Figure 3.

Post-transcriptional SCN5A gene silencing results in functional reduction of the transient Na⁺ current, I_NaT, and reveals non-cardiac Na⁺ channel component in LV cardiomyocytes from dog with chronic heart failure

A, representative raw traces of I_NaT were recorded at different membrane potentials (V_m) in cells 5 days after infection with virus containing control non-silencing siRNA and cDNA for GFP (control GFP, left), and siRNA-Na_v1.5 (right). Cell images expressing GFP are shown in insets. B, average data from peak I_NaT–voltage relationship obtained in cultured cells for 5 days with virally delivered control siRNA (• control GFP, n = 6), and Na_v1.5-siRNA (▴, n = 7). We found a statistically significant reduction of I_NaT in response to Na_v1.5-siRNA in a wide range of potentials (*). Continuous lines show theoretical curves fitted to experimental current–voltage (I–V) data points to evaluate the steady-state activation (SSA) parameters which are given in the panel. •, control GFP, control siRNA (n = 18); ▴, Na_v1.5-siRNA (n = 16). C, average experimental data of steady-state inactivation (SSI) data points in control (•, n = 17) and after SCN5A gene silencing by the siRNA (▴, n = 16) along with the fit to a Boltzmann function. The F test revealed a statistically significant (P < 0.05) difference between theoretical fits (B and C), and statistical significance, P < 0.05, between experimental data points presented as mean ± SEM (B) was evaluated by ANOVA followed by Bonferroni's post hoc test. Voltage clamp protocols are shown in B and C insets; V_h, holding and V_p, pre-pulse potentials, respectively.