ION CHANNELS IN THE SARCOPLASMIC-RETICULUM OF STRIATED-MUSCLE

This review provides a summary of current concepts about the structure and single-channel properties of ryanodine receptor calcium release c hannels and counter ion channels that facilitate Ca2+ release and reup take by the sarcoplasmic reticulum. Some recent results. obtained with single ryanodine receptor ion channels incorporated into lipid bilaye rs from terminal cisternae vesicles of rabbit skeletal muscle and shee p ventricular myocardium. are described. The ryanodine receptor is the major Ca2+ release channel in skeletal and cardiac muscle and has bee n studied in far greater detail than other sarcoplasmic reticulum ion channel proteins. Several ryanodine receptor genes have been cloned an d sequenced. and isoforms of the protein have been detected in muscle and in endoplasmic reticulum of brain and many other tissues from mamm als, lower vertebrates, nematodes and drosophila. The proteins from ai l species are tetramers of a peptide with a molecular mass of approxim ate to 560 kDa, containing approximate to 5000 amino acids. with a sim ilar maximum single-channel conductance of 500-800 pS for monovalent c ations at 250 mM. Results presented here include. Ca2+ activation and adaptation of activity in skeletal ryanodine receptors with rapid chan ges in [Ca2+] controlled by perfusion. activation by FK506 and regulat ion of cooperative gating of skeletal ryanodine receptor channel activ ity by FK506-binding proteins: activation and block of cardiac ryanodi ne receptors by addition of reactive disulphides and by bilayer voltag e. Effects of phosphorylation. calmodulin, triadin, calsequestrin and interactions with the alpha(1) subunit of the dihydropyridine receptor on ryanodine receptor activity are summarized. Potassium and chloride channels in skeletal muscle sarcoplasmic reticulum, are described.