Transepithelial transport and metabolism of thyrotropin-releasing hormone (TRH) in monolayers of a human intestinal cell line (Caco-2): evidence for an active transport component?

Pharm Res. 1994 Nov;11(11):1575-80. doi: 10.1023/a:1018953603301.

Abstract

Cell culture models for gastrointestinal transport and metabolism are important mechanistic tools. Our studies of Caco-2 monolayers demonstrate heterogeneity in transport characteristics depending on passage number and origin of the cells. In accordance with data obtained in animals and humans, TRH shows a carrier-mediated, saturable transport component, which operates parallel to a passive pathway in Caco-2 cells at passage number 89-99. At low TRH concentrations (< 3 mM) active transport becomes prominent, as demonstrated by the temperature dependence of TRH transport and inhibition experiments. The Michaelis-Menten parameters of the active, saturable transport component are: Km = 1.59 mM and Vmax = 1.84 microM/min. The pH optimum was determined to be at pH 6.0. On the other hand an exclusively paracellular passive route was found with Caco-2 cells at passage number 30-34. These results are also in agreement with observations made by others in cell culture experiments. The aspect of rigorously characterizing the specific Caco-2 clone under investigation is emphasized, especially when active transport mechanisms are suspected.

Publication types

  • Comparative Study

MeSH terms

  • Amino Acid Sequence
  • Biological Transport, Active / physiology
  • Cell Line
  • Humans
  • Intestinal Mucosa / cytology
  • Intestinal Mucosa / metabolism*
  • Molecular Sequence Data
  • Molecular Structure
  • Thyrotropin-Releasing Hormone / metabolism
  • Thyrotropin-Releasing Hormone / pharmacokinetics*

Substances

  • Thyrotropin-Releasing Hormone