Abstract 17783: Calmodulin Mutants Associated With Long QT Syndrome Suppress Inactivation of Cardiac L-type Ca2+ Currents and Prolong Action Potentials in Guinea-Pig Ventricular Myocytes
Background: Calmodulin (CaM) mutations have recently been identified in infants with severe long QT syndrome (LQTS), frequent T-wave alternans, and recurrent cardiac arrest. Yet, the underlying mechanisms are unknown. The mutations, residing in or nearby Ca2+ binding loops of CaM, impair Ca2+ binding; and the CaM-dependent inactivation (CDI) of cardiac L-type Ca2+ channels (LTCCs) potently regulates action potential duration (APD). Here, we investigated the effect of CaM mutants (D130G, D96V, and F142L) on native LTCCs and action potentials in acutely dissociated adult guinea-pig ventricular myocytes (aGPVMs).
Method: aGPVMs were transduced with adenovirus bearing genes encoding wild type (WT) and mutant CaMs. Whole-cell LTCC currents and action potentials (APs) were measured within 36 hours of cell isolation.
Results: Panel A displays the control CDI profile of LTCCs, recorded in myocytes overexpressing WT CaM. Ca2+ current (black) decayed more rapidly than Ba2+ current (gray), indicating the presence of robust CDI (no difference in myocytes without adenoviral expression). By contrast, all three CaM mutants strongly diminished CDI; this is illustrated for the D96V CaM mutant, where Ca2+ current (A, red) now decays as slowly as Ba2+ current (gray). This striking reduction in CDI corresponds to extreme prolongation of APD (B, C). Panel B displays one example where a myocyte expressing WT CaM exhibits typical APs (gray), whereas expression of D96V CaM yields APDs > 2s (black). In other cells, APD prolongation was accompanied by repolarization alternans (C). These effects provide a plausible molecular mechanism for severe LQTS and ventricular arrhythmias.
Conclusion: Expression of CaM mutants D130G, D96V, and F142L markedly suppress CDI of native LTCCs, which is likely to contribute strongly to severe APD prolongation, with attendant QTc changes in patients with these mutations.
- © 2013 by American Heart Association, Inc.