title: Effects of changes in sodium electrochemical potential gradient on p-aminohippurate transport in newt kidney.
abstract: 1. The relation between p-aminohippurate uptake and the electrochemical potential gradient of Na+ (delta muNa+) across the peritubular membrane was examined in newt (Triturus pyrrhogaster) kidney. The delta muNa+ was modified by changing cellular Na+ concentration and/or lowering the electrical potential difference across the peritubular membrane (peritubular membrane potential) 2. Elevation of external K+ concentration or addition of alanine at 40 mM to the medium decreased the delta muNa+ mainly through the depolarization of the cells. Addition of 1 mM ouabain resulted in a decrease in the peritubular membrane potential and increase in cellular Na+ concentration, thus decrease in the delta muNa+. 3. p-Aminohippurate uptake decreased in proportion to the decrease in the delta muNa+ under all experimental conditions, indicating that the maintenance of the delta muNa+ is required for p-aminohippurate transport. 4. All three different experimental conditions, high medium K+ concentration, 40 mM alanine or 1 mM ouabain, increased the apparent Michaelis constant, Kt, without affecting the maximal uptake rate, V, for p-aminohippurate. These results suggests that the delta muNa+, largely the peritubular membrane potential, may affect the association and/or dissociation of p-aminohippurate and Na+ at both interfaces of the peritubular membrane of the proximal tubular cells.
mesh_terms: D000409:Alanine / Q000494:pharmacology; D000618:Aminohippuric Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D004563:Electrochemistry; D005260:Female; D066298:In Vitro Techniques; D007473:Ion Channels; D007668:Kidney / Q000378:metabolism*; D007684:Kidney Tubules / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008564:Membrane Potentials; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D012455:Salamandridae / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*; D014562:Caudata / Q000378:metabolism*; D010130:p-Aminohippuric Acid / Q000378:metabolism*
chemical_list: D000618:Aminohippuric Acids; D007473:Ion Channels; D010042:Ouabain; D012964:Sodium; D000409:Alanine; D011188:Potassium; D010130:p-Aminohippuric Acid