The aim of this study was to characterize the sarcoplasmic-endoplasmic reticulum Ca-ATPase (SERCA) isoforms in rabbit masticatory muscles compared with those in fast-twitch muscle. It was hypothesized that combined expression of the SERCA isoforms in fast- and slow-twitch muscles accounts for lower Ca-ATPase activity. SERCA was isolated by differential centrifugation, the isoforms were determined by ELISA, and the activity of each isoform was measured using a colorimetric method. Activity was tested for significance by anova, and the distribution of isoforms was assessed using the chi-square test (P < 0.05) and correlated to SERCA activity using Spearman's rank correlation. SERCA1 was predominant (90.5%) in fast-twitch muscle, whereas a mixture of SERCA isoforms was found in masticatory muscles: 62-78% was SERCA2, 20-37% was SERCA1, and the SERCA3 content was negligible. Depressor muscles showed a significantly higher content (77.8%) of SERCA2, and elevator muscles showed a higher content (35.4%) of SERCA1. Elevator muscles showed higher expression of SERCA2a (58%), and depressor muscles showed higher expression of SERCA2b (20%). The SERCA1 content was mainly SERCA1a and significantly higher for elevator muscles (33%), whereas depressor muscles showed a higher content of SERCA1b (4%). The SERCA1 content of fast-twitch muscle was mainly SERCA1a (88.5%). It is concluded that the mixture of different SERCA isoforms, along with a substantial content of SERCA2b, in masticatory muscles would support lower Ca-ATPase activity and calcium transport.

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.

The effect of the local anesthetic benzocaine on sarcoplasmic reticulum membranes isolated from fast-twitch muscles was tested. The effects on Ca-ATPase activity, calcium binding and uptake, phosphoenzyme accumulation and decomposition were assessed using radioisotopic methods. The calcium binding to the Ca-ATPase was noncompetitively inhibited, and the enzymatic activity decreased in a concentration-dependent manner (IC50 47.1 mM). The inhibition of the activity depended on the presence of the calcium ionophore calcimycin and the membrane protein concentration. The pre-exposure of the membranes to benzocaine enhanced the enzymatic activity in the absence of calcimycin, supporting the benzocaine permeabilizing effect, which was prevented by calcium. Benzocaine also interfered with the calcium transport capability by decreasing the maximal uptake (IC50 40.3 mM) without modification of the calcium affinity for the ATPase. It inhibited the phosphorylation of the enzyme, and at high benzocaine concentration, the dephosphorylation step became rate-limiting as suggested by the biphasic profile of phosphoenzyme accumulation at different benzocaine concentrations. The data reported in this paper revealed a complex pattern of inhibition involving two sites for interaction with low and high benzocaine concentrations. It is concluded that benzocaine not only exerts an indirect action on the membrane permeability to calcium but also affects key steps of the Ca-ATPase enzymatic cycle.

Objetivos: determinar la correlación entre medidas del tercer molar inferior y mandibulares. Materiales y métodos: en este estudio descriptivo fueron analizados los siguientes diámetros y longitudes del tercer molar inferior: longitud ocluso-apical (LOA), longitud ocluso-cérvico-vestibular (LOCV), longitud ocluso-cérvico-lingual (LOCL), diámetro mesio-distal (DMD) y diámetro vestíbulo-lingual (DVL). Por otro lado, las medidas mandibulares obtenidas del análisis por software de radiografías panorámicas digitalizadas (n=26), incluyeron: altura (AlR), ancho (AnR) y longitud (LR) de la rama mandibular, longitud del cuerpo mandibular (LC) y longitud del cóndilo (LCo). Se calculó la Media (M) y Error Estándar de la Media (EEM) de cada variable para su análisis estadístico, y su correlación se evaluó con un test de Pearson (p<0.05). Resultados: Las medidas mandibulares (mm) obtenidas fueron: AlR= 61.4±1.7, AnR= 37.8±1.9, LR= 44.1±1.5, LC= 113.6±2.3, LCo= 22.7±0.6, mientras que las dentarias fueron:  LOA= 17.9±0.3, LOCV= 7.6±0.1, LOCL= 6.6±0.1, DMD= 11.1±0.2 y DVL= 9.9±0.1. Se observaron correlaciones univariadas significativas entre AnR y DVL (r=0.64), AlR y LOA (r= 0.76), LC y DMD (r=0.57). Se observó que tanto las medidas transversales como las longitudinales de la mandíbula y el tercer molar tienden a correlacionarse entre sí.  Conclusiones: la correlación encontrada entre la morfometría del tercer molar y las medidas mandibulares ayudaría a estimar diámetros y longitudes del tercer molar a partir de radiografías panorámicas, siendo de utilidad en la planificación de cirugías de dicho molar.