Chronic K depletion stimulates rat renal brush-border membrane Na-citrate cotransporter

Abstract

Chronic K depletion (KD) causes hypocitraturia. In the present studies, the effect of KD, induced by a low-K diet for 14 days (serum [K] 4.1 +- 0.1, control vs. 2.2 +/- 0.1 meq/l, KD, P less than 0.01), on renal cortical brush-border membrane (BBM) Na-citrate cotransporter activity was examined. KD significantly decreased fractional citrate excretion (3.90 +/- 0.68 vs. 0.53 +/- 0.10%, P less than 0.01). This was paralleled by a significant increase in the initial linear rate of BBM Na-dependent citrate transport (81 +/- 4 vs. 141 +/- 6 pmol citrate.5 s-1.mg protein-1, P less than 0.01). Kinetic studies varying extravesicular citrate concentration demonstrated that KD increased the maximal activity (Vmax) (152 +/- 17 vs. 296 +/- 14 pmol citrate.5 s-1.mg protein-1, P less than 0.01) with no difference in citrate affinity (118 +/- 23, control vs. 135 +/- 22 microM citrate, KD). Similarly, when extravesicular Na concentration was varied, KD increased the Vmax (132 +/- 9 vs. 206 +/- 6 pmol citrate.5 s-1.mg protein-1, P less than 0.01) with no difference in Na affinity (29 +/- 3, control vs. 28 +/- 1 mM Na, KD). The effect of KD on Na-citrate cotransport was specific in that KD did not alter Na-glucose (84 +/- 12, control vs. 89 +/- 5 pmol glucose.5 s-1.mg protein-1, KD) or Na-proline (87 +/- 3, control vs. 84 +/- 5 pmol proline.5 s-1.mg protein-1, KD) cotransport. In conclusion, KD increases the Vmax of the proximal tubule apical membrane Na-citrate cotransporter.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct Effect of CoCl2 and NiCl2 on Citrate Uptake by the Rat Renal Brush Border Membrane

“…Citrate is freely filtered in the glomerulus, and its reabsorption in the proximal tubule is the major determinant of the rate of renal excretion. Proximal citrate reabsorption is an active transport and mediated by an apical Na-citrate cotransporter, which carries three Na + with one citrate 2-, and is thus electrogenic 17) in nature. In this study, we exposed rat renal brush border membrane vesicles (BBMV) to CoCl 2 and NiCl 2 , respectively, and comparatively investigated the direct effect of these exposure on citrate uptake by BBMV to elucidate the renal toxic mechanisms of Co and Ni.…”

Effect of Platinum Coordination Complex (PtCx) on Citrate Uptake by Rat Renal Brush Border Membrane Vesicles (BBMV): Cisplatin-Intoxicated Rats.

“…Citrate is freely filtered at the glomerulus, and its reabsorption in the proximal tubule is the major determinant of the rate of renal excretion 5) . In our previous studies 6, 7) , we reported that the preincubation of rat renal brush border membrane vesicles (BBMV) with 5 mM cisplatin for 4 and 8 hours and 100 mM carboplatin, a second-generation platinum coordination complex, for 8 hours significantly inhibited the citrate uptake compared with that of the control BBMV.…”

Direct Effect of Vanadium on Citrate Uptake by Rat Renal Brush Border Membrane Vesicles (BBMV).

“…Citrate is freely filtered at the glomerulus, and its absorption by the transporters in the proximal tubule is the major determinant of rate 7) . In the present study, we exposed rat renal brush border membrane vesicles (BBMV) to vanadium pentoxide (V 2 O 5 ) and investigated the direct effect of vanadium exposure on the citrate uptake of the BBMV.…”