Myofilament Organization in Stone Heart

To determined possible effects on myofilament organization by the stone heart development, trabecular preparations were isolated from fresh control hearts and from hearts with developed stone heart condition. The muscle strips were mounted horizontally using silk thread in a temperature controlled (37°C) cuvette in MOPS buffered physiological solution (NaCl 118, KCl 5, Na₂HPO₄ 1.2, MgC₂ 1.2, CaCl₂ 1.6, glucose 10 mM, pH 7.4). The solution was gassed with air and exchanged every 5–10 min. The cuvette was equipped with Kapton windows and mounted on a stand in the CoSAXS beamline at the MAX IV synchrotron light facility, Lund, Sweden. The X-ray beam (wavelength 1 Å), had a size at the sample of about 50 × 60 μm. The sample detector distance was set to 3.5 m which gave a good resolution of the equatorial pattern using exposures of 0.5–1 s. The sample was moved between exposures to prevent beam damage. Scattering patterns were recorded using an EIGER 2 × 4 M detector (Dectris AG, Baden-Daettwil, Switzerland) and analyzed using a dedicated software. For each sample, recordings were made at different lengths (L) starting at slack length (L_s) and stretched to 1.0, 1.2, 1.3, and 1.4 L/L_s. At each length, the filament lattice spacing and intensity of the equatorial reflections were determined.