The 90-kDa junctional sarcoplasmic reticulum protein forms an integral part of a supramolecular triad complex in skeletal muscle

Although it is well established that voltage-sensing of the alpha(1)-dihydropyridine receptor triggers Ca(2+)-release via the ryanodine receptor during excitation-contraction coupling in skeletal muscle fibers, it remains to be determined which junctional components are responsible for the assembly, maintenance, and stabilization of triads. Here, we analyzed the expression pattern and neighborhood relationship of a novel 90-kDa sarcoplasmic reticulum protein. This protein is highly enriched in the triad fraction and is predominantly expressed in fast-twitching muscle fibers. Chronic low-frequency electro-stimulation induced a drastic decrease in the relative abundance of this protein. Chemical crosslinking showed a potential overlap between the 90-kDa junctional face membrane protein and the ryanodine receptor Ca(2+)-release channel, suggesting tight protein-protein interactions between these two triad components. Hence, Ca(2+)-regulatory muscle proteins have a strong tendency to oligomerize and the triad region of skeletal muscle fibers forms supramolecular membrane complexes involved in the regulation of Ca(2+)-homeostasis and signal transduction.