Ca2+-ATPase is a major intrinsic protein in the sarcoplasmic reticulum (SR) from skeletal muscles. It actively transports Ca2+ from the cytoplasm to the SR lumen, reducing cytoplasmic [Ca2+] to promote muscle relaxation. Carticaine is a local anesthetic widely used in operative dentistry. We previously showed that carticaine inhibits SR Ca2+-ATPase activity and the coupled Ca(2+) uptake by isolated SR vesicles, and increases the rate of Ca2+ efflux from preloaded vesicles. We also found that these effects were antagonized by divalent cations, and concluded that they were mainly due to the direct interaction of carticaine with the Ca2+-ATPase protein. Here we present additional results on the modulation of the above effects of carticaine by Ca2+ and Mg2+. The activating effect of Ca2+ on the ATPase activity is competitively inhibited by carticaine, indicating a decreased Ca2+ binding to the high affinity Ca2+ transport sites. The activating effect of Mg2+ on the phosphorylation of Ca2+-ATPase by orthophosphate is also inhibited by carticaine. The anesthetic does not affect the reaction mechanism of the cations acting as cofactors of ATP in the catalytic site. On the basis of the present and our previous results, we propose a model that describes the effect of carticaine on the Ca2+-ATPase cycle.

We compared the sarcoplasmic reticulum (SR) Ca-ATPase from masseter (M) and medial pterygoid (MP) muscles with that from fast muscles (FM) to examine whether its calcium transport capability and enzymatic activity are different. SR vesicles from FM, M, and MP muscles were obtained according to Champeil et al.(1985). Assays for characterization of the enzyme properties were performed. The results showed similar optimal conditions for the Ca-ATPase activity and calcium transport in M, MP, and FM. However, the maximal values of calcium transport, Ca-ATPase activity, and K(i) for thapsigargin were significantly lower in the masticatory muscles. These findings are likely related to different Ca-ATPase isoforms. Since the local anesthetics used in dentistry inhibit Ca-ATPase and calcium transport in FM, it will be important for the effects of these drugs on the Ca-ATPase of masticatory muscles to be assessed.