Abstract
To examine the change in mechanical properties and ATPase activity of guinea pig masticatory muscles associated with bite opening, isometric tension, Ca2+-sensitivity, maximum shortening velocity and ATP consumption were measured using glycerinated muscles (3.0-4.5mm in length, 100-200 μn in diameter) obtained from control and bite-opened guinea pigs (3 days, 1 week). Ca2+-sensitivity of the contractile system for tension development was decreased with bite-opening both in the masseter and the digastric. However, the maximum tension increased significantly only in the masseter of the 1-week-bite-opened guinea pigs, and the shortening velocity was increased significantly only in the 1-week-bite-opend digastric muscle. ATPase activity was always increased with an increase in tension development. However, the tension cost (ATPase activity/tension) was significantly decreased only in the masseter of animals receiving 1-week of bite opening. These results suggest that biteopening changes the mechanical property and tension cost of the masseter and the digastric differently. Greater tension was produced in the masseter by consuming ATP more economically after 1-week of bite-opening. Also the digastric decreased Ca2+-sensitivity and increased the shortening velocity, but the amount of ATP consumption was not changed after 1-week of bite-opening.
