title: Distribution of the endoplasmic reticulum and its relationship with the sarcoplasmic reticulum in skeletal myofibers.
abstract: We have analyzed the distribution of the endoplasmic reticulum (ER) within isolated rat skeletal muscle flexor digitorum brevis myofibers. Studies with confocal microscopy indicated that the resident ER proteins displayed a perinuclear and cross-striated distribution that extended over the I band areas. Interestingly, two discrete distribution patterns were observed when different receptor or viral marker proteins were blocked in the ER. Accordingly, the vesicular stomatitis virus G protein that lost its efficient export through the Golgi apparatus during myogenesis preferentially marked the A-I junctional areas. The proteins that retained their Golgi processing after myogenesis, on the contrary, concentrated around the myonuclei and over the Z lines. Furthermore, the ER exit site marker sec23 located to Z lines but not to A-I junctions. To analyze the ultrastructural organization of the ER, we infected myofibers with recombinant virus expressing KDEL-tagged peroxidase that is translocated into the ER. With transmission electron microscopy, peroxidase activity was found in perinuclear and Z line-flanking tubular structures, but also within the terminal cisternae of the sarcoplasmic reticulum. The translocon-associated protein exhibited a similar localization. Taken together, the terminal cisternae contained unevenly distributed rough ER structures apparently lacking the export function. The exporting ER comprised perinuclear and Z line-flanking structures.
authors.affiliation: Department of Anatomy and Cell Biology, University of Oulu, P.O. Box 5000, Fin-90014 University of Oulu, Finland.
authors.forename: Tuula
authors.initials: T
authors.lastname: Kaisto
authors.forename: Kalervo
authors.initials: K
authors.lastname: Metsikkö
mesh_terms: D000818:Animals; D002451:Cell Compartmentation / Q000502:physiology; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure*; D005260:Female; D005455:Fluorescent Antibody Technique; D006056:Golgi Apparatus / Q000378:metabolism / Q000648:ultrastructure; D008562:Membrane Glycoproteins / Q000378:metabolism; D008854:Microscopy, Electron; D018485:Muscle Fibers, Skeletal / Q000378:metabolism / Q000648:ultrastructure*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000648:ultrastructure*; D017510:Protein Folding; D021381:Protein Transport / Q000502:physiology*; D011506:Proteins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure*; D033921:Vesicular Transport Proteins; D014759:Viral Envelope Proteins / Q000378:metabolism
chemical_list: C028391:G protein, vesicular stomatitis virus; D008562:Membrane Glycoproteins; D011506:Proteins; D011993:Recombinant Fusion Proteins; C512740:Sec23a protein, rat; D033921:Vesicular Transport Proteins; D014759:Viral Envelope Proteins