title: Phosphate transport by basolateral plasma membranes of human small intestine.
abstract: The characteristics of phosphate transport across the human intestinal basolateral membrane were determined using an enriched preparation in which uphill Na1+-dependent D-glucose transport could not be demonstrated but adenosine triphosphate-dependent calcium transport was present. The human basolateral membrane vesicles were oriented as follows: 64% inside-out vesicles and 36% rightside-out vesicles or sheets, or both. Phosphate transport showed a 3.4-fold transient "overshoot" phenomena in the presence of an inwardly directed sodium gradient. Computerized Michaelis-Menten kinetics for the net active transport component indicated a Vmax of 65 +/- 5 pmol/mg protein per 8 s and a Km of 93 +/- 15 microM. The transport process was electroneutral. Gramicidin D and transstimulation studies confirmed the presence of a Na+-phosphate carrier at the basolateral membrane. Adenosine triphosphate enhanced phosphate uptake, indicating an adenosine triphosphate-dependent phosphate transport process. These studies are the first to determine the presence of a phosphate carrier in human intestinal basolateral membrane.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D001693:Biological Transport, Active; D002118:Calcium / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006096:Gramicidin / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007413:Intestinal Mucosa / Q000378:metabolism*; D007583:Jejunum / Q000378:metabolism; D008564:Membrane Potentials; D009994:Osmolar Concentration; D010710:Phosphates / Q000378:metabolism*
chemical_list: D010710:Phosphates; D006096:Gramicidin; D000255:Adenosine Triphosphate; D005947:Glucose; D002118:Calcium