Sternomastoid muscle fiber types in C57BL/10 mice.

STERNOMASTOID MUSCLE FIBER TYPES IN C57BL/10 MICE. Elaine Minatel, Anderson Neri Guido, Maria Julia Marques, Humberto Santo Neto, Gerson Eduardo Rocha Campos. Department of Anatomy, Institute of Biology, State University of Campinas (Unicamp), Campinas, SP, Brazil.

Skeletal muscle fibers express different isoforms of myosin heavy chain, such as types I, IIa, IId and IIb myosins. Hybrid fibers express more than one isoform. The differences in the pattern of MHC expression among different muscles allow the muscle fibers to adapt to the functional changes that they are subject to over time. At the present, we investigate the fiber typing of the sternomastoid muscle (STN) in C57BL/10 adult (2 months old) mice (n=6). The mice were anesthetized and the STN muscle was removed and oriented in tragacanth gum and immediately frozen in isopentane cooled to -159[degrees]C in liquid nitrogen. The midpoint of the muscle was cut into 12 [micro]m thick sections and the main fiber types and subtypes were delineated by the mATPase technique after preincubation at pH 4.25, 4.55 and 10.6. The sections preincubated at pH 4.55 were mounted photographically and, in combination with those preincubated at pH 4.25 and 10.6, were examined to determine the number and percentage of each fiber type. The STN muscle contained predominantly type II fibers while type I fibers were less abundant. Some IC,IIC, IIAD, IIDB and IIBD hybrid fibers were also present. We conclude that the the STN muscle of C57BL/10 mice is a fast muscle.

Support: FAEP 027/06

Key words: Muscle fiber types; Sternomastoid muscle; C57BL/10 mice