This SPRY domain is the first of three structural repeats in all three isoforms of the ryanodine receptor (RyR), which are the major Ca2+ release channels in the membranes of sarcoplasmic reticulum (SR). There are three RyR genes in mammals; the skeletal RyR1, the cardiac RyR2 and the brain RyR3. The three SPRY domains are located in the N-terminal part of the cytoplasmic region of the RyRs. The first domain may be involved in RyR2 dimerization.