中文摘要：

目的研究地塞米松对体外培养的骨骼肌肌管内长寿命蛋白降解的影响及其可能的作用机制。方法无菌分离（2日龄）Wistar大鼠双下肢肌肉．组织块法培养、增殖、传代纯化成肌细胞．融合形成肌管，使用L—C3，5-^3H]-酪氨酸标记肌管长寿命蛋白后，随机分成两组。A组：分别用不含地塞米松（对照组）或含地塞米松10nmol／L（A1组）、100nmol／L（A2组）、1000nmol／L（A3组）的培养液培养肌管，12、24、36和48h后使用液体闪烁计数仪测定培养液和细胞内L-[3，5-^3H]-酪氨酸的含量，计算肌管长寿命蛋白的降解率。B组：分别用含蛋白酶体抑制剂MG132（50μmol／L，B1组）或含MG132（50μmol／L）和地塞米松100nmol／L（B2组）的培养液培养肌管24h，相同方法测定肌管长寿命蛋白降解率。结果A1、A2和A3组长寿命蛋白降解率均较对照组显著增加，差异有显著性（P均〈0．01）。A2组和A3组长寿命蛋白降解率均较A1组显著增加，差异有显著性（P均〈0．01）。A2组和A3组比较．长寿命蛋白降解率差异无显著性（P〉0．05）。B1组长寿命蛋白降解率较对照组（24h）降低明显，B2组长寿命蛋白降解率较A2组（24h）显著降低，差异均有显著性（P均〈0．01）。结论泛素-蛋白酶体途径是骨骼肌肌管长寿命蛋白的重要降解途径之一。地塞米松能通过激活肌管内泛素-蛋白酶体途径而增强长寿命蛋白的降解，此效应在一定范围内呈量效依赖关系。

英文摘要：

Objective To study the effect of dexamethasone on degradation of long - lived protein in myotubes and to elucidate its possible mechanism. Methods After isolating skeletal muscles of rat＇s hind limb under sterile condition, the myoblasts were proliferated in tissue -block culture. After being passaged and purified, the myoblasts fused into myotubes. The protein in myotubes was radiolabelled with L -[3,5-^3H]-tyrosine, and then the myotubes were divided into two groups. In group A,the myotubes were cultured in Dubbecco＇s modified Eagle＇s medium （DMEM） containing 10% fetal bovine serum （FBS） and 2 mmol/L tyrosine without dexamethasone （control group）, with dexamethasone 10 nmol/L （group A1）, dexamethasone 100 nmol/L （group A2）, and dexamethasone 1 000 nmol/L （group A3）, respectively. The amounts of L-[3,5 -^3H]-tyrosine in culture medium and cells were determined and the degradation rates of longlived protein were calculated at 12, 24, 36, 48 hours of culture. In group B, the myotubes were cultured in DMEM containing 10% FBS and 2 mmol/L tyrosine with 50 μmol/L protcasome inhibitor MG132 （group B1）, or 50 btmol/L MG132 and 100 nmol/L dexamethasone （group B2）. Proteolytic rates of protein were calculated with the same way as group A at 24 hours. Results The proteolytic rate of long - lived protein in group A1, group A2 and group A3 was all increased significantly compared with that in control group （all P〈0. 01）, and that in group A2 and A3 rose markedly compared with that in group A1 （both P〈0. 01 ）, respectively. There was no statistically significant difference between group A2 and group A3 （P〉0. 05）. Proteolytic rate of long - lived protein in group B1 was significantly lower than that in control group （P〈0. 01）. The degradation rate of long- lived protein in group B2 was markedly lower than that in group A2 （P〈0. 01）. Conclusion The results suggest that the ubiquitin- proteasome system is one of the important pathways of degradation of long -