Sarcomere, troponin, and myosin X-ray diffraction signals can be resolved in single cardiomyocytes

Area of Science:

• Biophysics
• Cell Biology
• Structural Biology

Background:

• Cardiac function depends on molecular contraction mechanisms within ventricular wall cardiomyocytes.
• Ordered motor proteins generate macroscopic force, typically studied in model tissues via X-ray diffraction.
• Ventricular wall muscle's branched structure and disorder pose challenges for traditional diffraction methods.

Purpose of the Study:

• To demonstrate X-ray diffraction's capability in resolving actomyosin structural organization within single, isolated ventricular cardiomyocytes.
• To identify key structural repeats and determine sarcomere length in these cells.

Main Methods:

• Utilized collimated synchrotron X-ray beams for high-resolution diffraction analysis.
• Applied diffraction techniques to hydrated and fixated single isolated cardiomyocytes.
• Employed Fourier synthesis based on multiple diffraction orders to compute sarcomere density profiles.

Main Results:

• Successfully resolved the hexagonal arrangement of thick and thin filaments.
• Identified diffraction signals corresponding to the myosin motor repeat (M3) and troponin complex repeat (Tn).
• Determined sarcomere length, with signals extending to 13 diffraction orders, consistent with other muscle types.

Conclusions:

• X-ray diffraction can now elucidate the structural organization of actomyosin in individual cardiac cells.
• The findings provide detailed insights into the molecular components and organization of the cardiac sarcomere.
• This methodology paves the way for studying the structural dynamics of living cardiomyocytes during contraction.