Chloride-dependence of amino acid transport in rabbit ileum.
Chloride-dependence of influx across the brush-border membrane of distal rabbit ileum was examined for beta-alanine, 2-methylaminoisobutyric acid (MeAIB), leucine, lysine, proline and D-glucose. Influx of leucine at 2 mM and of D-glucose at 0.5 mM was chloride-independent indicating that substitution of isethionate for chloride has no unspecific effect on sodium gradient driven transport processes. In contrast influx of beta-alanine and MeAIB was totally dependent on the presence of chloride ions. In the absence of chloride, proline transport was reduced to 20% of its control level. This remaining transport can be accounted for by the function of the carrier of alpha-amino-monocarboxylic acids. Transport of leucine at 0.1 mM was reduced by absence of chloride. This is in accordance with the observation of leucine transport by the beta-alanine carrier. The kinetics of chloride and sodium activation of transport of MeAIB were examined at 1 mM MeAIB. Chloride activation was characterized by a Hill coefficient of 1 and a K1/2 of 23.5 mM, and sodium activation by a Hill coefficient of 2 and a K1/2 of 51 mM. Thus cotransport of chloride with an imino acid would be compatible with the known rheogenic nature of this transport. This study adds the imino acid carrier and the beta-alanine carrier to the group of chloride-dependent, epithelial amino acid transport systems.
Munck
L K
LK
Bispebjerg Hospital, Department of Medicine B, University of Copenhagen, Denmark.
Munck
B G
BG
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002712:Chlorides / Q000502:physiology*; D005260:Female; D005947:Glucose / Q000378:metabolism; D007082:Ileum / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D007930:Leucine / Q000378:metabolism; D011392:Proline / Q000378:metabolism; D011817:Rabbits; D012964:Sodium / Q000502:physiology; D015091:beta-Alanine / Q000031:analogs & derivatives / Q000378:metabolism
D000596:Amino Acids; D002712:Chlorides; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; D011392:Proline; D012964:Sodium; D007930:Leucine; D005947:Glucose