Abstract 164: Heart Failure Disrupts Three-dimensional (3d) Geometrics Of Functional Membrane Micro-domains In Myocytes
Global anatomical changes in cellular membrane systems have been recognized in cardiac hypertrophy and heart failure; however, little is known about their impact on the fine anatomy of functional micro-domains that regulate excitation-contraction coupling or other functions. Using 3D electron microscopic tomography, we have successfully visualized the polymorphic 3D structure of t-tubules (T-Ts), junctional sarcoplasmic reticulum (jSR), and dyads in normal and failing hearts at better than 10 nm resolution, both in human tissues and mouse models. Reconstructed T-Ts were highly branched with varying diameters in normal hearts. Compared to those in wild type mice (see Fig⇓), T-Ts in muscle-LIM protein (MLP) null mice, a model of dilated cardiomyopathy (DCM), were dilated and extensively disorganized. Quantitative geometric analyses found that the size of dyads and volume of jSR were significantly reduced in MLP-nulls. Such abnormalities were confirmed in human DCM compared to normal subjects. Furthermore, volume images from double-axis tilt series identified dyad-like junctions between mitochondrial outer-membrane and jSR or T-Ts, which were confirmed in samples prepared via high-pressure freezing/freeze substitution. Nano-gold immuno-EM analyses confirmed ryanodine receptor (RyR) type 2 as a major cardiac RyR isoform localized near jSR, whereas RyR type 1 was also detectable in mitochondria. Unique aspects of this study are the first visualization of 3D geometric changes of well-defined membrane-bound organelles in failing hearts and novel identification of multiple dyad-like structures attached to mitochondria, which may include RyR type 1.