Purification and Reconstitution of the Ryanodine- and Caffeine-Sensitive Ca²⁺ Release Channel Complex from Muscle Sarcoplasmic Reticulum

Abstract

Studies in our laboratory are directed towards obtaining a better understanding of the process of excitation-contraction coupling in muscle, primarily using purified membrane and protein preparations. In excitable tissues, release of Ca²⁺ ions can be triggered by a change in surface membrane potential (Ebashi, 1976), or it can occur via a chain of voltage-independent steps that involve agonist-induced formation of inositol 1,4,5-trisphosphate (IP₃) and its subsequent binding and activation of an intracellular membrane receptor/channel complex, the IP₃ receptor (Van Breemen and Saida, 1989). The voltage-dependent mechanism, commonly referred to as excitation -contraction (E-C) coupling, has been most extensively studied in skeletal and cardiac muscle. In striated muscle, rapid release of Ca²⁺ ions from the intracellular membrane compartment, sarcoplasmic reticulum (SR), is triggered by a surface membrane action potential that is thought to be communicated to the SR at specialized areas where the SR comes in close contact with tubular infoldings of the surface membrane (T-tubule). Spanning the gap between the two membrane systems are protein bridges (Peachey and Armstrong, 1983) which have been variously termed “feet” (Franzini-Armstrong, 1970), “bridges” (Somlyo, 1979), “pillars” (Eisenberg and Eisenberg, 1982), or “spanning” proteins (Caswell and Brandt, 1989), and are now believed to be identical with the ryanodine receptor or SR Ca²⁺ release channel complex (Fleischer and Inui, 1989; Lai and Meissner, 1989).