Fig. 3.

Na_vβ₁ and Na_vβ₂ subunits modulate late Na⁺ current (I_NaL) decay kinetics and density in ventricular cardiac myocytes from both normal dogs and from dogs with chronic heart failure. Shown are results of post-transcriptional silencing of SCN1B and SCN2B genes with the corresponding siRNAs. A: representative raw traces of I_NaL were recorded in cells from the normal (top) and failing (bottom) hearts cultured for 5 days after transfection with the control nonsilencing siRNA (control) and with Na_vβ₁-siRNA or Na_vβ₂-siRNA (indicated by the arrows), respectively. Exponential fits (Supplemental Eq. S1) are shown by solid lines and are superimposed with the experimental traces. Bottom, inset: voltage protocol. Statistical data for current density (B), and decay time constants (C and D) evaluated by the double exponential fit (Supplemental Eq. S1) in freshly isolated myocytes and after 5 days in culture of normal hearts, in freshly isolated myocytes of failing dog hearts and after 5 days in culture infected by the nonsilencing (ns-siRNA) or silencing siRNA, respectively, are shown. There was no statistically significant difference between I_NaL parameters when freshly isolated and cultured myocytes were compared for both normal and failing hearts. All I_NaL parameters remain significantly different when normal and failing hearts were compared for both freshly isolated and cultured cells infected by the ns-siRNA (*, §). Infection of myocytes of normal and failing heart with adenovirus containing Na_vβ₁- or Na_vβ₂-siRNA caused statistically significant (**, ¶) reduction or increase (†, ‡) in the I_NaL density (B) or decay time constants for both normal and failing hearts, respectively. Statistical significance, P < 0.05, was evaluated by the ANOVA followed by Bonferroni's post hoc test. Data represent means ± SE; cell numbers are indicated at the bars.