신경교차문합(神經交叉吻合)이 근육의 sarcoplasmic reticulum 의 calcium 섭취속도에 미치는 영향
Effect of cross-innervation on the rate of calcium uptake in sarcoplasmic reticulum of slow and fast muscles in cats
Ranvier (1874) described the first systematic investigation of the contraction of the slow and fast muscles. He noted that fast muscles contracted rapidly and required high frequencies of stimulation before complete tetanic fusion occured. In contrast to fast muscles, slow muscles have much slower contraction time and are tetanized at lower frequencies. And thus, functionally, fast muscles are flexor-type muscles. Slow musc1es, on the other hand, function in the maintenance of posture.
Recent results from histochemical and biochemical studies suggest the existence of distinct differences in these two types of muscles. Fast muscles are white, and slow muscles are red in gross appearance (Ranvier, 1874, Fiehn and Peter, 1971). The fact that fast muscles have relatively high myosin-ATPase activity, is attributed to the rapid contraction time (Barany et al., 1965; Barany, 1967; Barnard et al., 1971; Edgerton and Simpson, 1969; Edgerton and Simpson, 1971). Croz and Bucher (1960) and Dawson and Romanul (1964) reported that the levels of activities of the enzymes involved in anaerobic glycolysis are higher in fast muscles than in slow ones. In contrast, slow muscles contain higher activities of enzymes involved in aerobic pathways. Fragmented sarcoplasmic reticulum(FSR) prepared from fast and slow muscles have different calcium accumulating capacities. FSR from slow muscles show slower rate of calcium accumulating capacity, which correlates with a prolonged relaxation time (Sreter, 1964; Sreter, 1969; Ebashi and Lipman, 1962; Fiehn and Peter, 1971).
Recently, nerve cross-innervation experiments in cats demonstrated that when the nerve from a fast muscle (M. flexor digitorum longus, FDL) was made to innervate a slow muscle (M. Soleus) the twitch time of the soleus became shorter than before.
On the other hand, contractions of the FDL muscles cross-innervated by the soleus nerve were markedly prolonged (Buller et al., 1960^^a ; Buller et al., 1960^^b ; Buller and Lewis, 1965; Close, 1964; Eccles et al., 1962 ; Prewitt and Salafsky, 1967). In 1967, McPherson and Tokunaga reported that after cross- innervation of the nerves, the FDL/soleus myoglobin ratio was significantly greater than that of both normal cats or cats after self-innervation of their nerves. Measurements of the activities of two glycolytic enzymes, pyruvic kinase and aldolase, and two
oxidative enzymes, malic dehydrogenase and isocitric dehydrogenase, revealed that the activites of the glycolytic enzymes, which are normally higher in the FDL than in the soleus, decreased in the FDL and increased in the soleus after cross-innervation, while the activities of the oxidative enzymes which are normally higher in the soleus, decreased in the soleus and increased in the FDL by the cross-innervation.
In the above mentioned studies, changes in the motor nerve supply to a muscle can change the histochemical, biochemical, and contractile properties of the muscle. Therefore, the question arises as to whether the calcium uptake by FSR from fast twitch or slow twitch muscles is also changed by cross-innervation. As an approach to this problem, an attempt was made to investigate the effect of cross-innervation on the rate of calcium uptake by FSR prepared from the soleus and FDL of the cat.
In this study, a group of young cats of either sex weighing 1.5-2.0 kg(6 animals) were anesthetized with pentobarbital, 35 mg/kg intraperitoneally, and cross-innervation of the soleus and FDL muscles was performed on one leg and the contralateral leg was served as the control. In another group of cats, the muscles
were self-innervated on one leg and contralateral leg was served as the control. Five to eight months after the operative procedure, the muscle contraction time and half-relaxation time were measured. Subsequently the muscles were removed and fragmented sarcoplasmic reticulum was prepared by differential centrifugation. The calcium uptake was determined at 26℃ according to the method employed by Fiehn and Peter(1971). The calcium uptake was determined at that time after incubation of 30
sec., 1 min., 3 min., 6 min., and 10 min., respectively and aliquots of incubation mixtures containing FSR ware filtered through Millipore filters (pore size, 0.22 μ) and the radioactivity in the filtrates was counted to determine the amount of calcium remaining in the filtrates.
The results obtained are summarized as follows;
1) Cross-innervation of fast and slow muscles of the cats resulted in a prolongation of the FDL twitch time and in a shortening of the soleus twitch time, however, there was no significant changes in twitch time before and after self-innervation of the FDL and soleus muscle.
2) The rate of calcium uptake by FSR increased in soleus but decreased in FDL after cross-innervation. However, after self-innervation of the nerves, the rate of calcium uptake by FSR from both soleus and FDL was not significantly different from that of control.
From the results of this study, it may be concluded that changes in the rate of calcium uptake by FSR from both soleus and FDL muscles take place after cross-innervation in addition to contraction time i.e., cross-innervation produces changes in a fast muscle in both its contractile response and the rate of calcium uptake by FSR toward the characteristics of slow muscle, whereas the slow muscles changes toward those of the fast muscles.