Effect of an increase in occlusal vertical dimension on the rate of cyclic actin-myosin interaction in guinea-pig masseter muscle

To study the effects of increased occlusal vertical dimension on these kinetics, the actin-filament sliding velocity on masseter myosins in an in vitro motility assay and the ATPase activity of masseter myosins from normal (control [and bite-opened (5.6 mm increase in the vertical dimension for 1 week (guinea.-pigs were measured. In control myosin preparations, the average value (mean ± SD, n = 5) for the actin-filament sliding velocity at 25°C was 4.0 ± 0.3 μm/sec. In bite-opened myosin preparations (n = 5), it was 3.4 ± 0.3 μm/sec a significant (p < 0.01) decrease. Myosin ATPase activity was also decreased significantly (p < 0.01) from 1.0 ± 0.1 to 0.7 ± 0.1 μmol Pi mg per min (mean ± SD, n = 5) after the bite opening. These results strongly suggest that in guinea-pigs an increase in occlusal vertical dimension for 1 week decreases the turnover rate of actin-myosin interaction in the masseter through charges in the myosin isozyme. These changes may result in a slowing of the rate of detachment of myosin cross-bridges from actin filaments.