DIRECT EFFECT OF CADMIUM ON CITRATE UPTAKE BY ISOLATED RAT RENAL BRUSH-BORDER MEMBRANE-VESICLES

High incidence of multiple kidney stone formation has been observed am ong workers exposed to cadmium (Cd). Citrate is known to be a protecti ve factor against renal stone formation. To study the direct effect of cadmium on citrate uptake by the renal brush border membrane, we expo sed isolated rat renal brush border membrane vesicles (BBMV) to cadmiu m and determined their citrate uptake characteristics. BBMV were prepa red by the divalent cation precipitation method. Citrate uptake was me asured by the Millipore rapid membrane filtration technique. Preincuba tion of BBMV with 2 and 10 mM CdCl2 for 1 min significantly inhibited citrate uptake compared with that of BBMV without Cd. Analysis of the time course of citrate uptake during 30-min preincubation of BBMV with 0.5 mM Cd also revealed significant reduction of the uptake compared with that of the control BBMV without preincubation. These findings in dicate that preincubation of BBMV with cadmium results in time-depende nt and concentration-dependent inhibition of citrate uptake.