King P A, Betts J J
Department of Medicine, University of Vermont, Burlington 05405.
Am J Physiol. 1994 Dec;267(6 Pt 2):R1606-10. doi: 10.1152/ajpregu.1994.267.6.R1606.
Obese Zucker (fa/fa) rat skeletal muscle is characterized by a reduced rate of muscle protein deposition possibly due to alterations in amino acid transport. The purpose of the present study was to investigate alanine transport in plasma membrane vesicles from skeletal muscle of lean and obese Zucker rats, facilitating the study of alanine transport independent of cellular metabolism. Initial rates of alanine transport were measured in the presence and absence of Na using a rapid filtration technique, and the properties of membranes from control and maximally insulin-treated lean and obese Zucker rats were studied. For lean rats, the maximal stimulation (Vmax) for Na-dependent alanine transport was 207 pmol.mg-1.s-1, and the half-maximal affinity constant (K1/2) was 2.3 mM. Insulin treatment increased the Vmax to 387 pmol.mg-1.s-1 with no changes in K1/2. For the obese rats, the Vmax for Na-dependent alanine transport was 248 pmol.mg-1.s-1, and the K1/2 was 2.8 mM. These values were not changed by insulin treatment. Thus Na-dependent alanine transport in obese rat skeletal muscle is resistant to stimulation by insulin; this alteration may contribute to the abnormal muscle protein metabolism observed in these animals.
肥胖 Zucker（fa/fa）大鼠的骨骼肌具有肌肉蛋白质沉积速率降低的特征，这可能是由于氨基酸转运的改变所致。本研究的目的是研究瘦型和肥胖 Zucker 大鼠骨骼肌质膜囊泡中的丙氨酸转运，以促进对独立于细胞代谢的丙氨酸转运的研究。使用快速过滤技术在有和没有 Na 的情况下测量丙氨酸转运的初始速率，并研究来自对照以及最大胰岛素处理的瘦型和肥胖 Zucker 大鼠的膜特性。对于瘦型大鼠，Na 依赖性丙氨酸转运的最大刺激（Vmax）为 207 pmol·mg-1·s-1，半最大亲和力常数（K1/2）为 2.3 mM。胰岛素处理使 Vmax 增加到 387 pmol·mg-1·s-1，而 K1/2 没有变化。对于肥胖大鼠，Na 依赖性丙氨酸转运的 Vmax 为 248 pmol·mg-1·s-1，K1/2 为 2.8 mM。这些值不受胰岛素处理的影响。因此，肥胖大鼠骨骼肌中 Na 依赖性丙氨酸转运对胰岛素刺激具有抗性；这种改变可能导致在这些动物中观察到的异常肌肉蛋白质代谢。
