The intrinsic Cl- conductance of mouse kidney cortex brush-border membrane vesicles is not related to CFTR

Brush-border membrane vesicles (BBMV) were prepared from whole Balb/c mice kidneys by a Mg2+ precipitation technique. The presence of an intrinsic Cl- conductance co-expressed with Na+/glucose cotransport was inferred by the anion dependence of [C-14]glucose uptake and overshoot with inward Na+-anion gradients. In Na+-equilibrated conditions, an inside-negative membrane potential difference (p.d.) produced by an inward Cl- gradient alone was capable of driving intravesicular [C-14]glucose accumulation. The apparent anion conductance had a selectivity of Br- = I- = Cl- > F- much greater than gluconate, was inhibited by 0.5 mM 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) but was unaffected by 0.5 mM 4,4'-diisothiocyanatostilbene 2,2'-disulphonate (DIDS). BBMV were isolated from mice in which the CFTR gene had been disrupted by a termination mutation (-/-) and compared with normal litter mates (+/+) and heterozygotes (-/+)[18]. [C-14]Glucose uptake in NaCl media was significantly greater than glucose uptake in Na gluconate media for all three genotypes measured at 20 s: for homozygous -/- animals [C-14]glucose uptake was increased by 2.80 +/- 0.53 fold in Cl- media compared to gluconate media, n = 6; for wildtype +/+, by 2.16 +/- 0.53 fold, n = 8; and for heterozygous +/- animals, by 2.17 +/- 0.45 fold, n = 8. The observation of a Cl--dependent component in BBMV isolated from homozygous -/- mutant animals shows that the chloride conductance in these vesicles cannot be due to CFTR expression.