Insulin and glucagon stimulation of amino acid transport in isolated rat hepatocytes. Synthesis of a high affinity component of transport.

M Fehlmann,A Le Cam,P Freychet

doi:10.1016/s0021-9258(19)86726-1

Abstract

Insulin and glucagon stimulate amino acid transport in freshly prepared suspensions of isolated rat hepatocytes. The kinetic properties of alpha-amino[1-14C]isobutyric acid (AIB) transport were investigated in isolated hepatocytes following stimulation by either hormone in vitro. In nonhormonally treated cells (i.e. basal state), saturable transport occurred mainly through a low affinity (Km approximately equal to 40 mM) component. In insulin or glucagon-treated hepatocytes, saturable transport occurred through both a low affinity component (similar to that observed in the basal state) and a high affinity (Km approximately equal to 1 mM) component. At low AIB concentrations (less than 0.5 mM), insulin and glucagon at maximally stimulating doses increased AIB uptake about 2-fold and 5-fold, respectively. The high affinity component induced by either hormone exhibited the properties of the A (alanine preferring) mediation of amino acid transport. This component required 2 to 3 h for maximal expression, and its emergence was completely prevented by cycloheximide. Half-maximal stimulation was elicited by insulin at about 3 nM and by glucagon at about 1 nM. Dibutyryl cyclic AMP mimicked the glucagon effect and was not additive to it at maximal stimulation. Maximal effects of insulin and glucagon, or insulin and dibutyryl cyclic AMP, were additive. We conclude that insulin and glucagon can modulate amino acid entry in hepatocytes through the synthesis of a high affinity transport component.

Highlights

From the Groupe de Recherches sur les Hormones Polypeptidiques de la SantP et de la Recherche Mkdicale, U 145, and the Laboratory (Pasteur), Chemin de Vallombrose, 06034 Nice Cedex, France et la Physiopathologie
We show that insulin and glucagon promote the synthesis of a high affinity component of amino acid transport
At 30 mM AIB, insulin increased the initial rate of uptake about 2-fold, but the effect of glucagon was less than the effect of insulin and much less prominent than that observed at 0.1 mM AIB

Summary

Introduction

From the Groupe de Recherches sur les Hormones Polypeptidiques de la SantP et de la Recherche Mkdicale, U 145, and the Laboratory (Pasteur), Chemin de Vallombrose, 06034 Nice Cedex, France et la Physiopathologie. Insulin and glucagon stimulate amino acid transport in freshly prepared suspensions of isolated rat hepatocytes. The kinetic properties of a-amino[l-%]isobutyric acid (AIB) transport were investigated in isolated hepatocytes following stimulation by either hormone in vitro. In insulin or glucagon-treated hepatocytes, saturable transport occurred through both a low affinity component (similar to that observed in the basal state) and a high affinity The high affinity component induced by either hormone exhibited the properties of the A (alanine preferring) mediation of amino acid transport. This component required 2 to 3 h for maximal expression, and its emergence was completely prevented by cycloheximide. Prepared suspensions of isolated rat hepatocytes have been found suitable for investigating various aspects of transport kinetics under basal and hormone-stimulated conditions, and for delineating the transport system affected by the hormonal stimulation [11,12,13,14,15,16]

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Results

Conclusion