ryanodine receptor modulator ryanodine receptor agonist A ryanodine receptor modulator which activates the receptor. Ryanodine receptors (RyRs) act as selective ion channels, modulating the release of calcium. Activating the receptors causes the release of calcium, so depleting internal calcium and ultimately preventing further muscle contraction. RyR activator RyR agonists Wikipedia:Ryanodine_receptor