Phosphorylation of RyR₂ and shortening of RyR₂ cluster spacing in spontaneously hypertensive rat with heart failure

As a critical step toward understanding the role of abnormal intracellular Ca²⁺ release via the ryanodine receptor (RyR₂) during the development of hypertension-induced cardiac hypertrophy and heart failure, this study examines two questions: 1) At what stage, if ever, in the development of hypertrophy and heart failure is RyR₂ hyperphosphorylated at Ser ²⁸⁰⁸? 2) Does the spatial distribution of RyR₂ clusters change in failing hearts? Using a newly developed semiquantitative immunohistochemistry method and Western blotting, we measured phosphorylation of RyR₂ at Ser²⁸⁰⁸ in the spontaneously hypertensive rat (SHR) at four distinct disease stages. A major finding is that hyperphosphorylation of RyR₂ at Ser²⁸⁰⁸ occurred only at late-stage heart failure in SHR, but not in age-matched controls. Furthermore, the spacing between RyR₂ clusters was shortened in failing hearts, as predicted by quantitative model simulation to increase spontaneous Ca ²⁺ wave generation and arrhythmias.