Fig. 3. Dynamic action potential clamp experiments implementing heterologously expressed wild-type (WT) or mutant Na_v1.2 channels associated with early-infantile (EI) or later-onset (LO) SCN2A epilepsy.

In the axon initial segment (AIS) compartment model, the Na_v1.6 conductance (gNa_v1.6) was set to zero, whereas the potassium channel conductance (gK_v) was adjusted to 200% (gNa_v1.6 = 0, gK_v = 2, respectively), enabling a more efficient action potential (AP) repolarisation during firing compared to a gK_v setting of 1 (Supplementary Fig. 6). a Representative examples of AP firing in response to 4 and 10 pA step current stimuli. Note that each Na_v1.2 variant resulted in a unique firing profile relative to WT. b–e Input–output relationships demonstrating the effect of increasing stimulus strength on action potential frequency in the presence of Na_v1.2 channel variants (WT, black solid circle; mutants, colored open circles) associated with early-infantile (EI)-severe (b), EI-variable (c), EI-benign (d), or later-onset (LO) (e) SCN2A epilepsy. Firing was elicited by stimulus current steps in the range between −2 and 22 pA, in 2 pA increments. Data shown are mean ± SEM; n, the number of independent experiments between parentheses. Firing frequencies relative to WT were assessed using two-way ANOVA followed by Dunnett’s post-hoc test; asterisks indicate P < 0.05 (for individual P values see Supplementary Table 5). Note the decreased or increased rheobase with the EI-severe R1629L and later-onset D195G variants, respectively. The statistical evaluation of the action potential morphology is shown in Supplementary Table 6.