title: Immunogold ultrastructural localization of calpastatin, the calpain inhibitor, in rabbit skeletal muscle.
abstract: The ultrastructural localization of calpastatin, the endogenous inhibitor of the neutral calcium-dependent proteases (calpains), was investigated in rabbit skeletal muscle fibers using a polyclonal antibody against the 34 kDa form of the inhibitor isolated from rabbit. Quantitative studies by pre- and postembedding immunogold techniques revealed that the distribution pattern of the specific immunoreactivity included: 1) the sarcolemma with the adjacent cytoplasm (about 1 micron wide); 2) the myofibrils; 3) the mitochondria and 4) the nuclei (condensed as well as extended chromatin). Other cell substructures, such as lysosomes and the intermyofibrillar cytoplasm, were substantially devoid of immunoreactivity. Furthermore, in accordance to previous light microscope immunohistochemical experiments, an extracellular (endomysial) localization of specific immunoreactivity was confirmed. These results favour the view, which is also supported by a series of biochemical evidences, that calpastatin in rabbit skeletal muscle is present in cell structures also containing calpains and/or their putative substrates. The above multiple patterns of distribution also suggest that the muscular calpain-calpastatin system in skeletal muscle fibers may play different physiological roles in the various subcellular compartments.
authors.affiliation: Institute of Human Anatomy, Catholic University S. Cuore, Rome, Italy.
authors.forename: S L
authors.initials: SL
authors.lastname: Nori
authors.forename: E
authors.initials: E
authors.lastname: Pompili
authors.forename: E
authors.initials: E
authors.lastname: De Santis
authors.forename: G
authors.initials: G
authors.lastname: De Renzis
authors.forename: A
authors.initials: A
authors.lastname: Bondi
authors.forename: W L
authors.initials: WL
authors.lastname: Collier
authors.forename: F
authors.initials: F
authors.lastname: Ippoliti
authors.forename: L
authors.initials: L
authors.lastname: Fumagalli
mesh_terms: D000818:Animals; D002135:Calcium-Binding Proteins / Q000302:isolation & purification*; D002154:Calpain / Q000037:antagonists & inhibitors*; D002467:Cell Nucleus / Q000737:chemistry / Q000648:ultrastructure; D007150:Immunohistochemistry; D016253:Microscopy, Immunoelectron; D008928:Mitochondria / Q000737:chemistry / Q000648:ultrastructure; D009132:Muscles / Q000737:chemistry* / Q000648:ultrastructure*; D009210:Myofibrils / Q000737:chemistry / Q000648:ultrastructure; D011817:Rabbits; D012508:Sarcolemma / Q000737:chemistry / Q000648:ultrastructure
chemical_list: D002135:Calcium-Binding Proteins; C033668:calpastatin; D002154:Calpain