Dynamic Regulation Mechanism of Calcium Ions on Muscle Fiber Contraction During Deformation Process of Honeybee Abdomen

Various physiological activities of the honeybee abdomen depend on muscle contraction, mainly regulated by calcium ions. Thus, the dynamic changes of calcium ions are crucial for unraveling the molecular mechanism of muscle contraction but remain unclear. Considering that calcium ions bind to troponin on thin filaments to induce the formation of actomyosin cross-bridges, fluorescence labeling technology can be employed to investigate the dynamic regulatory effect of calcium ions on muscle fibers. Here we show that the calcium ion concentration first increased and then gradually decayed under the simulation of L-glutamic acid, leading to a gradual decay of the changes in the length of muscle fibers until they were almost unchanged, at which point the maximum contraction was reached. The contraction rate of the muscle fibers was fastest at the beginning and then decreased as the calcium ion concentration decreased. The maximum extent of muscle fiber shortening sizes was about 20 μm, with the initial size of about 225 μm. A model of half sarcomere contraction stimulated by calcium ions was established to further verify the effects of calcium ions on muscle fiber contraction, and the consistent tendency with the experiment demonstrated good agreement on the regulatory effect of calcium ions on muscle fiber contraction. This finding provides a deeper understanding of the dynamic process of muscle contraction in insects and an important reference for the design of integrated soft-body actuators, especially ion-regulated actuators.