Calcium Transients Closely Reflect Prolonged Action Potentials in iPSC Models of Inherited Cardiac Arrhythmia

Abstract

SummaryLong-QT syndrome mutations can cause syncope and sudden death by prolonging the cardiac action potential (AP). Ion channels affected by mutations are various, and the influences of cellular calcium cycling on LQTS cardiac events are unknown. To better understand LQTS arrhythmias, we performed current-clamp and intracellular calcium ([Ca2+]i) measurements on cardiomyocytes differentiated from patient-derived induced pluripotent stem cells (iPS-CM). In myocytes carrying an LQT2 mutation (HERG-A422T), APs and [Ca2+]i transients were prolonged in parallel. APs were abbreviated by nifedipine exposure and further lengthened upon releasing intracellularly stored Ca2+. Validating this model, control iPS-CM treated with HERG-blocking drugs recapitulated the LQT2 phenotype. In LQT3 iPS-CM, expressing NaV1.5-N406K, APs and [Ca2+]i transients were markedly prolonged. AP prolongation was sensitive to tetrodotoxin and to inhibiting Na+-Ca2+ exchange. These results suggest that LQTS mutations act partly on cytosolic Ca2+ cycling, potentially providing a basis for functionally targeted interventions regardless of the specific mutation site.

Calcium-Voltage Coupling in the Genesis of Early and Delayed Afterdepolarizations in Cardiac Myocytes

“…6 as well as previous experiments (sample voltage traces are shown in Fig. S3) (3,31,37). Note that in Fig.…”

Mexiletine rescues a mixed biophysical phenotype of the cardiac sodium channel arising from the SCN5A mutation, N406K, found in LQT3 patients

“…The SCN5A mutation N406K (asparagine replaced with lysine at position 406) was reported previously in two separate patients associated with LQT3 phenotype [9,10]. Both studies reported significantly prolonged QTc interval on surface ECG and increased late I Na in functional studies.…”

“…Spencer et al [10] discovered both action potentials and calcium transients were markerly prolonged in patient-derived induced pluripotent stem cells expressing SCN5A-N406K. The enhanced calcium transients were thought to account for the polymorphic ventricular tachycardia the patient has at birth.…”

Automated Video-Based Analysis of Contractility and Calcium Flux in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes Cultured over Different Spatial Scales

“…21 Briefly, 30 days after initiating differentiation with CHIR, visibly beating myocytes were dispersed by trypsinization onto fibronectin-coated coverslips (no. 1, CS15R; Warner Instruments).…”

“…23 Note, puromycin is driven by the endogenous AAVS1 promoter, to improve the fidelity of targeting. 21 iPSC lines containing the GCaMP6f cassette (GCaMP-WTC) were selected using puromycin (0.5 mg/mL). A heterozygous knockin clone was generated and differentiated into iPS-CM to check GCaMP6f functionality.…”