TY - JOUR T1 - α<sub>2</sub>-Adrenergic Receptors Stimulate Oligopeptide Transport in a Human Intestinal Cell Line JF - Journal of Pharmacology and Experimental Therapeutics JO - J Pharmacol Exp Ther SP - 466 LP - 472 VL - 294 IS - 2 AU - Françoise Berlioz AU - Jean-José Maoret AU - Hervé Paris AU - Marc Laburthe AU - Robert Farinotti AU - Claude Rozé Y1 - 2000/08/01 UR - http://jpet.aspetjournals.org/content/294/2/466.abstract N2 - 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 α2-adrenergic agonist clonidine increases CFX absorption in anaesthetized rats. Herein, we investigated whether α2-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 α2A-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 α2-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 α2-adrenergic receptors) or in the HT29 19A clone (expressing α2-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 (α2-antagonists). Analysis of the kinetics of CFX transport in control and clonidine-treated Caco-2 3B cells showed that clonidine increased Vmaxof 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 α2-agonists to occur. In conclusion, clonidine can directly activate α2-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. The American Society for Pharmacology and Experimental Therapeutics ER -