Abstract 1240: Sodium Channel Splice Variants Seen in Human Heart Failure Result in Dominant Negative Suppression of the Wild-Type Current
Patients with heart failure have increased risk of death and reduced Na+ channels. We have identified a possible mechanism whereby Na+ channels are decreased in human heart failure. We have observed that heart failure is associated with increases of 14.2 fold and 3.8 fold in two (C and D) of three cardiac Na+ channel mRNA splice variants. These variants encode for channels that are truncated before the domain IV pore-forming loop and are predicted to be non-functional. We tested this prediction by expressing the truncated forms in HEK cells. The truncated SCN5A cDNAs labeled either with IRES (internal ribosome entry site)-mediated GFP or fused GFP were transitively transfected into HEK cells or a HEK cell line stably expressing the native human SCN5A. HEK cell lines stably expressing the truncation variants were created by selection for three weeks with geneticin after transfection. Neither of the two truncations generated current when transfected alone. When transfected in a cell line stably expressing wild-type Na+ channels, the presence of the truncations resulted in 54.6% (±8.5, p<0.01, N=14) and 56.0% (±8.9, p<0.01, N=10) reductions in peak current with the C and D variants respectively when compared to the wild-type alone. The reduction of wild-type current in the presence of the truncations showed variant dose-dependency when varying the amount of vector encoding for the splice variants. Laser fluorescent scanning for N-terminal GFP labeled Na+ channels confirmed a reduced number of wild-type channels in the membrane in the presence of mRNA for the two truncations. In conclusion, truncated Na+ channel mRNA splice variants are increased in human heart failure. These truncations have a dominant negative effect on the wild-type allele. This may help explain the reduced Na+ current and increased arrhythmic risk in heart failure.