[Z-line structure of the rabbit psoas muscle studied by negative contrast staining]

The ultrastructure of the Z-disc of the rabbit psoas muscle was elucidated by electron microscopy using negative staining technique. Conclusions summarized from this work are as follow: (a) Z-disc involves two layers of Z-filaments, i.e. connecting filaments, which bind thin filaments of adjacent I-discs in the Z-line region. These layers are spaced about 380 A apart. (b) Z-filaments measure 380 A X 30 A. (c) The angle between the connecting filaments and the thin filaments depends on ionic conditions and varies from 20 degrees to 90 degrees. (d) We conclude that alpha-actinin is a structural component of Z-filaments, since dimensions of Z-filaments and their interaction with thin filaments are similar to those of alpha-actinin.