Abstract 17670: Common Polymorphism RYR2-Q2958R Increases Spontaneous Calcium Release Under Stress and May be Associated With Increased Risk of Sudden Cardiac Death
Background: The calcium release channel/ryanodine receptor (RyR2) provides the majority of Ca2+ for contraction of cardiac cells. RyR2 malfunction precipitates Ca2+-mediated arrhythmias and hypertrophic cardiomyopathy (HCM). Although RyR2-Q2958R is a common RyR2 polymorphism, the role of RyR2-Q2958R as a potential pro-arrhythmic modifier remains unknown.
Methods and Results: High-throughput genotyping of the Q2958R polymorphism revealed that the minor allele frequency for R2958 was greatest in Caucasians, followed by Mexican-Americans, Italians, and African-Americans. In addition, the presence of two minor alleles (RR2958) was associated with sudden cardiac death in an HCM cohort study. Site-directed mutagenesis was used to introduce the Q2958R mutation in the mouse ryr2 gene. Compared to wild type (Q2958), R2958 channels produced early and depressed Ca2+ transients under increasing external [Ca2+] when expressed in HEK-293cells. Cytosolic Ca2+ sensitivity of R2958 channels was unaltered as their Ca-dependence of [3H]ryanodine binding was identical to that of WT, but single channel recordings demonstrated higher open probability for R2958 channels in response to increasing luminal [Ca2+]. Homologous recombination was used to generate a knock-in mouse bearing the RyR2-Q2958R polymorphism. Hearts from heterozygous (Q2958R) or homozygous (RR2958) mice showed no gross structural alterations and their cytosolic Ca2+-dependence of [3H]ryanodine binding curves were not different from WT (QQ2958), in line with the results obtained using recombinant protein. However, Ca2+-imaging of isolated ventricular cardiomyocytes subjected to a “stress” protocol that loaded the SR with Ca2+ (5-sec train of stimulations at 3 Hz under 300 nM Isoproterenol) demonstrated that homozygous and heterozygous cells developed spontaneous Ca2+ release (SCR) events with higher frequency than WT (RR2958: 93 SCRs in 34 cells; Q2958R: 32 SCRs in 12 cells; WT: 11 SCRs in 13 cells).
Conclusions: RyR2-Q2958R is found variably in different ethnicities and increases SCR under conditions of Ca2+ overload, such as during β-adrenergic stimulation. It is conceivable that the RyR2-Q2958R polymorphism may predispose some HCM patients to sudden cardiac death.
- © 2013 by American Heart Association, Inc.