CPM Seminar

The force-length relationship and the cellular mechanisms of muscle contraction

Dilson Rassier

Department of Kinesiology and Physical Education
McGill University

Muscle contraction is typically associated with the cross-bridge theory (Huxley, Prog. Biophys. Biophys. Chem. 7, 255-318, 1957), which predicts that force is produced when the molecular motor myosin binds to actin filaments. We have used new technologies to test crucial predictions of the theory at different levels of analyses (cells, filaments, molecules). In this presentation I will concentrate in studies investigating one of the main pillars of the theory - the relationship between muscle length (and consequently the overlap between myosin and actin) and force. We observed that force cannot always be predicted by the degree of myosin-actin interactions, inconsistent with the cross-bridge theory. We developed new hypotheses that are currently being tested to explain the contrasting results, including the effects of strain on the kinetics of myosin and the engagement of passive structures. If these hypotheses are confirmed, additional mechanisms should be taken into account when investigators model and predict force production during muscle contraction.