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

Muscle contraction is affected by the rapid release of Ca²⁺ ions through Ca²⁺ - conducting channels localized in an intracellular mem- brane compartment, the sarcoplasmic reticulum (SR). The rabbit skel- etal muscle SR Ca²⁺ release channel has been identified as a high-affinity receptor for the plant alkaloid ryanodine, and purified to apparent homogeneity as a 30s protein complex comprising four identical high- mol-wt polypeptide subunits of relative mol mass (M _r ) ~560,000 (it1 -it4 ). Morphological and immunolocalization studies of the ryanodine receptor complex have indicated that the subunits of the tetramer are arranged in the form of a four-leaf clover (1 ,5 ,6 ), and are identical to the previously described bridging structures (“feet”) (7 ) that span the transverse tubular-SR junctional gap (8 ).