INVOLVEMENT OF SYSTEM-A IN PROLINE TRANSPORT IN THE INTESTINAL CRYPT-LIKE CELL-LINE IEC-17

Although the morphologic and enzymatic acquisitions associated with en terocytic differentiation have been extensively investigated, little i s known about the changes in amino acid transport during this process. The transport of proline was examined in the rat epithelial cell line IEC-17, which presents the characteristics of an undifferentiated cry pt cell. Proline uptake involves both Na+-independent non-saturable di ffusion and Na+- dependent components. The Na+-dependent transport of proline is sensitive to the pH and is inhibited by hydroxyproline, gly cine, alanine, and MeAIB. Non-alpha amino acids, such as beta-alanine and gamma-aminobutyric acid do not compete with proline, whereas leuci ne is a weak inhibitor. Therefore, proline transport appears to occur through the system A, whereas the intestinal specific systems (B and I MINO) are not involved in this process. These observations suggest tha t these two systems are either absent or expressed at a very low level in this undifferentiated epithelial cell line.