RESUMO
Myotoxic effects related to intracellular Ca(2+) disturbances have been reported for local anesthetics. Such effects might derive from Ca-ATPase dysfunction. The aim of this work was to describe the effect of lidocaine and bupivacaine on the sarcoplasmic reticulum (SR) Ca-ATPase from fast-twitch skeletal muscle and to identify the affected steps of the enzyme's cycle. SR sealed vesicles were isolated from rabbit fast-twitch muscles by ultracentrifugation. The effect of the anesthetics on Ca-ATPase activity was assessed with a colorimetric method and Ca(2+) binding, uptake, phosphorylation of the enzyme by ATP, Ca(2+) dissociation kinetics and phosphoenzyme formation and decomposition levels were tested with radioisotopic methods. Lidocaine and bupivacaine inhibited Ca-ATPase activity with half-maximal inhibitory concentrations (Ki) of 25.3 and 31.4 mM, respectively, and the steady-state Ca(2+) transport ability with Ki values of 33.6 and 46.5 mM, decreasing the maximal transport rate without modification of the Ca(2+) or ATP affinity for the enzyme. This is consistent with an absence of competition for the transport and catalytic sites. The anesthetics did not inhibit Ca(2+) binding but inhibited the phosphorylation partial reactions. Ca(2+) dissociation kinetics was not affected, but the phosphoenzyme levels were decreased, and the decomposition rate of the phosphoenzyme became faster in the presence of the anesthetics. It is concluded that lidocaine and bupivacaine at concentrations available in pharmaceutical formulations for clinical medical and dental uses inhibit the SR Ca-ATPase through inhibition of key phosphorylation steps of the enzymatic cycle.
Assuntos
Anestésicos Locais/farmacologia , Bupivacaína/farmacologia , Lidocaína/farmacologia , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/antagonistas & inibidores , Animais , Masculino , Fibras Musculares de Contração Rápida/enzimologia , Coelhos , ATPases Transportadoras de Cálcio do Retículo Sarcoplasmático/metabolismoRESUMO
The exposure to high doses of ionizing radiation during radiotherapy results in severe morphological and functional alterations of the salivary glands, such as xerostomia. In the present study we investigated the chronic effect of a single radiation dose of 15 Gray (Gy) limited to head and neck on rat salivary gland function (salivary secretion and gland mass) and histology. Results indicate that norepinephrine (NE)-induced salivary secretion was reduced significantly at 30, 90, 180 and 365 days after the administration of a single dose of 15 Gy of ionizing radiation compared to non-irradiated animals. The maximal secretory response was reduced by 33% at 30 and 90 days post irradiation. Interestingly, a new fall in the salivary response to NE was observed at 180 days and was maintained at 365 days post irradiation, showing a 75% reduction in the maximal response. The functional fall of the salivary secretion observed at 180 days post irradiation was not only associated with a reduction of gland mass but also to an alteration of the epithelial architecture exhibiting a changed proportion of ducts and acini, loss of eosinophilic secretor granular material, and glandular vacuolization and fibrosis. On the basis of the presented results, we conclude that ionizing radiation produces irreversible and progressive alterations of submandibular gland (SMG) function and morphology that leads to a severe salivary hypo-function.