In skeletal muscle Z bands, the ends of the thin contractile filaments interdigitate in a tetragonal array of axial filaments held together by periodically cross-connecting Z filaments. Changes in these two sets of filaments are responsible for two distinct structural states observed in cross section, the small-square and basketweave forms. We have examined Z bands and A bands in relaxed, tetanized, stretched, and stretched and tetanized rat soleus muscles by electron microscopy and optical diffraction. In relaxed muscle, the A-band spacing decreases with increasing load and sarcomere length, but the Z lattice remains in the small-square form and the Z spacing changes only slightly. In tetanized muscle at sarcomere lengths up to 2.7 micron, the Z lattice assumes the basketweave form and the Z spacing is increased. The increased Z spacing is not the result of sarcomere shortening. Further, passive tension is not sufficient to cause this change in the Z lattice; active tension is necessary.
Structural states in the Z band of skeletal muscle correlate with states of active and passive tension.
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M A Goldstein, L H Michael, J P Schroeter, R L Sass; Structural states in the Z band of skeletal muscle correlate with states of active and passive tension.. J Gen Physiol 1 July 1988; 92 (1): 113–119. doi: https://doi.org/10.1085/jgp.92.1.113
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