Welle S, Bhatt K, Thornton C
Department of Medicine, University of Rochester, New York 14620, USA.
Am J Physiol. 1996 Feb;270(2 Pt 1):E224-9. doi: 10.1152/ajpendo.1996.270.2.E224.
The myofibrillar protein synthesis rate in old human skeletal muscle is slower than that in young adult muscle. To examine whether this difference in protein synthesis rate is explained by reduced availability of the mRNAs that encode the most abundant myofibrillar proteins, we determined relative hybridization signals from probes for actin mRNA, myosin heavy chain mRNA, and total polyadenylated RNA in vastus lateralis muscle biopsies taken from young (22- to 31-yr-old) and old (61- to 74-yr-old) human subjects. The mean fractional rate of myofibrillar synthesis was 38% slower in the older muscles, as determined by incorporation of a stable isotope tracer. Total actin and myosin heavy chain mRNAs, and polyadenylated RNA, were determined using slot-blot assays. Isoform-specific determinations of alpha-actin mRNA, type I myosin heavy chain mRNA, and type IIa myosin heavy chain mRNA were done with ribonuclease protection assays. Hybridization signals were expressed relative to tissue DNA content. There was no difference between age groups in total polyadenylated RNA or in any of the specific mRNAs. We conclude that the slower myofibrillar synthesis rate in older muscle is not caused by reduced mRNA availability.
老年人骨骼肌中肌原纤维蛋白的合成速率比年轻成年人的肌肉慢。为了研究蛋白质合成速率的这种差异是否是由于编码最丰富的肌原纤维蛋白的mRNA可用性降低所致，我们测定了从年轻（22至31岁）和老年（61至74岁）人体受试者的股外侧肌活检样本中提取的肌动蛋白mRNA、肌球蛋白重链mRNA和总聚腺苷酸化RNA探针的相对杂交信号。通过稳定同位素示踪剂的掺入测定，老年肌肉中肌原纤维合成的平均分数速率慢38%。使用狭缝印迹分析法测定总肌动蛋白和肌球蛋白重链mRNA以及聚腺苷酸化RNA。用核糖核酸酶保护分析法对α-肌动蛋白mRNA、I型肌球蛋白重链mRNA和IIa型肌球蛋白重链mRNA进行亚型特异性测定。杂交信号相对于组织DNA含量进行表达。各年龄组之间的总聚腺苷酸化RNA或任何特定mRNA均无差异。我们得出结论，老年肌肉中肌原纤维合成速率较慢并非由mRNA可用性降低所致。
