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)-dihydr opyridine receptor triggers Ca2+-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, m aintenance, and stabilization of triads. Here, we analyzed the expression p attern and neighborhood relationship of a novel 90-kDa sarcoplasmic reticul um protein. This protein is highly enriched in the triad fraction and is pr edominantly expressed in fast-twitching muscle fibers. Chronic low-frequenc y electro-stimulation induced a drastic decrease in the relative abundance of this protein. Chemical crosslinking showed a potential overlap between t he 90-kDa junctional face membrane protein and the ryanodine receptor Ca2+- release channel, suggesting tight protein-protein interactions between thes e two triad components. Hence, Ca2+-regulatory muscle proteins have a stron g tendency to oligomerize and the triad region of skeletal muscle fibers fo rms supramolecular membrane complexes involved in the regulation of Ca2+-ho meostasis and signal transduction. (C) 1999 Academic Press.