title: Sodium-dependent transport of phosphate by rat liver plasma membrane vesicles.
abstract: Plasma membrane fractions were prepared from homogenates of rat liver by density gradient centrifugation and then used for the formation of right-side-out vesicles. Uptake of Pi into the vesicles is rapid when an inwardly directed sodium gradient is present and an overshoot of uptake occurs indicative of accumulation against a Pi concentration gradient. Initial Pi uptake rate in the presence of a K+ gradient is approx half that seen with Na+, but uptake in the presence of a choline chloride gradient is very slow. An overshoot does not occur with either K+ or choline gradients. The Km(Pi) for the Na-dependent component of Pi uptake is approx. 1 mM and Vmax at 20 degrees C is 0.8 nmol/min per mg protein. The relationship between initial uptake rate and Na+ concentration is sigmoid, with a Hill coefficient of 2.6. It is concluded that the cotransporter resembles that of kidney and intestine in possessing at least two interacting sites for Na+ and that in intact cells the Na+ gradient maintained by the sodium pump ATPase provides the energy for accumulation of Pi against the unfavourable membrane potential.
authors.affiliation: Department of Biochemistry, King's College, London, UK.
authors.forename: M J
authors.initials: MJ
authors.lastname: Younus
authors.forename: P J
authors.initials: PJ
authors.lastname: Butterworth
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008433:Mathematics; D010710:Phosphates / Q000378:metabolism*; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000494:pharmacology*
chemical_list: D010710:Phosphates; D012964:Sodium; D011188:Potassium