The interaction of local anesthetics with the ryanodine receptor of the sarcoplasmic reticulum

The effects of various local anesthetics (LAs) on the skeletal muscle ryanodine receptor were tested. The LAs were divided into three categories according to their effects on the binding of ryanodine to the junctional sarcoplasmic reticulum membranes. Ryanodine binding was assayed in the presence of 0.2 m NaCl and 10 μm CaCl₂. Tetracaine and dibucaine inhibit the binding with half-maximal inhibition (CI₅₀) of 0.12 and 0.25 m m, respectively, while inhibition by benzocaine and procaine occurs with CI₅₀ of about 10-fold higher. Lidocaine, its analogue QX-314, and prilocaine, on the other hand, stimulate the binding up to fourfold with half-maximal stimulation occurring with about 2 m m of the drugs. Lidocaine increases both the receptor affinity for ryanodine by about fivefold and the rate of ryanodine association with its binding site by about 10-fold. Tetracaine interacts with the ryanodine receptor in a non-competitive fashion with respect to ryanodine but it competes with lidocaine for its binding site, suggesting the existence of a single site for the inhibitory and stimulatory LA. The LAs also interact with the purified ryanodine receptor and produce effects similar to those with the membrane-bound receptor. Tetracaine and dibucaine inhibit binding of the photoreactive ATP analogue; [α-³²P]benzoyl-benzoyl ATP (BzATP) to the ATP regulatory site of the ryanodine receptor, and high concentrations of ATP decrease the degree of ryanodine binding inhibition by tetracaine, indicating the relationship between the receptor conformations stabilized by ATP and LAs. Based on a structure-activity relationship, a model for the LA site of interaction in the ryanodine receptor is suggested.