title: The use of a potential-sensitive cyanine dye for studying ion-dependent electrogenic renal transport of organic solutes. Uptake of L-malate and D-malate by luminal-membrane vesicles.
abstract: The mechanisms of uptake of dicarboxylic acids by rabbit renal luminal-membrane vesicles were studied by the use of filtration and spectrophotometric techniques as described in an accompanying paper [Kragh-Hansen, Jørgensen & Sheikh (1982) Biochem. J.208, 359-368]. Addition of l- or d-malate to dye-membrane-vesicle suspensions in the presence of Na(+) gradients (extravesicular>intravesicular) resulted in spectral curves indicative of depolarization events. The renal uptake of dicarboxylic acids was dependent on the type of Na(+)-salt anion present and could be correlated with the ability of the anions to penetrate biological membranes (i.e. Cl(-)>SO(4) (2-)>gluconate). Identical results were obtained by a filtration technique with Sartorius membrane filters. The results indicate that the dicarboxylic acids are taken up by the membrane vesicles in an electrically positive form (i.e. Na(+)/substrate coupling ratio 3:1) by an Na(+)-dependent transport system. This proposal was further supported by spectrophotometric experiments with various ionophores such as valinomycin, gramicidin and nigericin. The absorbance changes associated with simultaneous addition of l- and d-malate and spectrophotometric competition studies revealed that the two isomers are taken up by a common transport system. Spectral changes of the dye induced by addition of increasing concentrations of l- or d-malate indicated that the transport system favours the unphysiological d-form rather than the l-form of malate. Furthermore, it was observed that the affinity of both isomers for the transport system was dependent on the concentration of Na(+) in the medium.
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002232:Carbocyanines; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007668:Kidney / Q000378:metabolism*; D008293:Malates / Q000378:metabolism*; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects; D011804:Quinolines; D011817:Rabbits; D012964:Sodium / Q000378:metabolism; D013053:Spectrophotometry; D013237:Stereoisomerism; D013386:Succinates / Q000378:metabolism; D019802:Succinic Acid
chemical_list: D002232:Carbocyanines; D008293:Malates; D011804:Quinolines; D013386:Succinates; C018919:3,3'-diethyloxadicarbocyanine; C030298:malic acid; D012964:Sodium; D019802:Succinic Acid