Mechanical and Electrical Responses to Single Shocks in Developing Cat Leg Muscles Following Tetanization

Abstract

NYSTROM, B. Mechanical and electrical responses to single shocks in developing cat leg muscles following tetanization. Acta physiol. scand. 1968. 74. 207-225. The effects of 9 sec tetanizations of varying frequencies on isometric twitch and electrical responses were studied in the gastrocnemius, soleus and extensor carpi radialis longus (ECRL) muscles of kittens of varying ages and adult cats. Nembutal® anaesthesia was used. In newborn kittens, no or only slight post-tetanic twitch potentiation (PTP) was recorded in the gastrocnemius muscle, but a PTP of 80-90 % in the soleus. With time, twitch potentiation increased in the gastrocnemius and decreased in the soleus. In the latter muscle of adult cats, PTP was obtained only after high-frequency tetanization (250-450 c/sec). This PTP proved to be due to repetitive activity, and of different magnitude in Nembutal-and chloralose-anaesthetized animals. Changes in contraction and half relaxation time and in tension rise of the twitches occurred post-tetanically. At all ages, post-tetanic muscle action potentials, whether accompanying potentiated twitches or not, showed no consistent change in size, varying ± 10 % from the pre-tetanic values. In young kittens, post-tetanic potentials were slightly delayed. In the gastrocnemius and ECRL of adult cats, there was a short-lasting increase-as compared to the duration of twitch potentiation-in duration of the electrical response, but no change in latency. It is concluded that, in Nembutal-anaesthetized animals, repetitive firing accounts for PTP in the adult cat soleus muscle. The PTP in the soleus of young kittens and in the gastrocnemius and ECRL of the adult animals is, on the other hand, due either to a change within the contractile mechanism of the muscle fibres, or to a recruitment of muscle fibres.

The postnatal development of the inferior oblique muscle of the cat: II. Effects of repetitive stimulation on isometric tension responses

“…This is often seen in slow but seldom in fast muscles of the cat hindlimb, at least in animals anaesthetized with barbiturates (Standaert 1964, Olson andSwett 1971). Shorter stimulations at lower rates give rise to post-tetanic potentiation (PTP) of the excitationcontraction mechanisms, seen most clearly in the twitch response of fast limb muscle (Brown and Euler 1938, Standaert 1964, Buller and Lewis 1965, Nystrom 1968, Olson and Swett 1971, Hanson 1974.…”

“…These effects were not seen in the newborn animal, but became more and more marked in older muscles and reached their maximum at 6-10 weeks of age. Repetitive firing has been observed only in slow muscle (Standaert 1964, Nystrom 1968, Olson and Swett 1971, Stephens and Stuart 1975. The findings in eye muscles would indicate that slow fibres were more or less fully developed at age 10 weeks, and that later changes in muscle characteristics would be caused by the further development of fast fibres.…”

“…Post-tetanic potentiation (PTP) has not been systematically studied in adult eye muscles or during postnatal development. In hindlimb muscles PTP is known to be more pronounced in slow twitch than in fast twitch muscle at birth; the conditions reverse in adult animals, with clear PTP in the fast muscles and almost none in the slow ones (Standaert 1964, Nystrom 1968. With regard to post-tetanic effects in individual motor units of adult hindlimb muscles, Olson and Swett (1971) reported that slow (S) units and fast, quickly fatiguing (FF) units show very little PTP, but that PTP was prominent in fast, fatigue resistant (FR) units, PTP in motor units during postnatal development has not yet been thoroughly examined.…”

Contractile and Histochemical Properties of the Inferior Oblique Muscle in the Rat and in the Cat

“…In the cat I 0 muscles a moderate increase in the amplitude and a marked increase in the decay time of the twitch was seen after stimulation at high frequencies. PTP appearing after high-frequency tetanization in cat soleus muscles is due to repetitive discharge (Bowman et al 1962;Feng et al 1939;Nystrom 1968;Olson &. Swett 1971;Standaert 1964).…”

The postnatal development of the inferior oblique muscle of the cat: I. Isometric twitch and tetanic properties

“…During the first postnatal weeks a differentiation takes place, and some muscles like the gastrocnemius increase their speed of contraction with age, while others like the soleus remain slow throughout development (Buller et al 1960, Buller and Lewis 1965, Nystrom 1968a, Westerman et al 1973. The differentiation of fast and slow contraction seems to occur in parallel with changes in fibre composition (Nystrom 1968b, Maier and Eldred 1974, Hammarberg 1974.…”