X-ray structural analysis of single adult cardiomyocytes: tomographic imaging and micro-diffraction

We present a multi-scale imaging approach to characterize the structure of isolated adult murine cardiomyocytes based on a combination of full-field three-dimensional (3d) coherent x-ray imaging and scanning x-ray diffraction. Using these modalities, we probe the structure from the molecular to the cellular scale. Holographic projection images on freeze-dried cells have been recorded using highly coherent and divergent x-ray waveguide radiation. Phase retrieval and tomographic reconstruction then yield the 3d electron density distribution with a voxel size below 50 nm. In the reconstruction volume, myofibrils, sarcomeric organisation and mitochondria can be visualized and quantified within a single cell without sectioning. Next, we use micro-focusing optics by compound refractive lenses to probe the diffraction signal of the acto-myosin lattice. Comparison between recordings of chemically fixed and untreated, living cells indicate that the characteristic lattice distances shrink by approximately 10% upon fixation. SIGNIFICANCEDiffraction with synchrotron radiation has played an important role to decipher the molecular structure underlying force generation in muscle. In this work, the diffraction signal of the actomyosin contractile unit has for the first time been recorded from living cardiomyocytes, bringing muscle diffraction to the scale of single cells. In addition to scanning diffraction, we use coherent optics at the same synchrotron endstation to perform holographic imaging and tomography on a single cardiomyocyte. By this hard x-ray microscopy modality, we extend the length scales covered by scanning diffraction and reconstruct the electron density of an entire freeze-dried cardiomyocyte, visualizing the 3d architecture of myofibrils, sarcomers, and mitochondria with a voxel size below 50 nm.