Asymmetry of the Na+-succinate cotransporter in rabbit renal brush-border membranes.
We have investigated the symmetry of Na+-succinate cotransport in rabbit renal brush-border membrane vesicles. Succinate influx and efflux kinetics were measured under voltage-clamped conditions using [14C]succinate and a rapid filtration procedure. Both influx and efflux were Na+-dependent, saturable, temperature-sensitive, and influenced by the trans Na+ and succinate concentrations. The system was judged to be asymmetric, since the maximal velocity for influx was 3-fold higher than that for efflux, and trans Na+ inhibited influx more than efflux. This may be due to the asymmetrical insertion of the transporter in the brush-border membrane, which leads to differences in either the forward and backward translocation rates of the fully loaded carrier or the Na+ and succinate binding constants at the inner and outer faces of the membrane.
D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D007668:Kidney / Q000648:ultrastructure; D007672:Kidney Cortex / Q000378:metabolism*; D007700:Kinetics; D008564:Membrane Potentials; D008871:Microvilli / Q000648:ultrastructure; D011817:Rabbits; D012964:Sodium / Q000378:metabolism*; D013386:Succinates / Q000378:metabolism*; D019802:Succinic Acid; D027981:Symporters
D002352:Carrier Proteins; D013386:Succinates; D027981:Symporters; C042460:sodium-succinate-cotransporter; D012964:Sodium; D019802:Succinic Acid