Masticatory muscles of mouse do not undergo atrophy in space

Abstract

Muscle loading is important for maintaining muscle mass; when load is removed, atrophy is inevitable. However, in clinical situations such as critical care myopathy, masticatory muscles do not lose mass. Thus, their properties may be harnessed to preserve mass. We compared masticatory and appendicular muscles responses to microgravity, using mice aboard the space shuttle Space Transportation System-135. Age-and sex-matched controls remained on the ground. After 13 days of space flight, 1 masseter (MA) and tibialis anterior (TA) were frozen rapidly for biochemical and functional measurements, and the contralateral MA was processed for morphologic measurements. Flight TA muscles exhibited 20 6 3% decreased muscle mass, 2-fold decreased phosphorylated (P)-Akt, and 4-to 12-fold increased atrogene expression. In contrast, MAs had no significant change in mass but a 3-fold increase in P-focal adhesion kinase, 1.5-fold increase in P-Akt, and 50-90% lower atrogene expression compared with limb muscles, which were unaltered in microgravity. Myofibril force measurements revealed that microgravity caused a 3-fold decrease in specific force and maximal shortening velocity in TA muscles. It is surprising that myofibril-specific force from both control and flight MAs were similar to flight TA muscles, yet power was compromised by 40% following flight. Continued loading in microgravity prevents atrophy, but masticatory muscles have a different set point that mimics disuse atrophy in the appendicular

The increase in non-cross-bridge forces after stretch of activated striated muscle is related to titin isoforms

“…The force produced by psoas myofibrils was higher than the force produced by soleus, and both were higher than that produced by ventricle myofibrils. Furthermore, the rates of activation and relaxation observed in myofibrils are similar to those observed in other studies (44,45,56,58,59,64,65) and show that the psoas myofibrils are faster than the soleus and ventricles myofibrils, as expected and reported previously. The rates of activation and relaxation are also characteristic of fast and slow muscle fibers, as reported in many studies in the past (for a review see Ref.…”

“…The isometric response at the corresponding final length and the stretch response in pCa 9.0 were subtracted from the response to the stretch in pCa 4.5, to provide a value for the static tension after the stretch. During isometric contractions developed at the plateau of the force-SL relation, the rate of force development (K act) was calculated by fitting a double-exponential equation (F ϭ {a ϫ [1 Ϫ exp(ϪKact ϫ t) Ϫ exp(Ϫl ϫ t)]ϩb}) to the data, and the rate of relaxation (Krel) was calculated by fitting a single-exponential equation (F ϭ {a ϫ exp-[ϪK rel ϫ (t Ϫ c)] ϩ b}) to the data (44,56). For both equations, F is force; t is time; Kact is the rate constant for force development; l is the second rate constant; Krel is the rate constant for force decrease during relaxation; and a, b, and c are constants.…”

Effects of Parkinson's disease on molar bite force, electromyographic activity and muscle thickness of the masseter, temporal and sternocleidomastoid muscles: A case‐control study

“…In the mandibular rest condition, the temporalis muscles (anterior portion) yielded higher electromyographic activity in relation to the masseter muscles in both study groups, which was consistent with known neuroanatomical patterns of movement . The normalised electromyographic activity of the masticatory and cervical muscles was significantly higher in Parkinson's group than in the control group.…”

“…In the mandibular rest condition, the temporalis muscles (anterior portion) yielded higher electromyographic activity in relation to the masseter muscles in both study groups, which was consistent with known neuroanatomical patterns of movement. 25 The…”

Impact of the Consistency of Food Substances on Health and Related Factors of Residents in Welfare Facilities for Seniors in Japan

“…Regular food requires chewing; therefore, it is expected to control dental diseases by promoting salivary secretions, improving oral hygiene, and maintaining immunity [10,11]. Furthermore, the use of masticatory organs and related muscles is expected to prevent disuse atrophy and maintain or enhance chewing and swallowing functions [20]. Regular foods have been reported to contribute toward the maintenance of good nutrition [21] because the calorie content in regular food per unit volume is higher than that in paste food.…”