Inhibitory effect of lidocaine on the sarcoplasmic reticulum Ca2+- dependent ATPase from temporalis muscle

Myotoxic effects of local anesthetics on skeletal muscle fibers involve the inhibition of sarcoplasmic reticulum Ca2+-dependent ATPase activity and Ca2+ transport. Lidocaine is a local anesthetic frequently used to relieve the symptoms of trigeminal neuralgia. The aim of this work was to test the inhibitory and/or stimulatory effect of lidocaine on sarcoplasmic reticulum Ca2+-dependent ATPase isolated from rabbit temporalis muscle. Ca2+-dependent ATPase activity was determined by a colorimetric method. Calcium-binding to the Ca2+- dependent ATPase, Ca2+ transport, and phosphorylation of the enzyme by ATP were determined with radioisotopic techniques. Lidocaine inhibited the Ca2+-dependent ATPase activity in a concentration- dependent manner. The preincubation of the sarcoplasmic reticulum membranes with lidocaine enhanced the Ca2+- dependent ATPase activity in the absence of calcium ionophore. Lidocaine also inhibited both Ca2+ uptake and enzyme phosphorylation by ATP but had no effect on Ca2+-binding to the enzyme. We conclude that the effect of lidocaine on the sarcoplasmic reticulum Ca2+-dependent ATPase from temporalis muscle is due to the drug's direct interaction with the enzyme and the increased permeability of the sarcoplasmic reticulum membrane to Ca.

La toxicidad de los anestesicos locales sobre las fibras musculares esqueleticas involucra a la inhibicion de la actividad de la calcio ATPasa del reticulo sarcoplasmico y a la inhibicion del transporte del calcio. Tales efectos inhibitorios no han sido aun descriptos en el musculo temporal. La lidocaina es un anestesico local habitualmente usado para aliviar los sintomas de la neuralgia del trigemino por medio de la anestesia infiltrativa de la region temporal. El objetivo del trabajo fue demostrar el efecto inhibitorio y/o activador de la lidocaina sobre la calcio ATPasa del reticulo sarcoplasmico del musculo temporal del conejo. La actividad de la calcio ATPasa se determino empleando un metodo colorimetrico. La union del calcio a la enzima, el transporte del calcio y la fosforilacion de la ATPasa por ATP se determinaron mediante el empleo de tecnicas radioisotopicas. La lidocaina inhibio a la actividad de la calcio ATPasa. El efecto inhibitorio incremento en funcion de la concentracion del anestesico. La preincubacion de las membranas del reticulo sarcoplasmico en lidocaina incremento la actividad de la calcio ATPasa en ausencia de un ionoforo de calcio. Tal resultado avala el efecto permeabilizante del anestesico local sobre las membranas del reticulo sarcoplasmico del musculo temporal. La lidocaina inhibio la captacion del calcio y la fosforilacion de la calcio ATPasa por ATP, pero no evidencio efecto sobre la union del calcio a la enzima. Concluimos que el efecto de la lidocaina sobre la calcio ATPasa del reticulo sarcoplasmico del musculo temporal se debe a la accion directa de la droga sobre la enzima y al incremento inducido de la permeabilidad de la membrana del reticulo sarcoplasmico al Ca.

Mechanism of inhibition of Ca2+-transport activity of sarcoplasmic reticulum Ca2+-ATPase by anisodamine.

The mechanism of inhibition of Ca2+-transport activity of rabbit sarcoplasmic reticulum Ca 2+-ATPase (SERCA) by anisodamine (a drug isolated from a medicinal herb Hyoscyamuns niger L) was investigated by using ANS (1-anilino-8-naphthalenesulfonate) fluorescence probe, intrinsic fluorescence quenching and Ca 2+-transport activity assays. The number of ANS binding sites for apo Ca2+-ATPase was determined as 8, using a multiple-identical binding site model. Both anisodamine and Ca2+ at millimolar level enhanced the ANS binding fluorescence intensities. Only anisodamine increased the number of ANS molecules bound by SERCA from 8 to 14. The dissociation constants of ANS to the enzyme without any ligand, with 30 mM anisodamine and with 15 mM Ca 2 were found to be 53.0 microM, 85.0 microM and 50.1 microM, respectively. Both anisodamine and Ca2+ enhanced the ANS binding fluorescenc with apparent dissociation constants of 7.6 mM and 2.3 mM, respectively, at a constant concentration of the enzyme. Binding of anisodamine significantly decreased the binding capacity of Ca2+ with the dissociation constant of 9.5 mM, but binding of Ca2+ had no obvious effect on binding of anisodamine. Intrinsic fluorescence quenching and Ca2+-transport activity assays gave the dissociation constants of anisodamine to SERCA as 9.7 and 5.4 mM, respectively, which were consistent with those obtained from ANS-binding fluorescence changes during titration of SERCA with anisodamine and anisodamine + 15 mM Ca2+, respectively. The results suggest that anisodamine regulates Ca2+-transport activity of the enzyme, by stabilizing the trans-membrane domain in an expanded, inactive conformation, at least at its annular ring region.