The effect of local anesthetics on the hydrolysis of free and membrane-bound phospholipids catalyzed by various phospholipases

1. 1. A number of local anesthetics related to procaine were shown to inhibit the hydrolytic activity of pure pancreatic phospholipase A towards membrane-bound phospholipids in mitochondria as well as in microsomes from rat liver and towards egg-yolk suspensions. With all substrates, the inhibitory activity decreased with increasing Ca2+ concentrations, and with egg yolk as a substrate we found good evidence of a true competitive effect of Ca2+ on the inhibition. 2. 2. Under slightly variable conditions local anesthetics also inhibited phospholipase C from Bacillus cereus as well as endogenous mitochondrial phospholipase A and lipase activities. 3. 3. Endogenous microsomal phospholipase A activity was stimulated rather than inhibited by the presence of nupercaine. 4. 4. The inhibitory activity of a series of local anesthetics closely paralleled the anesthetic potency of the compounds. 5. 5. Nupercaine, the most powerful inhibitor, was able to maintain respiratory control ratios of isolated rat-liver mitochondria at a constant high level for long periods of time. The effect of phospholipase A inhibition by local anesthetics on the stabilization of biological membranes is discussed and its possible involvement in the mechanism of local anesthesia is suggested. 6. 6. The inhibitory effect of the anesthetics on the pancreatic phospholipase A is dependent on their uptake by the substrate particle: Sonicated liposomes prepared from egg-lecithin failed to take up nupercaine as was indicated by its ultraviolet absorbance spectrum, while their phospholipase A-catalyzed hydrolysis was not inhibited by nupercaine. We suggest that local anesthetics, particularly when applied in conjunction with pure phospholipases, may be useful tools for the detection of the phospholipid arrangement in biological membranes