Ryanodine Receptor (RyR)
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The contraction of cardiac and skeletal muscles requires the release of Ca2+ from the sarcoplasmic reticulum (SR) through specialized membrane proteins. The ion channels responsible for the release were not identified until the late 1980s. Ryanodine is an alkaloid found in the South American plant Ryania speciosa, and has insecticidal activity. This compound was found to bind to the elusive Ca2+ release channel, which was subsequently named the Ryanodine Receptor (RyR) (Meissner 1986). Early biochemical evidence first showed that the channel exists as a homotetramer, with each monomer having a mass of ∼550 kDa. This makes RyRs the largest known ion channels at ∼2.2 MDa (Lai et al. 1988). They were shown to be located in the SR with a “foot” region that spans the gap between the transverse tubule and the SR. Work on...