Inhibition by phenylglyoxal of the sodium-coupled fluxes of glucose and phosphate in renal brush-border membranes

The coupling of phosphate and glucose transport to sodium in brush-border membrane vesicles from rat kidney cortex was studied after chemical modification of arginine residues by phenylglyoxal. Phosphate (10 mM) and sodium (20 mM) uptakes were linear for 6 s and stimulated in the presence of their cosubstrate. The sodium:phosphate stoichiometry measured by a direct method was 1.74. Sodium-independent phosphate and glucose influx were found to be unaffected by phenylglyoxylation. Phosphate- or glucose-independent sodium influx also remained unaltered by the treatment. However, phosphate influx measured with sodium was inhibited by 69% and sodium influx measured with phosphate was inhibited by 40%. When these values were corrected for uncoupled fluxes, the sodium influx coupled to phosphate and the phosphate influx coupled to sodium were inhibited by 93 and 95%, respectively. Glucose influx measured in the presence of sodium was inhibited by 36% and sodium influx in the presence of glucose was reduced by 39%. When the values were corrected for diffusion, these inhibitions were 95 and 100%, respectively. We conclude that the coupling of phosphate and glucose to sodium fluxes by the renal carriers requires the participation of arginine residue(s) in the translocation process. Modification of this arginine by phenylglyoxal leads to a marked inhibition of coupling. These results suggest the implication of arginine residues in the molecular coupling for both glucose and phosphate sodium symporters.