Abstract | BACKGROUND: Gain-of-function variants in the CACNA1C-encoded L-type calcium channel (LTCC, Cav1.2) cause type 8 long QT syndrome (LQT8). The pore region contains highly conserved glutamic acid (E) residues that collectively form the LTCC's selectivity filter. Here, we identified and characterized a pore-localizing missense variant, E1115K, that yielded a novel perturbation in the LTCC. OBJECTIVE: The purpose of this study was to determine whether CACNA1C-E1115K alters the LTCC's selectivity and is the substrate for the patient's LQTS. METHODS: The proband was a 14-year-old male with idiopathic QT prolongation and bradycardia. Genetic testing revealed a missense variant, CACNA1C-E1115K. The whole-cell patch clamp technique was used to measure CACNA1C-WT and -E1115K currents when heterologously expressed in TSA201 cells. RESULTS: The CACNA1C-E1115K channel exhibited no inward calcium current. Instead, robust cardiac transient outward potassium current (Ito)-like outward currents that were blocked significantly by nifedipine were measured when 2 mM/0.1 mM extracellular/intracellular CaCl2 or 4 mM/141 mM extracellular/intracellular KCl was applied. Furthermore, when 140 mM extracellular NaCl was applied, the CACNA1C-E1115K channel revealed both robust inward persistent Na+ currents with slower inactivation and outward currents, which were also nifedipine sensitive. In contrast, CACNA1C-WT revealed only a small inward persistent Na+ current without a robust outward current. CONCLUSION: This CACNA1C-E1115K variant destroyed the LTCC's calcium selectivity and instead converted the mutant channel into a channel with a marked increase in sodium-mediated inward currents and potassium-mediated outward currents. Despite the anticipated 50% reduction in LTCC, the creation of a new population of channels with accentuated inward and outward currents represents the likely pathogenic substrates for the patient's LQTS and arrhythmia phenotype.
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Authors | Dan Ye, David J Tester, Wei Zhou, John Papagiannis, Michael J Ackerman |
Journal | Heart rhythm
(Heart Rhythm)
Vol. 16
Issue 2
Pg. 270-278
(02 2019)
ISSN: 1556-3871 [Electronic] United States |
PMID | 30172029
(Publication Type: Case Reports, Journal Article, Research Support, Non-U.S. Gov't)
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Copyright | Copyright © 2018. Published by Elsevier Inc. |
Chemical References |
- CACNA1C protein, human
- Calcium Channels, L-Type
- DNA
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Topics |
- Adolescent
- Autism Spectrum Disorder
(genetics, metabolism)
- Bradycardia
(diagnosis, genetics, physiopathology)
- Calcium Channels, L-Type
(genetics, metabolism)
- Cells, Cultured
- DNA
(genetics)
- DNA Mutational Analysis
- Electrocardiography
- Humans
- Male
- Mutation, Missense
- Patch-Clamp Techniques
- Pedigree
- Romano-Ward Syndrome
(diagnosis, genetics, physiopathology)
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