title: Effect of pH on the transport of Krebs cycle intermediates in renal brush border membranes.
abstract: Lowering extravesicular pH stimulated Na+-dependent citrate transport in renal brush border membrane vesicles: e.g., at pHout = 5.5, the initial rate of citrate uptake was increased 10-fold compared to parallel control experiments at pH 7.5. The same experimental conditions had little effect on succinate uptake. The influence of pH on citrate transport is a product of the extravesicular H+ concentration; pH gradients did not potentiate the effects nor were proton gradients capable of driving transport in the absence of Na+. The effect of pH is adequately explained if only the mono- and divalent species of citrate (Cit1-, Cit2-) are considered acceptable substrates for transport. The stimulatory influence of pH on transport correlated quite well with pH-related increases in the concentrations of Cit1- and Cit2-, and over the same pH range [Cit3-] was inversely related to citrate uptake. A model of the Na+-dependent dicarboxylate transport system is discussed in which three sodium ions are translocated per molecule of dicarboxylic acid.
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism*; D002951:Citrates / Q000378:metabolism*; D002952:Citric Acid Cycle; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000494:pharmacology
chemical_list: D002951:Citrates; D012964:Sodium