The endoplasmic reticulum-sarcoplasmic reticulum connection: Distribution of endoplasmic reticulum markers in the sarcoplasmic reticulum of skeletal muscle fibers

Pompeo Volpe, Antonello Villa, Paola Podini, Adelina Martini, Alessandra Nori, Maria Carla Panzeri, Jacopo Meldolesi

Research output: Contribution to journalArticle


The skeletal muscle sarcoplasmic reticulum (SR) was investigated for the presence of well-known endoplasmic reticulum (ER) markers: the lumenal protein BiP and a group of membrane proteins recognized by an antibody raised against ER membrane vesicles. Western blots of SR fractions revealed the presence of BiP in fast- and slow-twitch muscles of the rabbit as well as in rat and chicken muscles. Analyses of purified SR subfractions, together with cryosection immunofiuorescence and immunogold labeling, revealed BiP evenly distributed within the longitudinal SR and the terminal cisternae. Within the terminal cisternae BiP appeared not to be mixed with calsequestrin but to be distributed around the aggregates of the latter Ca2+ binding protein. Of the various membrane markers only calnexin (91 kDa) was found to be distributed within both SR subfractions, whereas the other markers (apparent molecular masses of 64 kDa and 58 kDa and a doublet around 28 kDa) were concentrated in the terminal cisternae. These results suggest that the SR is a specialized ER subcompartment in which general markers, such as the ones we have investigated, coexist with the major SR proteins specifically responsible for Ca2+ uptake, storage, and release. The differential distribution of the ER markers reveals new aspects of the SR molecular structure that might be of importance for the functioning of the endomembrane system.

Original languageEnglish
Pages (from-to)6142-6146
Number of pages5
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number13
Publication statusPublished - Jul 1 1992


ASJC Scopus subject areas

  • Genetics
  • General

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