Desmin filaments influence myofilament spacing and lateral compliance of slow skeletal muscle fibers

Intermediate. laments composed of desmin interlink Z-disks and sarcolemma in skeletal muscle. Depletion of desmin results in lower active stress of smooth, cardiac, and skeletal muscles. Structural functions of intermediate. laments in fast ( psoas) and slow ( soleus) skeletal muscle were examined using x-ray diffraction on permeabilized muscle from desmin-deficient mice ( Des -/-) and controls (Des+/+). To examine lateral compliance of sarcomeres and cells,. lament distances and fiber width were measured during osmotic compression with dextran. Equatorial spacing (x-ray diffraction) of contractile. laments was wider in soleus Des -/- muscle compared to Des+/+, showing that desmin is important for maintaining lattice structure. Osmotic lattice compression was similar in Des -/- and Des+/+. In width measurements of single fibers and bundles, Des -/- soleus were more compressed by dextran compared to Des+/+, showing that intermediate. laments contribute to whole-cell compliance. For psoas fibers, both. lament distance and cell compliance were similar in Des -/- and Des+/+. We conclude that desmin is important for stabilizing sarcomeres and maintaining cell compliance in slow skeletal muscle. Wider. lament spacing in Des -/- soleus cannot, however, explain the lower active stress, but might influence resistance to stretch, possibly minimizing stretch-induced cell injury.