Abstract
Flexor carpi radialis muscle (FCR) is one of the forelimb muscles in frog used for mating posture, amplexus. We measured the change in force and stiffness of the muscle before and after amplexus of three weeks in breeding season at 4°C.It was found that the muscle before and after amplexus has characteristic ‘long-lasting relaxation (more than 30 min) after contraction’ and that the relaxation was composed of three phases, which were separated clearly by two changing points (CP) on force curve. The first phase was fast and the second and third phases were slow, the third phase being the slowest. Among these three phases, the heights of force and stiffness in the second relaxation phase were significantly higher after amplexus. Spontaneous contraction which brought about the increase in force and stiffness without stimulation was also observed after amplexus as well as before amplexus. Present results indicate that the force and stiffness level of the relaxation phase after contraction was raised after amplexus especially by increasing the second phase, suggesting that contraction changed so that it would become more suitable for amplexus. The results about cross-bridge cycle in the relaxation will be also reported. [Jpn J Physiol 55 Suppl:S119 (2005)]
