Studies of oxalate efflux and oxalate transport via anion exchange in rat renal brush border membrane vesicles
Nishibuchi, S.; Okada, Y.; Yoshida, O.
Nihon Jinzo Gakkai Shi 31(1): 57-65
1989
ISSN/ISBN: 0385-2385 PMID: 2747000 Document Number: 328442
In order to study the characteristics of oxalate transport across the brush border membrane, we studied oxalate uptake and efflux by rat renal cortical brush border membrane vesicles (BBMV). The vesicles were prepared with MgCl2 precipitation method and oxalate uptake was measured by a modification of the rapid millipore filtration technique. In order to analyze efflux of oxalate from BBMV, the vesicles were pre-equilibrated with 100 microM [14-C]-oxalate for 10 min, at 30 degrees C. Temperature dependent and independent oxalate uptake were observed under the conditions of salt and anion free medium. Temperature dependent oxalate accumulation showed "over shoot", indicating carrier mediated oxalate flux. The stimulating effect of an inside alkaline pH gradient on oxalate uptake failed to show at intravesicular pH 8.5. The efflux of oxalate from pre-loaded BBMV showed three steps decreasing curve. Initial rapid efflux was inhibited by extravesicular 5 mM para-aminohippurate (PAH) and low temperature (5 degrees C). Extravesicular 100 microM PAH had no effect on oxalate efflux. These data suggested a carrier mediated oxalate transport system across the barrier from intracellular to luminal site. An outwardly directed chloride (Cl) gradient stimulated oxalate uptake in BBMV, DIDS, anion exchange inhibitor, inhibited this Cl-stimulated oxalate uptake completely. Harmaline, a Na-coupled cotransport inhibitor, had no effect and Probenecid, an organic anion transport inhibitor, caused 45% inhibitory effect on Cl-gradient stimulated oxalate transport system via anion exchange in the rat kidney BBMV.