Phosphate transport by rat intestinal basolateral-membrane vesicles.
The characteristics of phosphate transport across intestinal basolateral membranes of the rat were determined by using enriched preparations in which uphill Na+-dependent D-glucose transport could not be demonstrated, but ATP-dependent Ca2+ transport was present. Phosphate transport was saturable, Na+-dependent and exhibited Michaelis-Menten kinetics. Vmax. was 51.1 +/- 4.2 pmol/10 s per mg of protein and Km was 14 +/- 3.9 microM. The transport process was electroneutral. Tracer-exchange experiments and counter-transport studies confirmed the presence of a Na+-Pi carrier at the basolateral membrane. The presence of inside-positive membrane potential did not enhance phosphate uptake, indicating that the Na+ effect is secondary to the presence of the Na+-Pi carrier rather than an induction of positive membrane potential. The stoichiometry of this carrier at pH 7.4 was 2 Na+:1 phosphate, as shown by direct studies utilizing the static-head method. These studies are the first to determine the presence of a phosphate carrier at the basolateral membrane.
Ghishan
F K
FK
Vanderbilt University Medical Center, Department of Pediatrics, Nashville, TN 37232.
Kikuchi
K
K
Arab
N
N
D000818:Animals; D001485:Basement Membrane / Q000378:metabolism; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D066298:In Vitro Techniques; D007583:Jejunum / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D009994:Osmolar Concentration; D010710:Phosphates / Q000378:metabolism*; D051381:Rats; D012964:Sodium / Q000378:metabolism
D010710:Phosphates; D012964:Sodium; D005947:Glucose; D002118:Calcium