Redox Modification of Ryanodine Receptors Contributes to Sarcoplasmic Reticulum Ca ²⁺ Leak in Chronic Heart Failure

Abstract

Abnormal cardiac ryanodine receptor (RyR2) function is recognized as an important factor in the pathogenesis of heart failure (HF). However, the specific molecular causes underlying RyR2 defects in HF remain poorly understood. In the present study, we used a canine model of chronic HF to test the hypothesis that the HF-related alterations in RyR2 function are caused by posttranslational modification by reactive oxygen species generated in the failing heart. Experimental approaches included imaging of cytosolic ([Ca2+]c) and sarcoplasmic reticulum (SR) luminal Ca2+ ([Ca2+]SR) in isolated intact and permeabilized ventricular myocytes and single RyR2 channel recording using the planar lipid bilayer technique. The ratio of reduced to oxidized glutathione, as well as the level of free thiols on RyR2 decreased markedly in failing versus control hearts consistent with increased oxidative stress in HF. RyR2-mediated SR Ca2+ leak was significantly enhanced in permeabilized myocytes, resulting in reduced [Ca2+]SR in HF compared to control cells. Both SR Ca2+ leak and [Ca2+]SR were partially normalized by treating HF myocytes with reducing agents. Conversely, oxidizing agents accelerated SR Ca2+ leak and decreased [Ca2+]SR in cells from normal hearts. Moreover, exposure to antioxidants significantly improved intracellular Ca2+-handling parameters in intact HF myocytes. Single RyR2 channel activity was significantly higher in HF versus control because of increased sensitivity to activation by luminal Ca2+ and was partially normalized by reducing agents through restoring luminal Ca2+ sensitivity oxidation of control RyR2s enhanced their luminal Ca2+ sensitivity, thus reproducing the HF phenotype. These findings suggest that redox modification contributes to abnormal function of RyR2s in HF, presenting a potential therapeutic target for treating HF.

A change of heart: oxidative stress in governing muscle function?

“…In a canine model of HF, oxidation of RyR2 causes diastolic Ca 2+ leakage, an effect that could be partially reversed upon treatment with reducing agents (Terentyev et al 2008). Hyperphosphorylation of RyR2 at serines 2809 (Wehrens et al 2006) and 2815 (Ai et al 2005;Guo et al 2006) has been proposed to be involved in increased SR leakage and increased activity of RyR2.…”

Sarcoplasmic Reticulum Ca-ATPase and Heart Failure 20 Years Later

“…[10][11][12] This may occur as a result of phosphorylation, 10 hyponitrosylation, 13 or oxidation. 14 This increased opening will lead to a diastolic leak of Ca, thereby decreasing the SR Ca content. In addition to decreasing systolic function, the leak may also interfere with relaxation by opposing Ca reuptake into the SR. 15 The relative importance of decreased SERCA activity as opposed to increased NCX and RyR leak may depend on the exact model used.…”

Age‐dependent electrocardiographic changes in Pgc‐1β deficient murine hearts

“…Destabilisation of inner mitochondrial membrane potentials results in approximately 10‐fold increases in reactive oxygen species production,25 in turn affecting maximum Na + 25 and K + current,26 sarcolemmal K ATP channel function, Na + and L‐type Ca 2+ channel inactivation kinetics and late Na + current. They also affect ryanodine receptor function alterations in which affect surface membrane excitability and intracellular Ca 2+ homeostasis 27, 28, 29. Mitochondria are also the main cardiomyocyte ATP source and ATP/ADP depletion increases sarcolemmal ATP‐sensitive K + channel (sarcK ATP ) open probabilities affecting action potential duration (APD), effective refractory period (ERP) and heterogenous current sinks potentially causing current‐load mismatch 30.…”

“…These cellular mechanisms could in turn potentially give rise to potentially pro‐arrhythmic effects on cell‐cell coupling,31 AP conduction25 and AP repolarisation 26. There may also be an appearance of alternans and Ca 2+ mediated triggering phenomena 27. The Pgc‐1 β genetic modification has thus been associated with altered ion channel function and ventricular arrhythmias in Langendorff‐perfused heart preparations 15…”