Functional types of single muscle fibers from the depressor mandibulae muscle of R. japonica and their mechanism of excitation-contraction (E-C) coupling. I. Isolation, properties and electron microscopy of a single muscle fiber from the depressor mandibu

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The purpose of the present study was to examine the peculiarities of masticatory muscle contraction at the level of the muscle cell. Single muscle fibers were isolated from the depressor mandibulae muscle, which opens the mouth, of R. japonica. Using single muscle fibers, the excitation-contraction (E-C) coupling of this muscle was examined. The present report describes the method of isolating a single muscle fiber and the properties of these fibers. The results of electron microscopy are compared to similar studies of the masseter muscle.<BR>The length of the fibers in the depressor mandibulae muscle was 2.3±0.4 (mean±SD) mm and their diameter was 46.4±11.0μm (N=207). Their resting potential was-86.8±4.7 mV (N=148) and their maximum tension was.212±95 mg (N=138).<BR>Electron microscopy indicated that the depressor mandibulae muscle consists of fast fibers. The contralateral masseter muscle was found to consist of fast, slow and intermediate fibers. These results suggest that the depressor mandibulae muscle contains only fast fibers to rapidly open the mouth; the masseter muscle requires fast, slow and intermediate fibers to rapidly close the mouth, hold, and chew the prey.
歯科基礎医学会の論文