|Budget Amount *help
¥1,600,000 (Direct Cost : ¥1,600,000)
Fiscal Year 1991 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1990 : ¥1,100,000 (Direct Cost : ¥1,100,000)
To mtudy the mechanical and metabolic properties of jaw muscles, we analyzed the Ca^<2+> sensitivity of isometric tension development, the ATPase activity, the maximum shortening velocity, and the tension transients in response to small(1 % of muscle length)step length perturbations in glycerinated masticatory muscles (1) of monkey whose mandibular movement seems to be quite similar to that of human and (2) of bite-opened guinea pig whose mandibular movement was focibly limited. In monkey preparations (reasseter, temporalis, superior and inferior lateral pterygoid), the isometric tension increased in sigmoid fashion with an increase in Ca^<2+> concentration. The pea for half maximum tension was 5.88 in masseter, 5.84 in tempolaris, 5.6 in superior lateral pterygoid and 5.90 in inferior lateral pterygoid. The maximum tension was highest in masseter (about 15 g/mm^2) and lowest in superior lateral pterygoid (about 9 g/mm^2). The time constant of the tension transient, which reflects the rate of cross-bridge cycling, was in the-order of masseter<tempolaris = superior lateral pterygoid<inferior lateral pterygoid., In bite-opened guinea pig preparations (masseter and digastric muscles), the Ca^<2+> sensitivity for tension development was decreased with bite-opening. The maximum tension increased significantly only in the masseter of 1-week-bite-opened guinea'pig, and the maximum shortening velocity was increased only in the 1-week-bite-opened digastric muscle. ATPase activity was always increased with an increase in tension development. However, the tension cost (ATPase activity/tension) was decreased only in the masseter of 1-week- bite-opened guinea pig. These results suggest that after 1-week-biteopening, the masseter produces greater tehsion by consuming ATP more economically, while the digastric decreases Ca^<2+> sensitivity and increases the maximum shortening velocity without changing the tension cost.