Latency Relaxation and a Theory of Muscular Mechano‐chemical Coupling

Abstract

The purpose of this paper, broadly speaking, is two-fold. First, there will be discussed certain aspects of the latency relaxation (LR), the minute pre-contractile elongation of a stimulated muscle that occurs in the latter half of the latent period, a phenomenon first observed by Rauh (1922). Evidence will be presented to show that the latency relaxation is a real lengthening of the muscle's contractile material that intervenes between the instant of stimulation and the usual shortening or tension development in a contraction. Further, certain studies of the LR will be considered that suggest it is an indication of a process by which myosin is activated for contraction. The second part of this paper will be concerned with a kinetic theory of mechano-chemical coupling which, in part, is based on the particular significance assigned to the LR.The LR was discovered by Rauh in the course of some experiments designed to settle the then almost 70-year-old question as to whether the latent period exists at all. To forestall criticism that the demonstration of a mechanical latency merely represented an inertial delay in the response of the registering device, Rauh used an extremely sensitive mechano-optical isometric lever system and photographically recorded the mechanical change during only the first few milliseconds of the twitch response of initially tensed frog sartorii and gastrocnemii. To his astonishment, his records not only exhibited a true delay in the onset of tension development, but they also included a transient negative tension change (the LR) during the latter half of the latent period. METHODModern electronic methods permit us to achieve vast improvement over Rauh's method. In the work to be reported here, use is made of the piezo-electric cathode-ray oscillographic technique described fully elsewhere (Sandow, 1944). An outline of the method will be given here. A muscle, generally the frog sartorius, is supported inside a moist chamber and, under a few grams resting tension, is connected to the stylus of the piezo-electric pickup, which is a common type of (895)

The time course of early changes in the rate of tension development in electrically‐stimulated frog toe muscle: effects of muscle length, temperature and twitch‐potentiators

“…The duration of the latent period in our experiments agrees well with that reported by Sandow (1947Sandow ( , 1954 for frog sartorius at room temperature, using the same method which we have employed, but is somewhat longer than that described more recently by Sandow & Preiser (1964), using another method and slightly higher temperature. The similarity in the duration of the latent period and the initial step-wise increment in the rate of increase of tension (stage II) as well as the frequent appearance of a third distinct phase of tension acceleration (stage III) of approximately the same duration, suggests that this sequence of stages in the dP/dt curves may arise from some degree of synchronization in the cyclic process of activity which is believed to take place at the individual cross-links between the primary and secondary myofilaments (A. F. Huxley & Niedergerke, 1954;Hanson & H. E. Huxley, 1955; H. E. Huxley, 1960).…”

A large birefringence signal preceding contraction in single twitch fibres of the frog.

“…Latency relaxation and the early optical signal As has been well described (Rauh, 1922;Sandow, 1944Sandow, , 1966Abbott & Ritchie, 1951), the earliest mechanical response detectable during a muscle twitch is actually a slight drop in tension (fibre lengthening) before active shortening. At 200 C this early mechanical response, called 'latency relaxation', begins about 2 ms after stimulation (Sandow, 1944(Sandow, , 1966Mulieri, 1972).…”

“…At 200 C this early mechanical response, called 'latency relaxation', begins about 2 ms after stimulation (Sandow, 1944(Sandow, , 1966Mulieri, 1972). Although latency relaxation is usually measured as a mechanical change at the fibre end, with the longitudinal stimulation used in these experiments its underlying basis probably involves a local sarcomere change propagating along the fibre length with the speed of the action potential (Sandow, 1966). On this view the local change should cumulate as the action potential involves more and more sarcomeres, with a mechanical response becoming apparent on the transducer when the combined lengthening exceeds the base-line noise.…”

Activation delays in frog twitch muscle fibres.

“…CLOSE In earlier work the inflexion in the descending phase of latency relaxation, i.e. the moment of maximum rate of tension decrease, was taken as the end of the twitch latent period and time for onset of positive tension (Sandow, 1944(Sandow, , 1966; that inflexion is at 5-5 msec in the 2-8 gm record in Fig. 2, about 1-5 msec after the onset of the reactivation response at the same length.…”