RESUMO
BACKGROUND/AIMS: Induced pluripotent stem (iPS) cells generated from accessible adult cells of patients with genetic diseases open unprecedented opportunities for exploring the pathophysiology of human diseases in vitro. Catecholaminergic polymorphic ventricular tachycardia type 1 (CPVT1) is an inherited cardiac disorder that is caused by mutations in the cardiac ryanodine receptor type 2 gene (RYR2) and is characterized by stress-induced ventricular arrhythmia that can lead to sudden cardiac death in young individuals. The aim of this study was to generate iPS cells from a patient with CPVT1 and determine whether iPS cell-derived cardiomyocytes carrying patient specific RYR2 mutation recapitulate the disease phenotype in vitro. METHODS: iPS cells were derived from dermal fibroblasts of healthy donors and a patient with CPVT1 carrying the novel heterozygous autosomal dominant mutation p.F2483I in the RYR2. Functional properties of iPS cell derived-cardiomyocytes were analyzed by using whole-cell current and voltage clamp and calcium imaging techniques. RESULTS: Patch-clamp recordings revealed arrhythmias and delayed afterdepolarizations (DADs) after catecholaminergic stimulation of CPVT1-iPS cell-derived cardiomyocytes. Calcium imaging studies showed that, compared to healthy cardiomyocytes, CPVT1-cardiomyocytes exhibit higher amplitudes and longer durations of spontaneous Ca(2+) release events at basal state. In addition, in CPVT1-cardiomyocytes the Ca(2+)-induced Ca(2+)-release events continued after repolarization and were abolished by increasing the cytosolic cAMP levels with forskolin. CONCLUSION: This study demonstrates the suitability of iPS cells in modeling RYR2-related cardiac disorders in vitro and opens new opportunities for investigating the disease mechanism in vitro, developing new drugs, predicting their toxicity, and optimizing current treatment strategies.
Assuntos
Células-Tronco Pluripotentes Induzidas/metabolismo , Modelos Biológicos , Canal de Liberação de Cálcio do Receptor de Rianodina/metabolismo , Potenciais de Ação , Cálcio/metabolismo , Catecolaminas/metabolismo , Diferenciação Celular , Colforsina/metabolismo , AMP Cíclico/metabolismo , Eletrocardiografia , Heterozigoto , Humanos , Células-Tronco Pluripotentes Induzidas/citologia , Cariotipagem , Mutação , Miócitos Cardíacos/citologia , Miócitos Cardíacos/metabolismo , Técnicas de Patch-Clamp , Fenótipo , Canal de Liberação de Cálcio do Receptor de Rianodina/genética , Taquicardia Ventricular/metabolismo , Taquicardia Ventricular/patologiaRESUMO
The view that Ca(2+) entry through voltage-dependent Ca(2+) channels (VDCC) and through nicotinic receptors for acetylcholine (nAChRs) causes equal catecholamine release responses in chromaffin cells, was reinvestigated here using new protocols. We have made two-step experiments consisting in an ACh prepulse followed by a depolarizing pulse (DP). In voltage-clamped bovine chromaffin cells an ACh prepulse caused a slow-rate release but augmented 4.5-fold the much faster exocytotic response triggered by a subsequent depolarizing pulse (measured with capacitance and amperometry). If the ACh prepulse was given with mecamylamine or in low external Ca(2+), the secretion increase disappeared. This suggests a two-step model for the effects of ACh: (1) meager Ca(2+) entry through nAChRs mostly serves to keep loaded with vesicles the secretory machine; and (2) in this manner, the cell is prepared to respond with an explosive secretion of catecholamine upon depolarization and fast high Ca(2+) entry through VDCC.
