Contractile and fatigue properties of thyrotoxic rat skeletal muscle

Abstract

The effects of thyrotoxicosis on the contractile properties and development of muscle fatigue in the slow soleus (SOL) and fast extensor digitorum longus (EDL) muscles were examined in rats given 3 mg of L-thyroxine and 1 mg of L-triiodothyronine per kilogram of diet for 6 weeks. The hormone treatment produced significant decreases in the contraction time, one-half relaxation time, and twitch tension in the SOL, while the peak rate of tension development (+ dP/dt) and decline (- dP/dt) in this muscle were elevated. Additionally, the force-frequency curve was shifted to the right and, thus, resembled the curve of a normal fast-twitch muscle. In contrast, the contractile properties of the fast EDL were relatively unaltered by the hormone administration. Thyrotoxicosis also changed the SOL response to contractile activity as twitch tension, + dP/dt, and - dP/dt remained high, and a faster decline in muscle glycogen and an increase in lactate occurred compared to control muscles. These results clearly demonstrate a preferential effect of thyroid hormone on slow compared to fast skeletal muscle.

Differential effects of thyroid hormone on T-tubules and terminal cisternae in rat muscles: An electrophysiological and morphometric analysis

“…It seems likely that the increase in isometric contraction speed after thryoid treatment is due to changes in excitation-contraction coupling and calcium release, rather than to changes in the properties of the contractile proteins. There is a significant reduction in the rime to peak tension in EDL and soleus fibres after two weeks treatment with thyroid hormone (Table 1 above ;Nicol & Bruce, 1981) and this occurs at the same time as the increase in T-tubule and terminal cisternae membranes reported here and, in soleus, at the same rime as changes in activation properties and asymmetric charge movement towards values normally seen in faster fibres (Chua & Dulhunty, 1984;Lamb et al, 1984).The maximal velocity of shortening is unaffected by increased thyroid hormone levels, even after prolonged periods of T3 injection (Fitts et al, 1980(Fitts et al, , 1984Montgomery, 1984) so that the long term (> 4 weeks) changes in myosin ATPase activity and myosin isoenzyme (Fitts et al, 1980;Nicol & Bruce, 1981;Nwoye et al, 1982) are hOt reflected in the isotonic contractile properties and presumably do not contribute to changes in isometric contractile properties. It has been suggested that the increase in contraction speed after treatment with thyroid hormone is due to a change in the elastic properties of the fibres (Nicol & Maybee, 1982).…”

“…EDL and soleus muscles from animals (Gold et al, 1970;Fitts et al, 1980Fitts et al, , 1984Nicol & Bruce, 1981). Twitches were invariably more rapid in both EDL and soleus muscles from T3-treated rats but the effect was more marked in~soleus.…”

“…Measurements were ruade of membrane capacity and the amounts of the T-tubule system and terminal cisternae in these fibres. It has been established that excess thyroid hormone leads to changes in the metabolism and physiology of mammalian skeletal muscle: in rat muscles, thyrotoxicosis induces a decrease in the twitch contraction time and an increase in the numbers of small diameter, fast-twitch, red muscle fibres (Gold et al, 1970;Fitts et al, 1980Fitts et al, , 1984Nicol & Bruce, 1981;Hall-Craggs et al, 1983). These changes in the fibres might alter their membrane capacity since fast-twitch fibres normally have 20% more membrane capacity than slow-twitch fibres in rat muscle (Dulhunty & Gage, 1983), 40% more in mouse muscle (Luff & Atwood, 1972), and membrane capacity depends on fibre diameter (Hodgkin & Nakajima, 1972;Dulhunty 0142-4319/86 $03.00 + .12 9 1986 Chapman and Hall Ltd.…”

American Thyroid Association Guide to Investigating Thyroid Hormone Economy and Action in Rodent and Cell Models

“…Detailed analysis of the contractile properties of rat and mouse skeletal muscles requires ex vivo analyses. The slow-twitch SOL muscle has typically been used in studies involving thyroid hormone (689-692) because of the greater responsiveness when compared to the fast-twitch EDL (693). Although contractile properties can be recorded with the muscle left in situ, analysis of isolated muscles in a stimulation chamber allows for greater experimental flexibility (690).…”

A influência do hormônio tireoideano nas proteínas estruturais da banda M no coração e no músculo esquelético de ratos.

“…Esse hormônio executa um papel crucial na diferenciação de características bioquímicas e contráteis do músculo esquelético de vertebrados, como transformação da isoforma de MHC embriônica ou fetal para isoformas adultas (Finkelstein et al, 1991;Gambke et al, 1983). Após o desenvolvimento para a fase adulta, há um processo de maturidade lento que continua a afetar o músculo esquelético durante a vida, resultando em dediferenciação de músculos de fibras lentas e rápidas numa idade avançada (Fitts et al, 1984). No adulto, T3 exerce profundos efeitos na expressão de genes codificantes de isoformas específicas de miosina e outras proteínas contráteis (Caiozzo et al, 1998; Caiozzo e Haddad, 1996;Haddad et al, 1998; Izumo e Mahdavi, 1988).…”