The ryanodine receptor store-sensing gate controls Ca2+ waves and Ca2+-triggered arrhythmias

Abstract

Spontaneous Ca2+ release from intracellular stores is important for various physiological and pathological processes. In cardiac muscle cells, spontaneous store overload-induced Ca2+ release (SOICR) can result in Ca2+ waves, a major cause of ventricular tachyarrhythmias (VTs) and sudden death. The molecular mechanism underlying SOICR has been a mystery for decades. Here, we show that a point mutation E4872A in the helix bundle crossing (the proposed gate) of the cardiac ryanodine receptor (RyR2) completely abolishes luminal, but not cytosolic, RyR2 Ca2+ activation. Introducing metal-binding histidines at this site converts RyR2 into a luminal Ni2+ gated channel. Mouse hearts harboring an RyR2 mutation at this site (E4872Q+/−) are resistant to store overload-induced Ca2+ waves and completely protected against Ca2+-triggered VTs. These data show that the RyR2 gate directly senses store Ca2+, explaining RyR2 store Ca2+ regulation, Ca2+ wave initiation, and Ca2+-triggered arrhythmias. This novel store-sensing gate structure is conserved in all RyRs and inositol 1,4,5-trisphosphate receptors.

Endoplasmic Reticulum Stress and Ca2+ Depletion Differentially Modulate the Sterol Regulatory Protein PCSK9 to Control Lipid Metabolism

“…Specifically, the gain-of-function (GOF) RYR2 mutants (Q4201R and V4653F) yield increased ER Ca 2ϩ leakage, whereas the loss-of-function (LOF) RYR2 mutant (A4860G) exhibits reduced Ca 2ϩ leak into the cytosol as compared with WT RYR2 (6,42). Consistent with the effect of TG and A23, GOF RYR2 mutants induced PCSK9 expression (Fig.…”

“…F, to determine the effect of ER stress-inducing conditions via non-pharmacologic means on PCSK9 expression, HuH7 cells were exposed to medium deficient in either Ca 2ϩ , glucose, amino acids, or sterol for 24 h. G, in addition, the role of ER Ca 2ϩ loss on PCSK9 expression was examined using HEK293 cells that stably overexpress tetracycline-inducible GOF or LOF RYR2 mutants using immunoblots. GOF RYR2 mutant cell lines (Q4201R and V4653F) exhibit increased ER Ca 2ϩ leakage, whereas LOF RYR2 mutant (A4860G) exhibits reduced ER Ca 2ϩ leak compared to WT cells (6,42). Differences between treatments were assessed with paired Student's t tests, and all values are represented as mean Ϯ S.D.…”

“…The ability of the ER to mediate protein folding relies on the oxidative state and elevated Ca 2ϩ concentration of the ER (Ϸ400 M) relative to the cytosol (Ϸ100 nM) (4,5). An equilibrium formed between ER Ca 2ϩ uptake via sarco/endoplasmic reticulum ATPase and ER Ca 2ϩ release mediated by two homologous classes of intracellular Ca 2ϩ release channels, known as the ryanodine receptors (RYRs) and the inositol 1,4,5-triphosphate receptors, play a major role in the regulation of ER Ca 2ϩ homeostasis (6). Additional regulators of ER Ca 2ϩ homeostasis include ER luminal proteins that interact with Ca 2ϩ , such as buffer proteins and chaperones.…”

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

“…However, the homogeneous model appears to capture most of the experimentally observed behaviors, and in addition provides a key framework for future exploration of the role of heterogeneity. The RyR model developed by Restrepo et al (14) incorporated calsequestrin-mediated SR luminal Ca regulation, whereas recent experiments have demonstrated a luminal Ca-sensing site in the RyR mediating this effect (63). Moreover, the refractoriness of Ca release is controversial, with a wide range of experimentally measured values (64)(65)(66)(67)(68)(69) and different proposed causes.…”

Real-time intra-store confocal Ca2+ imaging in isolated mouse cardiomyocytes

“…RyRs have been proposed to sense the Ca 2+ concentration inside the SR via an allosteric signal involving calsequestrin, triadin and junctin [12]. Recently, it has been shown that the RyRs can also sense the Ca 2+ concentration inside the SR directly [13,14]. Alterations of the free SR Ca 2+ concentration ([Ca 2+ ] SR ) can be explained by a variety of dysfunctions of elements that participate in the SR Ca 2+ uptake/release balance (e.g.…”