title: Prolonged relaxation after stimulation of the clasping muscle of male frog, Rana japonica, during the breeding season.
abstract: We investigated the mechanical properties of the flexor carpi radialis muscle (FCR), a forelimb muscle used mainly for amplexus in the breeding season (February to March), of the male Japanese brown frog, Rana japonica. In the present experiment, the changes in force and stiffness of the FCR before, during, and after contraction were measured at 4 degrees C. The total time from the end of stimulation to the end of relaxation was about 30 min. The time course of this prolonged relaxation was fitted by two exponential decay processes. Stiffness decreased during prolonged relaxation, but stayed higher than force, when normalized to peak values. These mechanical properties of the FCR were different from those of the glutaeus magnus muscle (GM) in the hindlimb, used for jumping. When a quick release was applied to the FCR during relaxation, the force recovered gradually after a sudden decrease. The time course of this force recovery was fitted by a single exponential term, and the rate constant decreased as the prolonged relaxation proceeded. The possible involvement of active process(es) in the prolonged relaxation is discussed.
authors.affiliation: Department of Physical Therapy, Faculty of Health care Sciences, Himeji Dokkyo University, Kamiono 7-2-1, Himeji, Hyogo 670-8524, Japan. ishii@himeji-du.ac.jp
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Ishii
authors.forename: Teizo
authors.initials: T
authors.lastname: Tsuchiya
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D005552:Forelimb / Q000502:physiology; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D009126:Muscle Relaxation / Q000187:drug effects / Q000502:physiology*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000502:physiology*; D003473:Neuromuscular Nondepolarizing Agents / Q000494:pharmacology; D011898:Ranidae / Q000502:physiology*; D012726:Sexual Behavior, Animal / Q000502:physiology*; D014403:Tubocurarine / Q000494:pharmacology
chemical_list: D003473:Neuromuscular Nondepolarizing Agents; D014403:Tubocurarine