AJP - Cell Physiology, Vol 261, Issue 4 C608-C613, Copyright © 1991 by American Physiological Society
Effects of phenylarsine oxide on insulin-stimulated system A amino acid uptake in skeletal muscle
E. J. Henriksen
Department of Exercise and Sport Sciences, University of Arizona, Tucson 85721.
The role of vicinal sulfhydryls in the stimulation by insulin of system A
amino acid uptake in mammalian skeletal muscle was investigated. Neutral
amino acid uptake via system A carriers was assessed using the
nonmetabolizable analogue alpha-(methylamino)isobutyric acid (MeAIB).
Phenylarsine oxide (PAO), a trivalent arsenical that interacts with vicinal
sulfhydryls, at 40 microM inhibited basal and insulin-stimulated (2 mU/ml)
MeAIB uptake in rat epitrochlearis muscles by approximately 50% and
approximately 80%, respectively. No significant changes in the ATP level or
in the lactate-to-pyruvate ratio were observed. Both inhibitory effects
were completely preventable by coincubation with dimercaptopropanol, a
vicinal dithiol, indicating the effects were mediated specifically by
interactions with vicinal sulfhydryls. Stimulation of MeAIB uptake by the
insulin-mimicker vanadate (10 mM) or by insulin-like growth factor I
(IGF-I, 20 nM) was also inhibited by 80-90% by PAO. Kinetic analysis showed
that PAO decreased the apparent Vmax for basal and insulin-stimulated MeAIB
uptake without altering the apparent Km. MeAIB uptake already maximally
stimulated by insulin was rapidly (half-time = approximately 10 min)
reversed by the addition of PAO so that the rate of MeAIB uptake was the
same as in muscles incubated throughout with insulin and PAO. These results
implicate a major role for vicinal sulfhydryls in the stimulation by
insulin of amino acid uptake via system A carriers in skeletal muscle and
suggest that the site of action of PAO on this system is distal to the
insulin receptor, possibly at the carrier molecule itself.
