Enhancement and diminution of mechanical tension evoked by staircase and by tetanus in rat muscle

Abstract

SUMMARY1. Potentiation of the isometric twitch tension was compared during and after the staircase and after tetanic stimuli in the fast-twitch extensor digitorum longus muscle of adult Lewis rats at 37-380C.2. With up to 250 stimuli the potentiation rose with an increase in both the frequency and number of stimuli in the staircase (2-5/sec) and the tetanus (100-167/sec). After a tetanus of 375 stimuli (125/sec) the potentiation was smaller.The potentiation 2 sec after a tetanus of250 stimuli (167/sec) was + 132 ± 5% (n = 21, S.E. of mean) which was greater (P < 01001) than at the 250th stimulus at 5/sec, +92+3% (n = 21, S.E. of mean).3. After the staircase the decay of potentiation was initially slow and later more rapid. This was taken to indicate both the recovery ofa process that diminished twitch tension and the decay of a process causing potentiation. After 250 stimuli (5/sec) the rate of decay of the processes causing diminution and potentiation had time constants of 34-5+3-8 sec (n = 18, 5.E. of mean) and 102-2+666 sec (n = 20, S.E. of mean) respectively. Compared with the potentiation, the process causing diminution became relatively more pronounced the greater the frequency of stimuli.4. The decay of post-tetanic potentiation showed an initial rapid and a later slower phase of decay. After a tetanus of 250 stimuli (167/sec) the rates of decay had time constants of 5-7+0 8 sec (n = 16, S.E. of mean) and 113-5+±87 sec (n = 19, S.E. of mean) respectively.5. Compared with the unpotentiated response the time course of the twitch was shortened initially in the staircase and when the post-tetanic potentiation was low. The contraction time was then increasingly prolonged the greater the potentiation and the greater the number of stimuli in the staircase and in the tetanus. The half-relaxation time was the more prolonged the greater the number of stimuli.6. Potentiation can be described in terms of a two-compartment model ofprocesses which show saturation. Both compartments were activated in a tetanus whereas only the compartment with a slow rate of decay was activated in the staircase. It is speculated that the two compartments are related to the excitation-contraction Present address:

Staircase in mammalian muscle without light chain phosphorylation

“…It is known that the staircase response is obtained by an increased intensity of activation, not a prolongation of activation (14,20). In the control and sham animals prior to dantrolene treatment, R-LC phosphorylation probably plays an important role in the staircase response.…”

The effect of work cycle frequency on the potentiation of dynamic force in mouse fast twitch skeletal muscle

“…In rodent hindlimb muscles, for example, an increased isometric twitch force is often observed during low frequency contractile activity or following brief, high frequency contractile activity (i.e. staircase and post-tetanic potentiation, respectively) (Close and Hoh, 1968a;Krarup, 1981a). Biochemical studies illustrate that the same cytosolic Ca 2+ signal that activates muscle contraction also generates a signalling cascade that phosphorylates the RLC in a stimulation frequency-and durationdependent manner (Klug et al, 1982;Manning and Stull, 1982;Moore and Stull, 1984).…”

The influence of changes in hand temperature on the indirectly evoked electromyogram of the first dorsal interosseous muscle

“…The gradient between skin and muscle temperature is difficult to predict. Heir et al 9 found that skin temperature averaged 2.2 ~ C below muscle temperature, which in turn was 0.8~ below core temperature. However, it appears that in that investigation the hand under study was exposed to ambient operating room temperatures.…”