Nemaline myopathy, an integrated study: Selective extraction

Low ionic strength extraction of glycerinated skeletal muscle containing nemaline rods removes Z lines before rods or M lines. Low ionic strength extraction also removes Z lines in nemaline muscle more rapidly than in control muscle. Partial extraction of nemaline rods uncovers a highly ordered filament lattice consisting of a set of longitudinal filaments and another set of filaments that pass obliquely to the longitudinal filaments. Spacing and intercepts of the filaments in this lattice are responsible for the longitudinal and transverse periodicities seen in the intact rod. The structure in the rod lattice between adjacent minor transverse periods appears similar to the structure of native Z lines and permits the interpretation that the nemaline rod is a lateral polymer of Z-line subunits. Polyacrylamide gel electrophoretic analysis of the low ionic strength extracts of nemaline muscle, done both in denaturing (SDS) and nondenaturing solvents, reveals that the extracts contain α-actinin and tropomyosin, but do not contain large quantities of new or unknown proteins. Nemaline rods may owe their resistance to low ionic strength extraction to their highly ordered, crystalline lattice, to their sequence of very stable longitudinal filaments, or to both these features. Large deposits of spherical, 200-Å particles in nemaline muscle were identified as glycogen.