The ryanodine receptor store-sensing gate controls Ca ²⁺ waves and Ca²⁺-triggered arrhythmias

Spontaneous Ca ²⁺ release from intracellular stores is important for various physiological and pathological processes. In cardiac muscle cells, spontaneous store overload-induced Ca 2+ release (SOICR) can result in Ca ²⁺ 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 region (the proposed gate) of the cardiac ryanodine receptor (RyR2) completely abolishes luminal, but not cytosolic, Ca ²⁺ activation of RyR2. The introduction of metal-binding histidines at this site converts RyR2 into a luminal Ni ²⁺-gated channel. Mouse hearts harboring a heterozygous RyR2 mutation at this site (E4872Q) are resistant to SOICR and are completely protected against Ca ²⁺-triggered VTs. These data show that the RyR2 gate directly senses luminal (store) Ca ²⁺, explaining the regulation of RyR2 by luminal Ca ²⁺, the initiation of Ca ²⁺ waves and Ca ²⁺-triggered arrhythmias. This newly identified store-sensing gate structure is conserved in all RyR and inositol 1,4,5-trisphosphate receptor isoforms.