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
• ISSN: 0014-4827; 1090-2422
• DOI: 10.1016/S0014-4827(03)00231-3

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.