engleski

Carbonylation Induces Heterogeneity in Cardiac Ryanodine Receptors (RyR2) Function During Diabetes.

Heart failure and arrhythmias occur at rates 3-5 times higher in individuals with diabetes mellitus compared with age-matched, healthy individuals. Studies attribute these defects in part to alterations in function of cardiac ryanodine receptors (RyR2), the principal Ca2+ release channel on the internal sarcoplasmic reticulum (SR). To date, mechanisms underlying RyR2 dysregulation during diabetes remain poorly defined. A rat model of type 1 diabetes, in combination with echocardiography, in vivo and ex vivo hemodynamics, video edge-detection, confocal microscopy, Western blots, mass spectrometry, site-directed mutagenesis, [3H]ryanodine binding, lipid bilayer and transfection assays were used to ascertain if post-translational modifications by reactive carbonyl species (RCS) are a contributing cause. After 8 weeks of diabetes, spontaneous Ca2+ release in ventricular myocytes increased ~5-fold. Evoked Ca2+ release from the SR was also non-uniformed (dyssynchronous). Total RyR2 protein remained unchanged, but its ability to bind the Ca2+-dependent ligand [3H]ryanodine was significantly reduced. Western blots and mass spectrometry revealed RCS adducts on select basic residues. Mutating residues to delineate the physiochemical impact of carbonylation yielded channels with enhanced and reduced cytoplasmic Ca2+-responsiveness. The prototype RCS methylglyoxal (MGO) increased then decreased the open probability (Po) of RyR2. MGO also increased spontaneous Ca2+ release and induced Ca2+ waves in healthy myocytes. Treating diabetic rats with RCS scavengers normalized spontaneous and evoked Ca2+ release from the SR, reduced carbonylation of RyR2, and increased binding of [3H]ryanodine to RyR2. From these data we conclude that posttranslational modification by RCS is a contributing cause for heterogeneity in RyR2 activity seen during experimental diabetes.

heart failure; arrhythmias; cardiac ryanodine receptors; diabetes; carbonylation; methylglyoxal

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