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

Abstracts

 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 [¹⁴C]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 [¹⁴C]glucose accumulation. The apparent anion conductance had a selectivity of Br^– = I^– = Cl^– >  F^–>> 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]. [¹⁴C]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 [¹⁴C]glucose uptake was increased by 2.80 ± 0.53 fold in Cl^–media compared to gluconate media, n = 6; for wild-type +/+, 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.