Inhibits calcium-activated potassium channels (KCa1.1/KCNMA1), voltage-gated potassium channel Kv1.3/KCNA3, and the calcium release channel/ryanodine receptor (RyR). Binds specifically to type 1 RyR (RyR1) from skeletal muscle. Inhibit both the binding of ryanodine to RyR1, and RyR1's calcium-channel activity. Inhibits carbachol-induced muscle contraction and weakly blocks muscle contraction evoked by potassium. Expressed by the venom gland. Belongs to the CRISP family.