Modification of the Ca²⁺ Release System of Skeletal Muscle Sarcoplasmic Reticulum Vesicles via Sulfhydryl Oxidation and Tryptic Proteolysis

Abstract

The sarcoplasmic reticulum (SR) is an intracellular membrane system found in muscle cells which regulates the concentration of Ca S + ions in muscle cytoplasm. ATPdependent Ca s + pumps actively transport Ca Z + from the cytoplasm across the membrane, where it is stored within the lumen of the SR. When the cell is in the relaxed state, the cytoplasmic Ca Z + concentration is -10-7 M. In response to excitation of the cell at the neuromuscular junction, the normally polarized membrane of the cell depolarizes.Depolarization of the surface membrane and the associated transverse tubular system signals the SR, via a poorly understood mechanism, to release its stored Ca s +. The released Ca S + activates the contractile elements of the cell.