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Vol. 294, Issue 2, 466-472, August 2000
2-Adrenergic Receptors Stimulate
Oligopeptide Transport in a Human Intestinal Cell Line1
Institut National de la Santé et de la Recherche
Médicale, Faculté X. Bichat, Paris (F.B., J.-J.M., M.L.,
C.R.); Institut National de la Santé et de la Recherche
Médicale, Institut Louis Bugnard, Toulouse (H.P.); and
Unité Propre de Recherches de I'Enseignement Supérieure,
Faculté de Pharmacie, Chatenay-Malabry, France (F.B.,
R.F.)
Di- and tripeptides, as well as peptidomimetic drugs such as cephalexin
(CFX), are absorbed by enterocytes via the oligopeptide transporter
PepT1. We recently showed that the
2-adrenergic agonist clonidine increases CFX absorption in anaesthetized rats. Herein, we
investigated whether
2-adrenergic receptors can directly
affect PepT1 activity in a clone of the differentiated human intestinal cell line Caco-2 (Caco-2 3B) engineered to stably express
2A-adrenergic receptors at a density similar to that
found in normal mucosa. Measurement of CFX fluxes across cell
monolayers cultured on transwell filters demonstrated that the
2-agonists clonidine and UK14304 caused a 2-fold
increase of CFX transport in Caco-2 3B cells, but not in Caco-2
(expressing PepT1 but not
2-adrenergic receptors) or in
the HT29 19A clone (expressing
2-adrenergic receptors
but not PepT1). The stimulatory effect of clonidine was abolished by
glycyl-sarcosine (a competitor for the transporter) and blocked by
yohimbine or RX821002 (
2-antagonists). Analysis of the
kinetics of CFX transport in control and clonidine-treated Caco-2 3B
cells showed that clonidine increased Vmax
of CFX transport without changing Km.
Clonidine action was abolished by colchicine but not altered by
amiloride, demonstrating that microtubule integrity but not
Na+/H+ exchanger activity is necessary for the
effect of
2-agonists to occur. In conclusion, clonidine
can directly activate
2-adrenergic receptors located on
epithelial cells. The precise molecular mechanisms whereby these
receptors modulate PepT1 activity remain to be elucidated but an
increased translocation to the apical membrane of preformed cytoplasmic
transporter molecules is likely to be involved.
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