title: Evidence for the presence of calsequestrin in two structurally different regions of myocardial sarcoplasmic reticulum.
abstract: Localization of calsequestrin in chicken ventricular muscle cells was determined by indirect immunofluorescence and immuno-Protein A-colloidal gold labeling of cryostat and ultracryotomy sections, respectively. Calsequestrin was localized in the lumen of peripheral junctional sarcoplasmic reticulum, as well as in the lumen of membrane-bound structures present in the central region of the I-band, while being absent from the lumen of the sarcoplasmic reticulum in the A-band region of the cardiac muscle cells. Since chicken ventricular muscle cells lack transverse tubules, the presence of calsequestrin in membrane bound structures in the central region of the I-band suggests that these cells contain nonjunctional regions of sarcoplasmic reticulum that are involved in Ca2+ storage and possibly Ca2+ release. It is likely that the calsequestrin containing structures present throughout the I-band region of the muscle cells correspond to specialized regions of the free sarcoplasmic reticulum in the I-band called corbular sarcoplasmic reticulum. It will be of interest to determine whether Ca2+ storage and possibly Ca2+ release from junctional and nonjunctional regions of the sarcoplasmic reticulum in chicken ventricular muscle cells are regulated by the same or different physiological signals.
mesh_terms: D000818:Animals; D002155:Calsequestrin / Q000032:analysis*; D004285:Dogs; D005455:Fluorescent Antibody Technique; D008854:Microscopy, Electron; D009124:Muscle Proteins / Q000032:analysis*; D009206:Myocardium / Q000166:cytology / Q000648:ultrastructure*; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure*
chemical_list: D002155:Calsequestrin; D009124:Muscle Proteins