AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 6 1606-R1610, Copyright © 1994 by American Physiological Society
Insulin and Na-dependent alanine transport in skeletal muscle of obese Zucker (fa/fa) rats
P. A. King and J. J. Betts
Department of Medicine, University of Vermont, Burlington 05405.
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.
