Expression of syntaxin 4 in rat skeletal muscle and rat skeletal muscle cells in culture.

Syntaxins are a family of membrane proteins believed to participate in docking/fusing of arriving vesicles during membrane sorting and secretion. Of the six mammalian syntaxins known, only brain syntaxin 1A/1B has been biochemically characterized in its endogenous form. Syntaxin 4 mRNA is expressed in selective tissues including rat skeletal muscle, although it has not been studied at the protein level in any cell type. Therefore, we generated an affinity-purified antibody against syntaxin 4 to demonstrate that this 36 kDa protein is expressed in rat skeletal muscle and L6 muscle cells in culture. The content of the syntaxin 4 protein increased by 1.9-fold during differentiation of L6 myoblasts into myotubes. By subcellular fractionation the protein was mainly recovered in plasma membrane-enriched fractions of both red and white skeletal muscles and L6 myotubes. Coupled to the recent detection of vesicle associated membrane protein-2 and cellubrevin in skeletal muscle, syntaxin 4 may play a role in membrane traffic in this tissue.