Abstract
Although the morphologic and enzymatic acquisitions associated with enterocytic differentiation have been extensively investigated, little is 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 crypt cell. Proline uptake involves both Na +-independent non-saturable diffusion and Na +-dependent components. The Na +-dependent transport of proline is sensitive to the pH and is inhibited by hydroxyproline, glycine, alanine, and MeAIB. Non-α amino acids, such as β-alanine and γ-aminobutyric acid, do not compete with proline, whereas leucine is a weak inhibitor. Therefore, proline transport appears to occur through the system A, whereas the intestinal specific systems (B and IMINO) are not involved in this process. These observations suggest that these two systems are either absent or expressed at a very low level in this undifferentiated epithelial cell line.
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