Abstract
The possible role of the gamma-glutamyl cycle in the transport of amino acids, using the Caco-2 cell monolayer as an in vitro model of the small intestine, has been investigated.
The transport of [2-
3H]glycine and [2-
3H]glycylglycine through the Caco-2 monolayer has been shown to occur by two modes of action.
Active transport is unidirectional from apical to basolateral region and is a carrier mediated system. The enzyme gamma-glutamyl transpeptidase seems to be involved in this process, since when the enzyme is inhibited, the active transport is also inhibited. However transport still takes place, and this occurs by a slower non-active process, which is bidirectional and is mediated by passive diffusion.
The rate of transport of [2-
3H]glycylglycine and [2-
3H]glycine were 585 (±24) and 287 (±16) pmolcm
−2min
−1 respectively, while the non-active transport takes place at 87 (±6) pmolcm
−2min
−1. Thus, amino acid translocation in Caco-2 cells is shown to occur by two methods, one of which involves the gamma-glutamyl cycle.