Muscle function in animal movement: passive mechanical properties of leech muscle.
We investigated passive properties of leech body wall as part of a larger project to understand better mechanisms that control locomotion and to establish mathematical models that predict such dynamical behavior. In tests of length-tension relationships in 2-segment-long preparations of body wall through step-stretch manipulations (step size = 1 mm), we discovered that these relationships are nonlinear, with significant hysteresis, even for the relatively small changes in length that occur during swimming. We developed a mathematical model comprising three nonlinear springs, two in series with nonlinear dashpots that describe well the tension statics and dynamics for step-stretch experiments. This model suggested that body wall dynamics are slow enough to be neglected when predicting the tension generated by imposed sinusoidal length changes (about +/-10% of nominal) at 1-3 Hz, mimicking swimming. We derived a static model, comprising one nonlinear spring, which predicts sinusoidal data accurately, even when preparations were exposed to serotonin (0.1-10 microM). Preparations bathed in saline-serotonin had significantly reduced steady-state and peak tensions, without alterations in tension dynamics. Anesthetizing preparations (8% ethanol) reduced body wall tension by 77%, indicating that passive tension in the obliquely striated longitudinal muscles of leeches results primarily from a resting tonus.
Tian
Jianghong
J
Department of Biology, University of Virginia, Charlottesville, VA 22904-4328, USA.
Iwasaki
Tetsuya
T
Friesen
W Otto
WO
D000704:Analysis of Variance; D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D017952:Ganglia, Invertebrate / Q000166:cytology; D007865:Leeches / Q000502:physiology*; D008959:Models, Neurological; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D009068:Movement / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D009132:Muscles / Q000502:physiology*; D009142:Musculoskeletal Physiological Phenomena; D010812:Physical Stimulation; D012701:Serotonin / Q000494:pharmacology
D012701:Serotonin