Characteristics of the Sarcoplasmic Reticulum Ca²⁺-dependent ATPase from Masticatory Muscles

Abstract

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.

Expression of sarcoplasmic‐endoplasmic reticulum Ca‐ATPase isoforms in masticatory muscles

“…Our first experiments were devised to isolate highly pure SERCA from elevator and depressor masticatory muscles. As in earlier studies we demonstrated that the procedure of Champeil et al . allows the isolation of sealed SR membranes with highly specific Ca‐ATPase activity from both masticatory and fast‐twitch muscles, and this procedure was used to obtain SR membrane fragments.…”

“…Despite the above‐mentioned similarities, it seems likely that functional differences exist among the SERCA isoforms which, combined with masticatory muscle‐specific expression of fast‐ and slow‐twitch muscle isoforms, might result in lower Ca‐ATPase activity and calcium transport capability. This was recently reported for masseter and medial pterygoid muscles , and accounts for the heterogeneous composition of masticatory muscles. To test this hypothesis we used SERCA‐specific antibodies to assess the distribution of the different isoforms.…”

“…The functional aspects of SERCA, such as structure , enzymatic activity, modulation of calcium transport, binding and efflux, and phosphorylation by ATP and inorganic phosphate (Pi) , as well as the effects of different drugs and cations , have been studied in detail in sarcoplasmic reticulum (SR) membranes isolated from fast‐twitch skeletal muscles. However, few authors have reported on SERCA isolated from masticatory muscles . Similar optimal conditions for SERCA enzymatic activity and calcium transport in masticatory muscles compared with fast‐twitch muscles have recently been reported .…”

“…However, few authors have reported on SERCA isolated from masticatory muscles . Similar optimal conditions for SERCA enzymatic activity and calcium transport in masticatory muscles compared with fast‐twitch muscles have recently been reported . Despite the above‐mentioned similarities, it seems likely that functional differences exist among the SERCA isoforms which, combined with masticatory muscle‐specific expression of fast‐ and slow‐twitch muscle isoforms, might result in lower Ca‐ATPase activity and calcium transport capability.…”

Local Anesthetics Inhibit Ca-ATPase in Masticatory Muscles

“…Few authors have studied the Ca-ATPase from masticatory muscles (Okabe et al, 1985;Sánchez et al, 2004). Studies on the effect of dental drugs on the Ca-ATPase from masseter and medial pterygoid muscles have not yet been published.…”