Following drug inhibits release of calcium from sarcoplasmic reticulum -

Ans. is 'a' i.e., Dantrolene Dantrolene* This muscle relaxant is chemically and pharmacologically entirely different from neuromuscular blockers; effect superficially resembles that of centrally acting muscle relaxants.* Neuromuscular transmission or MAP are not affected, but muscle contraction is uncoupled from depolarization of the membrane.* Dantrolene acts on the RyRl (Ryanodine Receptor) calcium channels in the sarcoplasmic reticulum of skeletal muscles and prevents Ca2+ induced Ca2+ release through these channels.* Intracellular release of Ca2+ needed for excitation-contraction coupling is interfered with.* Fast contracting 'twitch* muscles are affected more than slow contracting 'antigravity* muscles.* Since Ca2+ channels in the sarcoplasmic reticulum of cardiac and smooth muscles are of a different subtype (RyR2), these muscles are affected little by dantrolene.