Mayne C N, Sutherland H, Jarvis J C, Gilroy S J, Craven A J, Salmons S
Department of Human Anatomy and Cell Biology, University of Liverpool, United Kingdom.
Am J Physiol. 1996 Jan;270(1 Pt 1):C313-20. doi: 10.1152/ajpcell.1996.270.1.C313.
Chronic electrical stimulation of skeletal muscle at 10 Hz induces fast-to-slow fiber type transformation. Does a lower aggregate amount of activity lead to a less complete transformation, or does it produce the same transformation over a longer time course? We examined this question by subjecting adult rabbit tibialis anterior and extensor digitorum longus muscles to continuous stimulation at 2.5 Hz for 2-12 wk. Most of the fibers acquired the histochemical and immunocytochemical characteristics of type 2A, not type 1, fibers. There was a corresponding rise in oxidative activity, but this was accompanied by a marked decline in anaerobic glycolysis. The activities of hexokinase and 3-oxoacid CoA-transferase stopped increasing after 2 wk, glutamate oxaloacetate transaminase after 4 wk, and beta-hydroxyacyl-CoA dehydrogenase after 6 wk of stimulation. Succinate dehydrogenase, citrate synthase, lactate dehydrogenase, and creatine phosphokinase continued to change up to 12 wk of stimulation. Changes in enzyme activity were not as rapid or as marked as those observed for stimulation at 10 Hz, and none showed the typical two-phase response of oxidative enzyme activities to stimulation at 10 Hz. The latter may therefore be dependent on induction of type 1 myosin isoforms.
以10赫兹的频率对骨骼肌进行慢性电刺激会诱导快肌纤维向慢肌纤维类型转变。较低的总活动量会导致转变不那么完全，还是会在更长的时间过程中产生相同的转变呢？我们通过对成年兔的胫骨前肌和趾长伸肌进行2.5赫兹的持续刺激，持续2至12周，来研究这个问题。大多数纤维获得了2A型而非1型纤维的组织化学和免疫细胞化学特征。氧化活性相应增加，但同时无氧糖酵解显著下降。刺激2周后，己糖激酶和3-氧代酸辅酶A转移酶的活性停止增加，4周后谷氨酸草酰乙酸转氨酶停止增加，6周后β-羟酰基辅酶A脱氢酶停止增加。琥珀酸脱氢酶、柠檬酸合酶、乳酸脱氢酶和肌酸磷酸激酶的活性在刺激12周时仍持续变化。酶活性的变化不如在10赫兹刺激时观察到的那样迅速或显著，且没有一种酶表现出氧化酶活性对10赫兹刺激典型的双相反应。因此，后者可能依赖于1型肌球蛋白同工型的诱导。
