Post‐tetanic and drug‐induced repetitive firing in the soleus muscle of the cat

Abstract

1. The effects of a high frequency indirect tetanus on the responses to subsequent infrequently applied nerve shocks have been compared in the tibialis anterior and soleus muscles of cats and rabbits. 2. Post-tetanic augmentation of twitches in the cat soleus muscle was shown to be partly due to repetitive firing and partly due to increased synchronization of the muscle fibre response. Post-tetanic repetitive firing was not evident in the responses of the other three muscles studied. 3. Post-tetanic repetitive responses in the cat soleus muscle and nerve did not originate in the nerve trunk and were not produced by direct muscle stimulation; they were abolished by doses of tubocurarine smaller than those necessary to reduce the twitch tension below the pre-tetanic level. These findings support the conclusion of others that the repetitive firing originates at the neuromuscular junction. 4. The repetitive firing could not be explained by an increase in the sensitivity of the motor endplates to acetylcholine, suggesting that an increase in and/or a prolongation of the output of transmitter from the motor nerve contributes to it. 5. The cat soleus muscle was shown to be more sensitive to neostigmine than were the other three muscles studied, and acetylcholinesterase determinations showed that this muscle possesses less enzyme activity. 6. It is concluded that an increase in transmitter output, coupled with a weaker cholinesterase activity, probably accounts for the post-tetanic repetitive activity in the cat soleus muscle. 7. Post-tetanic repetitive firing was absent in cat soleus muscles which had been cross-innervated with the nerve formerly innervating a fast-contracting muscle.After a period of high frequency stimulation of the motor nerve innervating the slow-contracting soleus muscle of the cat, augmented contractions associated with repetitive firing of the muscle fibres are temporarily produced in response to each

The Role of Pre- And Post-Junctional Cholinoceptors in the Action of Neostigmine at the Neuromuscular Junction

“…The strength of the stimuli, which were supplied from a Grass (Model S4) stimulator, were at least twice those required to evoke maximal twitches. The method was identical with that described by Bowman et al (1969). The muscle and ventral root action potentials were amplified by Nihon Kohden Bio-physical amplifiers (Model AVB-2) and displayed concurrently on a Nihon Kohden (Model VC-7A) dual beam oscilloscope, from which they were photographed on a 35 mm film.…”

“…In the latter case, the contralateral soleus muscle was attached to a second similar strain gauge coupled to the Servoscribe recorder. In all experiments, muscle temperature was maintained at 36-38°C as previously described (Bowman et al, 1969).…”

“…Therefore, the actions of hexamethonium, tubocurarine, gallamine and pancuronium were compared on neostigmineinduced twitch augmentation, repetitive firing in the muscle, muscle fasciculations, and antidromic repetitive firing in the nerve of the soleus muscle of cats under chloralose anaesthesia. The soleus muscle was chosen because of its prolonged and relatively constant response to neostigmine (Bowman, Goldberg & Raper, 1969).…”

Effects of high-frequency initial pulses and posttetanic potentiation on power output of skeletal muscle

“…It should be noted, however, that PTP is primarily found in fast-twitch muscle. Although some reports have been made concerning PTP in cat soleus (4,22), slow-twitch muscles are predominantly known to cause posttetanic depression (5). Because the effects of PTP in fast-twitch muscle have been reported to last several minutes, most investigations into the mechanisms have concentrated on long-lasting changes due to tetanic stimulation such as an increased phosphorylation rate of the myosin light chains.…”

Abnormal innervation of the cat soleus muscle

“…This preparation has also been used in the investigation of motor nerve terminal responses (Riker, Roberts, Standaert & Fujimori, 1957;Bowman, Goldberg & Raper, 1969;, and recently microelectrode analysis of neuromuscular transmission (Hoekman, Dretchen & Standaert, 1974).…”