INSULIN AND NA-DEPENDENT ALANINE TRANSPORT IN SKELETAL-MUSCLE OF OBESE ZUCKER (FA FA) RATS/

Obese Zucker (fa/fa) rat skeletal muscle is characterized by a reduced rate of muscle protein deposition possibly due to alterations in amin o 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 transpor t independent of cellular metabolism. Initial rates of alanine transpo rt were measured in the presence and absence of Na using a rapid filtr ation technique, and the properties of membranes from control and maxi mally insulin-treated lean and obese Zucker rats were studied. For lea n rats, the maximal stimulation (V-max) for Na-dependent alanine trans port was 207 pmol.mg(-1).s(-1), and the half-maximal affinity constant (K-1/2) was 2.3 mM. Insulin treatment increased the V-max to 387 pmol .mg(-1).s(-1) with no changes in K-1/2. For the obese rats, the V-max for Na-dependent alanine transport was 248 pmol.mg(-1).s(-1), and the K-1/2 was 2.8 mM. These values were not changed by insulin treatment. Thus Na-dependent alanine transport in obese rat skeletal muscle is re sistant to stimulation by insulin; this alteration may contribute to t he abnormal muscle protein metabolism observed in these animals.