Divergent Effects of Disease-Associated Mutations on Type 2 Ryanodine Receptor Channel

Abstract

Type 2 ryanodine receptor (RyR2) is a Ca2+ release channel in the sarcoplasmic reticulum and plays a pivotal role in excitation-contraction coupling in heart. RyR2 is the major target for arrhythmogenic diseases, e.g., catecholaminergic polymorphic ventricular tachycardia (CPVT) and arrhythmogenic right ventricular cardiomyopathy (ARVC). To date, over 150 mutations have been identified in the RyR2 gene of CPVT and ARVC patients. It is widely believed that CPVT and ARVC mutations cause hyperactivation of the Ca2+-induced Ca2+ release (CICR), resulting in abnormal Ca2+ homeostasis in cardiac muscle. CICR shows biphasic Ca2+ dependence against cytoplasmic Ca2+, thus the activity can be determined by three parameters: sensitivity to activating Ca2+, sensitivity to inactivating Ca2+, and the gain (i.e., peak activity). In addition, CICR is also regulated by luminal Ca2+; high luminal Ca2+ activates CICR, and vise versa. However, it remains unclear how the disease-associated mutations affect these parameters. In this study, we expressed RyR2 channels carrying several CPVT/ARVC mutations in HEK cells and tested their CICR by live-cell Ca2+ imaging and [3H]ryanodine binding. Our results suggest that the disease-associated mutations divergently affects the parameters of CICR depending on the sites for mutation. The underlying molecular mechanism will be discussed.