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 catego ries according to their effects on the binding of ryanodine to the jun ctional sarcoplasmic reticulum membranes. Ryanodine binding was assaye d in the presence of 0.2 m NaCl and 10 mum CaCl2. Tetracaine and dibuc aine inhibit the binding with half-maximal inhibition (CI50) of 0.12 a nd 0.25 mm, respectively, while inhibition by benzocaine and procaine occurs with CI50 of about 10-fold higher. Lidocaine, its analogue QX-3 14, and prilocaine, on the other hand, stimulate the binding up to fou rfold with half-maximal stimulation occurring with about 2 mm of the d rugs. 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 recepto r in a noncompetitive fashion with respect to ryanodine but it compete s with lidocaine for its binding site, suggesting the existence of a s ingle site for the inhibitory and stimulatory LA. The LAs also interac t with the purified ryanodine receptor and produce effects similar to those with the membrane-bound receptor. Tetracaine and dibucaine inhib it binding of the photoreactive ATP analogue; [alpha-P-32]benzoyl-benz oyl ATP (BzATP) to the ATP regulatory site of the ryanodine receptor, and high concentrations of ATP decrease the degree of ryanodine bindin g inhibition by tetracaine, indicating the relationship between the re ceptor conformations stabilized by ATP and LAs. Based on a structure-a ctivity relationship, a model for the LA site of interaction in the ry anodine receptor is suggested.