Symmetric and asymmetric processes in the mechano-chemical conversion in the cross-bridge mechanism studied by isometric tension transients.
The substrate concentration dependence of isometric tension transients in response to a quick stretch and release of glycerinated muscle fibers was studied during the first few seconds with a time resolution of submilliseconds . Observed tension transients apparently comprise five rate processes, which are named process (1), (1'), (2), (3) and (4) in order of fast to slow. It was found that they might be classified into two groups: one is composed of processes (1), (1') and (4) and the other of processes (2) and (3). The processes belonging to the first group give a symmetric response with respect to the direction of the length change such that not only the rate but also the fraction of the processes are about the same in magnitude for stretch and release. However, this is not the case for the processes belonging to the second group, which give an asymmetric response. In addition, the rate of the processes belonging to the second group depends on substrate concentration while the rate of those belonging to the first group does not when substrate concentration is higher than a few tens of micromolar. The symmetric processes are attributed to mechanical changes in the property of cross-bridge whereas the asymmetric ones to those accompanying chemical changes. The early tension recovery phase is comprised not only of processes (1) and (1') but also of (2) whose rate is proportional to substrate concentration and the square of substrate concentration for stretch and release, respectively.
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D007700:Kinetics; D008838:Microcomputers; D008954:Models, Biological; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000502:physiology*; D011817:Rabbits; D012518:Sarcomeres / Q000502:physiology
D000255:Adenosine Triphosphate