AJP - Renal Physiology, Vol 251, Issue 1 74-F80, Copyright © 1986 by American Physiological Society
System A amino acid transport in incubated muscle: effects of insulin and acute uremia
B. J. Maroni, G. Karapanos and W. E. Mitch
The insulin-stimulated increase in amino acid uptake in most cells and
tissues involves stimulation of system A transport. In muscle the probes
used to study this process have not been specific, making it difficult to
determine whether system A is abnormal in insulin-resistant states, such as
acute renal failure (ARF). To circumvent this problem, we studied
2-(methylamino) isobutyrate (MeAIB) transport. Its specificity for system A
in incubated rat epitrochlearis muscles was documented by showing its
uptake by only one carrier that is sodium dependent and insulin responsive
and that exhibits adaptive regulation in response to starvation. Using this
specific probe we determined whether insulin-stimulated amino acid
transport by system A is impaired by ARF. MeAIB uptake was linear for 3 h
in muscles of ARF and sham-operated (SO) rats. In the absence (basal) or
presence of insulin, MeAIB uptake was significantly lower in ARF, yet the
stimulation by insulin was similar in both groups. Likewise, the insulin
dose-response relationship confirmed that physiological levels of insulin
(less than or equal to 10(2) microU/ml) increased transport by a similar
degree. At greater than or equal to 10(2) microU/ml insulin there was a
plateau in MeAIB transport in ARF but not in SO muscles. Thus basal system
A transport is depressed in ARF, but the stimulation of system A by
physiological levels of insulin is preserved. At pharmacological levels of
insulin system A transport is impaired by ARF.
