Influence of insulin on amino acid uptake by lung slices

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Abstract
The transport of amino acids by rat lung slices was examined using mainly 14C-labeled .alpha.-aminoisobutyric acid ([14C]AIB) as a nonmetabolized amino acid. [14C]AIB is accumulated by the lung in an energy-dependent fashion against a concentration gradient. The uptake is saturable, stereospecific and follows Michaelis-Menten kinetics suggesting enzyme or carrier mediation across the plasma membrane. Insulin increases the uptake of [14C]AIB and insulin plus glucose increases its uptake even more. The diffusion constant (KD) in the presence of glucose, insulin or glucose plus insulin is the same, 0.29 h-1; the Vmax is also the same, 83.0 mmol.cntdot.1-1.cntdot.h-1, under these 3 conditions. The apparent Km is 14.0 mM with glucose, 9.0 mM with insulin and 4.0 mM in the presence of glucose and insulin. The uptake of [14C]AIB is increased by insulin, and insulin plus glucose, and, based on this kinetic analysis, this is due to an increased affinity of the transport sites for AIB (decreased Km, unchanged Vmax and KD).

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