Holeček M, Mičuda S
Department of Physiology and Department of Pharmacology, Faculty of Medicine in Hradec Kralove, Charles University, Hradec Kralove, Czech Republic.
Physiol Res. 2017 Dec 20;66(6):959-967. doi: 10.33549/physiolres.933638. Epub 2017 Sep 22.
We have investigated amino acid concentrations and protein metabolism in musculus extensor digitorum longus (EDL, fast-twitch, white muscle) and musculus soleus (SOL, slow-twitch, red muscle) of rats sacrificed in the fed state or after one day of starvation. Fractional protein synthesis rates (FRPS) were measured using the flooding dose method (L-[3,4,5-3H]phenylalanine). Activities of two major proteolytic systems in muscle (the ubiquitin-proteasome and lysosomal) were examined by measurement of chymotrypsin like activity of proteasome (CTLA), expression of ubiquitin ligases atrogin-1 and muscle-ring-finger-1 (MuRF-1), and cathepsin B and L activities. Intramuscular concentrations of the most of non-essential amino acids, FRPS, CTLA and cathepsin B and L activities were in postprandial state higher in SOL when compared with EDL. The differences in atrogin-1 and MuRF-1 expression were insignificant. Starvation decreased concentrations of a number of amino acids and increased concentrations of valine, leucine, and isoleucine in blood plasma. Starvation also decreased intramuscular concentrations of a number of amino acids differently in EDL and SOL, decreased protein synthesis (by 31 % in SOL and 47 % in EDL), and increased expression of atrogin-1 and MuRF-1 in EDL. The effect of starvation on CTLA and cathepsin B and L activities was insignificant. It is concluded that slow-twitch (red) muscles have higher rates of protein turnover and may adapt better to brief starvation when compared to fast-twitch (white) muscles. This phenomenon may play a role in more pronounced atrophy of white muscles in aging and muscle wasting disorders.
我们研究了在喂食状态下或饥饿一天后处死的大鼠的趾长伸肌（EDL，快肌，白色肌肉）和比目鱼肌（SOL，慢肌，红色肌肉）中的氨基酸浓度和蛋白质代谢。使用灌流剂量法（L-[3,4,5-³H]苯丙氨酸）测量蛋白质合成率（FRPS）。通过测量蛋白酶体的糜蛋白酶样活性（CTLA）、泛素连接酶atrogin-1和肌肉环指蛋白-1（MuRF-1）的表达以及组织蛋白酶B和L的活性，检测肌肉中两个主要蛋白水解系统（泛素-蛋白酶体和溶酶体）的活性。与EDL相比，大多数非必需氨基酸的肌肉内浓度、FRPS、CTLA以及组织蛋白酶B和L的活性在餐后状态下SOL中更高。atrogin-1和MuRF-1表达的差异不显著。饥饿降低了血浆中多种氨基酸的浓度，增加了缬氨酸、亮氨酸和异亮氨酸的浓度。饥饿还使EDL和SOL中多种氨基酸的肌肉内浓度以不同方式降低，降低了蛋白质合成（SOL中降低31%，EDL中降低47%），并增加了EDL中atrogin-1和MuRF-1的表达。饥饿对CTLA以及组织蛋白酶B和L活性的影响不显著。得出的结论是，与快肌（白色）相比，慢肌（红色）具有更高的蛋白质周转率，并且可能对短期饥饿有更好的适应性。这种现象可能在衰老和肌肉萎缩性疾病中白色肌肉更明显的萎缩中起作用。
