Analysis of two chloride requirements for sodium-dependent amino acid and glucose transport by intestinal brush-border membrane vesicles of fish.
Intestinal brush border vesicles of a Mediterranean sea fish (Dicentrarchus labrax) were prepared using the Ca2+-sedimentation method. The transport of glucose, glycine and 2-aminoisobutyric acid is energized by an Na+ gradient (out greater than in). In addition, amino acid uptake requires Cl- in the extravesicular medium (2-aminoisobutyric acid more than glycine). This Na+- and Cl--dependent uptake is electrogenic, since it can be stimulated by negative charges inside the vesicles. The specific Cl- requirement of glycine and 2-aminoisobutyric acid transport is markedly influenced by pH, a change from 6.5 to 8.4 reducing the role played by Cl-. In the presence of Cl-, the Km of 2-aminoisobutyric acid uptake is reduced and its Vmax is enhanced. Cl- affects also a non-saturable Na+-dependent component of this amino acid uptake. Amino acid transport is also increased by intravesicular Cl- (2-aminoisobutyric acid less than glycine). This effect is more concerned with glucose uptake, which can be then multiplied by 2.3. A concentration gradient (in greater than out) as well as the presence of Na+ in the incubation medium seems to enter into this requirement. This intravesicular Cl- effect is not influenced by pH between 6.5 and 8.4.
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism*; D005399:Fishes; D005947:Glucose / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007422:Intestines / Q000648:ultrastructure*; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D012964:Sodium / Q000378:metabolism*; D014634:Valinomycin / Q000494:pharmacology
D000596:Amino Acids; D002712:Chlorides; D014634:Valinomycin; D012964:Sodium; D005947:Glucose