The release of Ca$^2+$ ions from intracellular stores is a key
step in a wide variety of cellular functions. In striated muscle,
the release of Ca$^2+$ from the sarcoplasmic reticulum (SR) leads
to muscle contraction. Ca$^2+$ release occurs through large,
high-conductance Ca$^2+$ release channels, also known as ryanodine
receptors (RyRs) because they bind the plant alkaloid ryanodine with
high affinity and specificity. The RyRs are isolated as 30S protein
complexes comprised of four 560 kDa RyR2 subunits and four 12 kDa
FK506 binding protein (FKBP12) subunits. Multiple endogenous effector
molecules and posttranslational modifications regulate the RyRs.
This review focuses on current research toward understanding the
control of the isolated cardiac Ca$^2+$ release channel/ryanodine
receptor (RyR2) by Ca$^2+$, calmodulin, thiol oxidation/reduction
and nitrosylation, and protein phosphorylation.