title: Mechanism of L-alpha-methyldopa transport through a monolayer of polarized human intestinal epithelial cells (Caco-2).
abstract: The Caco-2 model system (Hidalgo et al., Gastroenterology, 96:736-749, 1989), which is a monolayer of polarized intestinal epithelial cells grown onto a porous polycarbonate membrane, was used to study the mechanism of transcellular transport of an antihypertensive agent, L-alpha-methyldopa (L-alpha-MD). The results showed that the transport of L-alpha-MD was pH, glucose, concentration, and temperature dependent, and it could be inhibited by metabolic inhibitors (e.g., 2,4-dinitrophenol) and by amino acids (e.g., L-phenylalanine) which have an affinity for the large neutral amino acid (LNAA) carrier. In addition, the apparent kinetic constants describing the transcellular transport of L-alpha-MD were altered depending on the time interval between feeding the cells and the transport experiments (postfeeding time, PFT). The apparent maximum carrier flux (Jmax) of L-alpha-MD was significantly increased (from 155 to 547 pmol/mg protein/min) when PFT was prolonged from 8.5 to 56 hr. These results indicated that the transcellular transport of L-alpha-MD through the polarized Caco-2 cell monolayer was carrier mediated via the LNAA carrier. The similarities in the characteristics of L-alpha-MD transport exhibited by the Caco-2 model system and other intestinal models in vitro further substantiate the usefulness of this cell culture model for studying the intestinal transport of nutrients and drugs.
authors.affiliation: Department of Pharmaceutical Chemistry, University of Kansas, Lawrence 66045.
authors.forename: M
authors.initials: M
authors.lastname: Hu
authors.forename: R T
authors.initials: RT
authors.lastname: Borchardt
mesh_terms: D019297:2,4-Dinitrophenol; D000959:Antihypertensive Agents / Q000493:pharmacokinetics*; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D004140:Dinitrophenols / Q000494:pharmacology; D004847:Epithelial Cells; D004848:Epithelium / Q000378:metabolism; D005947:Glucose; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D007422:Intestines / Q000166:cytology; D007980:Levodopa / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D008954:Models, Biological; D010649:Phenylalanine / Q000494:pharmacology; D011485:Protein Binding; D013696:Temperature
chemical_list: D000959:Antihypertensive Agents; D002352:Carrier Proteins; D004140:Dinitrophenols; D007980:Levodopa; D010649:Phenylalanine; D005947:Glucose; C035420:levodopa methyl ester; D019297:2,4-Dinitrophenol