title: Calmodulin mutations associated with long QT syndrome prevent inactivation of cardiac L-type Ca(2+) currents and promote proarrhythmic behavior in ventricular myocytes.
abstract: Recent work has identified missense mutations in calmodulin (CaM) that are associated with severe early-onset long-QT syndrome (LQTS), leading to the proposition that altered CaM function may contribute to the molecular etiology of this subset of LQTS. To date, however, no experimental evidence has established these mutations as directly causative of LQTS substrates, nor have the molecular targets of CaM mutants been identified. Here, therefore, we test whether expression of CaM mutants in adult guinea-pig ventricular myocytes (aGPVM) induces action-potential prolongation, and whether affiliated alterations in the Ca(2+) regulation of L-type Ca(2+) channels (LTCC) might contribute to such prolongation. In particular, we first overexpressed CaM mutants in aGPVMs, and observed both increased action potential duration (APD) and heightened Ca(2+) transients. Next, we demonstrated that all LQTS CaM mutants have the potential to strongly suppress Ca(2+)/CaM-dependent inactivation (CDI) of LTCCs, whether channels were heterologously expressed in HEK293 cells, or present in native form within myocytes. This attenuation of CDI is predicted to promote action-potential prolongation and boost Ca(2+) influx. Finally, we demonstrated how a small fraction of LQTS CaM mutants (as in heterozygous patients) would nonetheless suffice to substantially diminish CDI, and derange electrical and Ca(2+) profiles. In all, these results highlight LTCCs as a molecular locus for understanding and treating CaM-related LQTS in this group of patients.
authors.affiliation: Calcium Signals Laboratory, Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, MD 21205.
authors.forename: Worawan B
authors.initials: WB
authors.lastname: Limpitikul
authors.affiliation: Calcium Signals Laboratory, Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, MD 21205.
authors.forename: Ivy E
authors.initials: IE
authors.lastname: Dick
authors.affiliation: Calcium Signals Laboratory, Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, MD 21205.
authors.forename: Rosy
authors.initials: R
authors.lastname: Joshi-Mukherjee
authors.affiliation: Department of Biotechnology, Chemistry and Environmental Engineering, Aalborg University, Denmark.
authors.forename: Michael T
authors.initials: MT
authors.lastname: Overgaard
authors.affiliation: Department of Medicine, Vanderbilt University, Nashville, TN 37232, USA; Department of Pharmacology, Vanderbilt University, Nashville, TN 37232, USA.
authors.forename: Alfred L
authors.initials: AL
authors.lastname: George
authors.affiliation: Calcium Signals Laboratory, Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Baltimore, MD 21205; Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205. Electronic address: dyue@jhmi.edu.
authors.forename: David T
authors.initials: DT
authors.lastname: Yue
mesh_terms: D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000235:genetics* / Q000378:metabolism; D002147:Calmodulin / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D006168:Guinea Pigs; D057809:HEK293 Cells; D006352:Heart Ventricles / Q000378:metabolism / Q000503:physiopathology; D006801:Humans; D008133:Long QT Syndrome / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D009154:Mutation; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000473:pathology; D018408:Patch-Clamp Techniques; D015398:Signal Transduction
chemical_list: D020746:Calcium Channels, L-Type; D002147:Calmodulin; D002118:Calcium
keywords: APD prolongation; Ca(2+)/CaM-dependent inactivation (CDI); Calmodulin; L-type Ca(2+) channel; Long-QT syndrome