title: Choline uptake in human intestinal Caco-2 cells is carrier-mediated.
abstract: The objective of the current investigation was to examine the transport characteristics of choline, an endogenous quaternary ammonium compound, into human intestinal Caco-2 cells; the transport of choline has not been characterized in human intestine. The cellular accumulation of choline was independent of an inwardly directed Na(+) gradient and demonstrated temperature dependence and saturability. Using the initial uptake rates, choline accumulation was best characterized by a Michaelis-Menten equation and a diffusion component with a K(m) and V(max) of 110 +/- 3 micro mol/L and 2800 +/- 250 pmol/(mg protein. 10 min), respectively. Choline uptake was significantly inhibited by an excess of choline itself and by hemicholinium-3, a structural analog of choline. However other hydrophilic organic cations, such as tetraethylammonium (TEA) and N-methylnicotinamide (NMN), did not affect choline uptake in Caco-2 cells. Additionally, two typical p-glycoprotein substrates, daunomycin and verapamil, both inhibited choline accumulation. However the opposite was not true: choline did not inhibit DNM accumulation in Caco-2 cells. These results indicate the presence of a carrier-mediated transport system for choline in Caco-2 cells. The substrate specificity of this carrier is unlike that seen in the rat intestinal epithelium, and the human transport protein is distinct from those for TEA and NMN. P-glycoprotein substrates may inhibit choline uptake through specific or nonspecific interactions with the choline transporter.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo, The State University of New York, Amherst, NY 14260, USA.
authors.forename: Amrita V
authors.initials: AV
authors.lastname: Kamath
authors.forename: Inger M
authors.initials: IM
authors.lastname: Darling
authors.forename: Marilyn E
authors.initials: ME
authors.lastname: Morris
mesh_terms: D018938:Caco-2 Cells; D002352:Carrier Proteins / Q000378:metabolism*; D002794:Choline / Q000493:pharmacokinetics*; D003630:Daunorubicin / Q000494:pharmacology; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology; D007700:Kinetics; D026901:Membrane Transport Proteins / Q000378:metabolism; D009536:Niacinamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D019789:Tetraethylammonium / Q000494:pharmacology; D013997:Time Factors; D014700:Verapamil / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; D026901:Membrane Transport Proteins; C065637:choline transporter; D009536:Niacinamide; D019789:Tetraethylammonium; D012964:Sodium; D014700:Verapamil; D002794:Choline; C008472:N-methylnicotinamide; D003630:Daunorubicin