| Research Abstract |
To study the effects of increased occlusal vertical dimension on (1) the actomyosin kinetics and (2) the fiber-phenotypes of masticatory muscles, we analyzed the sliding velocity of actin filaments on myosins (by an in vitro motility assay), the myosin ATPase activity and the contractile protein compositions in masseter muscles obtained from normal (control) and bite-opened (5.7 mm increase in the vertical dimension for 1 week) guinea pigs.
1. Effects of bite-opening on the actomyosin kinetics.
In control myosin preparations, the actin-filament sliding velocity at 25ﾟC was 4.0(]SY.+-。[)0.3mum/s (mean(]SY.+-。[)SD, n=5). In bite-opened myosin preparations (n=5), it was 3.4(]SY.+-。[)0.3mum/s, a significant (rho<0.01) decrease. Myosin ATPase activity was also decreased significantly (rho<0.01) from 1.0(]SY.+-。[)0.1 to 0.7(]SY.+-。[)0.1 mumol Pi/mg/min (mean(]SY.+-。[)SD,n=5) after the bite-opening treatment. These results suggest that the 1-week bite-opening treatment decreases the turnover ra
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te of actin-myosin interaction in the masseter.
2. Effects of bite-opening on the fiber-phenotypes.
Compositions of myosin heavy chain (MHC), myosin light chain (MLC) and tropomyosin were investigated by gel electrophoresis in conjunction with densitometric analysis. Masseter muscle contained two fast-type MHC isoforms, MHC IIa and IId (or IIx). Averaged densitometric data (n=4) indicated no significant (rho>0.05) change in MHC composition between the two groups. Although the MLC consisted of three components, LC1f, LC2f and LC3f, a significant (rho<0.01) increase in the relative content of LC1f at the expense of that of LC3f was observed after the bite-opening treatment. Although the tropomyosin consisted of two components, TM-alpha and TM-beta, a significant (rho<0.05) increase in the relative content of TM-beta as well as a significant (rho<0.05) decrease in that of TM-alpha were observed in association with the bite-opening treatment.
These results suggest that in guinea pigs the 1-week bite-opening treatment changes the actomyosin kinetics as well as the compositions of MLC and tropomyosin to meet altered functional demands. Less
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