Abstract 2274: Rescue of a Misprocessed LQT3 Mutation in Mouse Heart
Introduction The SCN5A mutation resulting in L1825P (LP) has been associated with cisapride (Cis)-induced torsades de pointes. In CHO cells, LP channels show a prominent late current, reduced peak INa due to ER retention, and increased cell surface expression with Cis. We generated mice expressing flag-tagged LP and wild-type human (H) sodium channels in the murine Scn5a locus. Here we determined the effect of Cis on sodium channel function and cell surface expression in LP/H and H/H ventricular myocytes.
Methods and Results As previously reported, LP/H × LP/H matings produced only H/H and LP/H offspring, indicating that LP/LP is embryolethal. Peak INa (measured using Nao=5mM at −30 mV) was 6.8±0.8 pA/pF (LP/H, n=14) vs. 36.2±3.1 pA/pF (H/H, n=14). After exposure of isolated cells to Cis (5 μM × 2 hr), there was no change in H/H INa, but INa in LP/H myocytes increased ~100% (to 13.4±1.5 pA/pF, n=12, p<0.01); vehicle had no effect. Immunostaining revealed a markedly increased flag (LP) signal at the intercalated disk after Cis. To quantify both window and late currents, we used a 2-s ramp from −120 to +40 mV in Nao=135 mM. Under these conditions (figure⇓), LP/H myocytes displayed marked increases in both window (−70 mV) and late (−20 mV) currents.
L1825P mice display striking reduction in peak sodium current with increased window and late currents.
These data demonstrate for the first time that drug intervention can rescue cell surface expression of a misprocessed mutant cardiac ion channel in a transgenic model that recapitulates the clinical phenotype.