Local Anesthetics Inhibit Ca-ATPase in Masticatory Muscles

Local anesthetics have myotoxic effects and inhibit CaATPase activity and Ca transport in skeletal muscles. Such effects have not been fully elucidated in masticatory muscles. We tested the hypothesis that local anesthetics increase myoplasmic calcium in masticatory muscles by inhibiting CaATPase at a concentration similar to that of dental cartridges. The effects of lidocaine and bupivacaine on CaATPase from rabbit masseter and medial pterygoid muscles were tested with radioisotopic and colorimetric methods. Bupivacaine had an action similar to that of lidocaine on CaATPase activity, but less effect on calcium transport. The preexposure of the membranes to the anesthetics enhanced the CaATPase activity in the absence of calcium ionophore, supporting their permeabilizing effect. The results demonstrate that amide-type anesthetics do not inhibit calcium binding, but do reduce calcium transport and enzyme phosphorylation by ATP, and suggest that the myoplasmic calcium increase induced by lidocaine and bupivacaine might promote masticatory muscle contraction and eventual rigidity.