Sodium-dependent succinate transport in renal outer cortical brush border membrane vesicles

The transport of succinate into outer cortical brush border membrane vesicles (early proximal tubule) was studied. Succinate is taken up into an osmotically active space and exhibits the same distribution volume and the same degree of nonspecific binding and trapping as D-glucose. Succinate uptake is markedly enhanced by sodium and slightly enhanced by lithium but shows no stimulation by other monovalent cations tested. Kinetic analysis of the sodium-dependent component of succinate flux indicates a single transport site obeying Michaelis-Menten kinetics (Km = 1 mM and Vmax = 50 nmol X min -1 X mg protein -1 as measured under zero trans conditions at 100 mM NaCl and 28 degrees C with delta psi = 0). Direct evidence is given that succinate transport is coupled to sodium and is rheogenic, involving the net transfer of positive charge. The sodium:succinate coupling stoichiometry is found to be 2:1 by two independent methods.