Analysing the lattice transition of thin filaments in striated muscle

Abstract

Thin filaments, through interaction with thick filaments, form the contractile apparatus of striated muscle. Therefore, the length and arrangement of the thin filaments are of key importance to the function of the muscle. The thin filaments from adjacent sarcomeres are anchored at the Z-disc. In 1968 Pringle predicted that thin filament are organised in the Z-disc in a rhomboid lattice rather than a square lattice. Previous experimental evidence has been insufficient to verify Pringle’s suggestion. In the A-band the thin filaments interdigitate with the thick filaments on a hexagonal lattice, hence from the Z-disc to the A-band, there is a transition of the lattice from square to hexagonal. In this project, I have firstly used Fourier analysis and electron tomography to investigate the thin filament lattice in the Z-disc. I have used electron tomography to determine how the lattice transition occurs between the Z-disc and the A-band. Electron tomography of these samples also allowed me to determine the lengths of thin filaments, showing unequivocally that they are of variable lengths in cardiac muscle.