title: Chloride and membrane potential dependence of sodium ion-proline symport.
abstract: Proline accumulation by renal proximal tubule brush border membrane vesicles is Na+ dependent, but little is known about the role of anions or membrane potential on proline uptake. Recent studies in a variety of transport systems, including rat renal brush border membrane vesicles, indicate that halide anions chloride (Cl-) and bromide (Br-) are essential for glycine, beta-alanine, gamma-aminobutyric acid, and taurine uptake, so the possibility that Na(+)-proline symport is Cl- dependent was explored. Also, the role of membrane potential on transport was assessed by determining the effect of external anions with different membrane permeabilities. The ratio of initial rate Cl- stimulated to thiocyanate (SCN)(-)-stimulated uptake values serves to measure Cl- dependence. The initial rate of proline uptake to equilibrium value was 3.11 +/- 0.5 (SE) in the presence of Cl- versus SCN-. The ratio for D-glucose, whose uptake is governed only by electrogenic status of the membrane, was 0.61 +/- 0.47 (P less than 0.001 versus proline). In another series of experiments, uptake values for various anions as a percent of equilibrium (I/E x 100) were: SCN-, 84.9 +/- 10.9; NO3, 49.9 +/- 11.0; SO4(2-), 27.3 +/- 4.4; F-, 68.5 +/- 18.3; Cl-, 164.1 +/- 44.6; Br-, 150.6 +/- 30.2; I-, 56.7 +/- 13.5. The stoichiometry of uptake by Hill plot analysis of proline uptake in the presence of varying concentrations of Na+ (0 to 100 mM) and Cl- (0 to 100 mM) was 2Na+:1Cl-:1 proline.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Pediatrics, University of Tennessee, Memphis 38103.
authors.forename: R W
authors.initials: RW
authors.lastname: Chesney
authors.forename: I
authors.initials: I
authors.lastname: Zelikovic
authors.forename: A
authors.initials: A
authors.lastname: Budreau
authors.forename: D
authors.initials: D
authors.lastname: Randle
mesh_terms: D026921:Amino Acid Transport Systems, Neutral; D000818:Animals; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D066298:In Vitro Techniques; D007672:Kidney Cortex / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials; D008871:Microvilli / Q000378:metabolism; D011392:Proline / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D012964:Sodium / Q000378:metabolism*; D027981:Symporters
chemical_list: D026921:Amino Acid Transport Systems, Neutral; D002352:Carrier Proteins; D002712:Chlorides; D027981:Symporters; D011392:Proline; D012964:Sodium