Ryanodine is a cell permeant ryanodine receptor modulator. Ryanodine can either stimulate or inhibit Ryanodine-mediated Ca²⁺ release depending on its concentrations. Poisonous diterpenoid found in Ryania speciosa. IC50 & Target: Ryanodine receptor^[1] In Vivo: Ryanodine (100-5000 nM, 30-120 mintutes) irreversibly depresses twitch and tetanic tension of both fast and slow muscle in a dose-related manner^[1].

At concentrations above 250 nM, ryanodine induces a slowly developing, dose dependent contracture which could not be blocked by 5 mMCo^2+[1].