Sarcomere structures in the rabbit psoas muscle as revealed by fluorescent analogs of phalloidin

The fluorescent analogs of phalloidin (rhodamine- and fluorescein-phalloidin) bind tightly to the skinned fibres of rabbit psoas muscle at essentially the same sites as phalloidin and mainly stain the known regions of actin localization in the sarcomere: the thin filaments and Z bands. On both sides of the Z bands, unstained zones were observed, suggesting the presence of proteins tightly bound to the thin filaments. In myofibrils which are stretched to such an extent that the actin and myosin filaments do not overlap, stained bands could also be seen at the myosin-band border, which suggests the localization of actin at these sites.