Structural states in the Z band of skeletal muscle correlate with states of active and passive tension.
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.
Goldstein
M A
MA
Department of Medicine, Baylor College of Medicine, Houston, Texas 77030.
Michael
L H
LH
Schroeter
J P
JP
Sass
R L
RL
D000818:Animals; D008854:Microscopy, Electron; D009119:Muscle Contraction; D009132:Muscles / Q000502:physiology / Q000648:ultrastructure*; D051381:Rats; D012518:Sarcomeres / Q000648:ultrastructure