with WT and S106G mutant (blue, n = 12). d Boltzmann fits of voltage-dependent inactivation (left) and activation (right) for Nav1.5 WT (black/grey) and NavS106G mutant (red/brown). The mutation causes a positive shift in the V1/2 value for inactivation (− 88.2 ± 0.8 mV versus 91.5 ± 1 mV) and a negative shift of the V1/2 value for activation (− 45.3 ± 0.9 mV versus − 39.9 ± 0.8 mV). The P value for a difference between V1/2 values of the WT and mutant < 0.05. Inset: estimated window currents for WT and mutant from (b). The colors of the line correspond to those in (c)

Fig. 4. S106G mutation does not affect unitary channel conductance. a Exemplary recordings of a HEK293 cell expressing the Nav1.5 WT channel for noise analysis. Channels were activated 200 times by stepping membrane from holding voltage (1–40 mV, 100 ms) to test voltage of − 20 mV (100 ms). Red arrows delimit the part of the traces used for the analysis. b Example of noise analysis from one cell expressing Nav1.5 WT channel. The variance between pulses is plotted as a function of the mean current value. The data were fitted with parabolic function (Eq. 5) yielding the unitary channel conductance from the initial slope of the fit. c Average i values (mean ± SE) for WT and S106G channels at two different voltages: − 20 mV (WT n = 3, black; S106G n = 4, red) and − 40 mV (WT n = 4, black; S106G n = 4, red)