Metabolic recovery of mouse extensor digitorum longus and soleus muscle

Abstract

Heat produced by a 1-s isometric tetanus of mouse extensor digitorum longus muscle (EDL; n = 6) and a 1.5-s isometric tetanus of soleus muscle (n = 7) was measured with thermopiles at 20 degrees C, and separated into initial heat (I) and recovery heat (R). In EDL the initial heat was 190 +/- 40 (SD) mJ g-1 and in soleus 52 +/- 9 (SD) mJ g-1. The recovery heat production rate immediately following the tetanus was almost zero in both muscles. It rose in 12 +/- 6 s (EDL) and in 30 +/- 3 s (soleus) to a maximum, to decrease thereafter monoexponentially with a time constant of 30.7 +/- 5.7 s (EDL) and 41.7 +/- 7.2 s (soleus). The measured recovery ratio (R/I) differed between EDL (0.95 +/- 0.14) and soleus (1.54 +/- 0.22). The value for soleus muscles was significantly different from the theoretical value of 1.13. EDL muscles were freeze-clamped at rest (n = 10) and during the recovery phase, 1 min after the onset of the tetanus (n = 10), to determine lactate and creatine phosphate. It was found that no significant amount of net lactate was produced. The amount of creatine phosphate reformed corresponded to the recovery heat produced. The results suggest that metabolic recovery after short tetani of EDL and soleus muscles occurs predominantly through oxidative phosphorylation, but knowledge of respiratory control in the living cell is insufficient to explain its slow onset immediately following contraction and the finding that EDL recovers faster than soleus.

The effects of ATP on the contractions of rat and mouse fast skeletal muscle

“…In our experiments with rodent fast muscles, the opposite effect to that observed in slow and mixed skeletal muscles was seen: the amplitude of contractions decreased under hypothermia in both rat and mouse EDL. There are several studies on the temperature‐dependence of the contractile apparatus of slow skeletal muscles with conflicting data on the muscles of the same animals . Thus, on the one hand, the temperature‐dependence of slow muscle fibers in rats is much more pronounced than that of fast muscle fibers, while on the other hand the temperature‐sensitivity of myosin of slow rat muscle fibers does not differ from the fast ones …”

The energetic cost of activation in mouse fast‐twitch muscle is the same whether measured using reduced filament overlap or N‐benzyl‐p‐toluenesulphonamide

“…The mass/length ratio of muscles used in the current study (0.33 AE 0.02; n = 26) was much lower than the maximum compatible with adequate oxygenation over the range of rates of resting oxygen consumption for EDL from the literature. The rate of oxidative metabolism transiently increases following a tetanus (Leijendekker & Elzinga 1990) and the time course of PO 2 at the muscle centre was calculated as described previously (Barclay 2005). The analysis was extended to calculate the time course of PO 2 at the muscle centre following a 1-s tetanus (Fig.…”

“…When stimulated maximally, Q BTS was $40% of Q 0 at both 20 and 30°C (Table 1). Leijendekker & Elzinga (1990) measured the maximum rate of post-tetanic heat output to be 3 mW g )1 at 20°C, which was reached $10 s after a 1-s tetanus. Further these values did not differ significantly from the values determined using the pre-stretch method with the same stimulation frequency.…”

Energetics of fast‐ and slow‐twitch muscles of the mouse.

“…Heat from processes associated with resynthesis of ATP ('recovery' heat) has a time course that, in skeletal muscle, is quite distinct from that of initial heat production. Whereas initial heat is produced almost entirely within the time of contraction, recovery heat production in mouse soleus and EDL muscles at 21°C does not commence until several seconds after relaxation and requires 2-3 min to complete (Leijendekker & Elzinga, 1990). In addition, its maximum rate is only 5% of the heart rate.…”