X-ray Diffraction from a Left Ventricular Wall of Rat Heart

Abstract

We studied x-ray diffraction from the left ventricular wall of an excised, perfused whole heart of a rat using x rays from the third-generation synchrotron radiation facility, SPring-8. With the beam at right angles to the long axis of the left ventricle, well-oriented, strong equatorial reflections were observed from the epicardium surface. The reflections became vertically split arcs when the beam passed through myocardium deeper in the wall, and rings were observed when the beam passed into the inner myocardium of the wall. These diffraction patterns were explained by employing a layered-spiral model of the arrangement of muscle fibers in the heart. In a quiescent heart with an expanded left ventricle, the muscle fibers at the epicardium surface were found to have a (1,0) lattice spacing smaller than in the rest of the wall. The intensity ratio of the (1,0) and (1,1) equatorial reflections decreased on contraction with a similar time course in all parts of the wall. The results show that it is possible to assign the origin of reflections in a diffraction diagram from a whole heart. This study offers a basis for interpretation of x-ray diffraction from a beating heart under physiologically and pathologically different conditions.

Fast Measurement of Sarcomere Length and Cell Orientation in Langendorff-Perfused Hearts Using Remote Focusing Microscopy

“…The absolute value of diastolic SL reported here (2.09±0.168 µm) is consistent with results from other groups (1.96-2.1 µm for histological 42 and x-ray diffraction studies, 43 respectively). However, it is higher than the value we previously obtained in a similar preparation (1.95 µm) 13 using a conventional 2-photon microscope.…”

Impact of osmotic compression on sarcomere structure and myofilament calcium sensitivity of isolated rat myocardium

“…Such a mechanism can explain the abrupt transitions that we observed in myofilament calcium sensitivity, I 1,1 /I 1,0 intensity ratio, and interfilament spacing at low levels of applied osmotic compression. A difficulty with this view, however, is that it conflicts with recent studies (30,39) that measured myofilament lattice spacing and I 1,1 /I 1,0 intensity ratio in whole hearts. Both studies reported a diastolic (relaxed) I 1,1 /I 1,0 intensity ratio of ϳ0.4, equivalent to the compressed patterns we observed in the skinned fibers, but the reported myofilament lattice spacing was very different between the two studies: ϳ42 nm (30) and ϳ37.5 nm (39).…”

Synchrotron Radiation Imaging for Advancing Our Understanding of Cardiovascular Function

“…By exposing a finely collimated SR X-ray beam (dimensions, 0.2×0.2 mm) to the whole heart, it is now possible to record the diffraction peaks in a myocardial region without averaging over multiple heart beats at a time resolution of 15 to 20 ms. [78][79][80] The time resolution is not limited by the available flux but mainly by radiation damage. Studies of a whole heart started with the isolated rat heart.…”

“…Studies of a whole heart started with the isolated rat heart. 80 Use of a whole heart has the advantage that it is more physiological than an isolated muscle, and because the mass is larger the diffraction intensity is higher. This helps to reduce the radiation damage.…”

“…It was found that it is possible to account for the diffraction pattern recorded at different angles and depths in the heart. 80 The easiest recording to interpret is diffraction from the epicardium, where the fibers are running only in one direction. At a deeper depth, the X-ray beam passes through layers with Figure 6.…”