title: Immunofluorescence staining of thin-filament sections not participating in actomyosin crossbridges: studies by use of a monoclonal antibody specific to actin.
abstract: Monoclonal antibodies (mcab) were produced in vitro by fusing mouse X63-Ag8.653 plasmacytoma cells with spleen cells from a Balb/c mouse immunized with primary cultures of chick skeletal muscle (pmcc). After cloning on agar, stable clones were obtained, the antibodies of which stain specifically the I-band of myofibrils in the immunofluorescence (IF) procedure. For further characterization of these mcab their affinities to muscle proteins were tested by immunoblotting and by enzyme-linked immunosorbent assay (ELISA). Mcab specific for actin were revealed by these criteria. One of the anti-actin antibodies, mcab 647, reveals a variety of IF-staining patterns on myofibrils. On rest-length myofibrils the I-band is labeled only. However, at sarcomere lengths below 2 micrometers, where the thin filaments meet in the middle of the A-band and form a region of double overlap, an additional fluorescent band appears in this position. The fluorescence intensity of this band is increased significantly in shorter sarcomeres. Finally, when the I-band has disappeared at a sarcomere length of 1.5 micrometer, fluorescence is located exclusively in the middle of the A-band. These IF-staining patterns suggest that only those sections of the thin filament are stained that do not participate in actomyosin crossbridges.
mesh_terms: D000199:Actins / Q000276:immunology / Q000502:physiology*; D000205:Actomyosin; D000818:Animals; D000911:Antibodies, Monoclonal; D002642:Chick Embryo; D003599:Cytoskeleton / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D009119:Muscle Contraction; D012518:Sarcomeres / Q000648:ultrastructure
chemical_list: D000199:Actins; D000911:Antibodies, Monoclonal; D000205:Actomyosin