Characteristics of compensatory hypertrophied muscle in the rat: II. Comparison of histochemical and functional properties

BACKGROUND: We reported that numerous complex branched fibers (CBF) are present in the compensatory hypertrophied plantaris muscle prepared by surgical removal of the synergist muscles in the rat. To investigate the functional effects of these CBF, we examined the histochemical and contractile properties of this muscle. METHODS: Compensatory hypertrophied plantaris (PLA) muscles were prepared by ipsilateral ablation of synergistic muscle in male Wistar rats. We compared the operated (OP), contralateral (CON-L), and nonoperated age-matched normal control (NOR-C) plantaris muscles. Contractile properties under urethane anesthesia and histochemical properties (myofibrillar ATPase staining) were examined at 6, 10, and 15 weeks after surgical preparation of the muscles. RESULTS: The weight of the OP muscle was 48-55% higher than that of the CON-L muscle. The twitch-time-to-peak tension (TPT) and half-relaxation time (HRT) were slower in NOR-C < CON-L < OP. The shift to slower muscle characteristics was also associated with a similar order (NOR-C < CON-L < OP) of histochemical analysis. However, the fatigue resistance capacity of OP (time to 50% fall in tension from initial peak tension during 15-Hz twitch train) was less than that of CON-L, in contrast to the results of twitch, tetanus, and histochemical analysis. The order of NOR-C < CON-L < OP was not observed in the fatigue-resistance test. CONCLUSIONS: Our results suggest that the presence of CBF may disturb the correlation between histochemical and functional properties of the whole muscle. In addition, the CON-L muscle clearly shifted to slower muscle characteristics, indicating that it was not similar to normal control muscle.