Talmadge R J, Mills S, Powers S K, Silverman H
Department of Zoology, Louisiana State University, Baton Rouge 70803.
Respir Physiol. 1994 Oct;98(2):153-64. doi: 10.1016/0034-5687(94)00063-8.
The mammalian diaphragm (Dia) is a unique skeletal muscle because of its chronic contractile activity. Chronically active muscles have higher capacities for glycogen synthesis from lactate and glucose. In this study, the contribution of alanine to glycogen synthesis in the predominantly fast-twitch mouse Dia was determined. Chronically active fast- and slow-twitch muscles from dy2J/dy2J pseudomyotonic mice were also analyzed. Alanine aminotransferase (AlaAT) activity was significantly (P < 0.05) greater in Dia and chronically active gastrocnemius muscle (Gast) than control Gast. 14C-label incorporation into glycogen following in vivo injection of 14C-alanine, was significantly higher in Dia and chronically active Gast than control Gast. A direct incorporation of 14C from 14C-alanine into glycogen is also observed in vitro. The incorporation rate shows a linear concentration dependent relationship and a pH optimum of 6.3. Insulin had no effect on glycogen synthesis from alanine by Dia in vitro. The extensor digitorum longus muscle (EDL) and chronically active EDL and soleus muscle (Sol) had higher rates of glycogen synthesis from alanine than control Sol and Dia. The oxidation of alanine to CO2 was the primary route for alanine metabolism by the Dia. These results demonstrate that the Dia can synthesize glycogen from alanine, but only at low rates.
哺乳动物的膈肌（Dia）是一种独特的骨骼肌，因其具有持续的收缩活动。持续活跃的肌肉从乳酸和葡萄糖合成糖原的能力更强。在本研究中，测定了丙氨酸对以快肌纤维为主的小鼠膈肌糖原合成的贡献。还分析了来自dy2J/dy2J假肌强直小鼠的持续活跃的快肌和慢肌纤维。膈肌和持续活跃的腓肠肌（Gast）中的丙氨酸转氨酶（AlaAT）活性显著（P < 0.05）高于对照腓肠肌。在体内注射14C-丙氨酸后，膈肌和持续活跃的腓肠肌中14C标记掺入糖原的量显著高于对照腓肠肌。在体外也观察到14C-丙氨酸中的14C直接掺入糖原。掺入率呈现线性浓度依赖关系，最适pH为6.3。胰岛素对膈肌体外由丙氨酸合成糖原没有影响。比目鱼肌（Sol）和持续活跃的比目鱼肌以及趾长伸肌（EDL）由丙氨酸合成糖原的速率高于对照比目鱼肌和膈肌。丙氨酸氧化为CO2是膈肌代谢丙氨酸的主要途径。这些结果表明，膈肌可以由丙氨酸合成糖原，但速率较低。
