Distribution of the endoplasmic reticulum and its relationship with the sarcoplasmic reticulum in skeletal myofibers

• Published in: Experimental cell research Vol. 289; no. 1; pp. 47 - 57
• Main Authors: Kaisto, Tuula, Metsikkö, Kalervo
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 10-09-2003
• Subjects: Animals; Cell Compartmentation - physiology; Endoplasmic Reticulum - metabolism; Endoplasmic Reticulum - ultrastructure; Export; Female; Fluorescent Antibody Technique; Golgi Apparatus - metabolism; Golgi Apparatus - ultrastructure; Membrane Glycoproteins - metabolism; Microscopy, Electron; Muscle Fibers, Skeletal - metabolism; Muscle Fibers, Skeletal - ultrastructure; Muscle, Skeletal - metabolism; Muscle, Skeletal - ultrastructure; Protein Folding; Protein Transport - physiology; Proteins - metabolism; Rats; Rats, Sprague-Dawley; Recombinant Fusion Proteins - metabolism; recSFV; Sarcoplasmic reticulum; Sarcoplasmic Reticulum - metabolism; Sarcoplasmic Reticulum - ultrastructure; Skeletal myofiber; Vesicular stomatitis virus; Vesicular Transport Proteins; Viral Envelope Proteins - metabolism; Export; Skeletal myofiber; Sarcoplasmic reticulum; ER; recSFV
• DOI: 10.1016/S0014-4827(03)00231-3
• EISSN: 1090-2422
• ISSN: 0014-4827

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.