Figure 9.
Effect of proximal tubule (PT)-specific Na+-bicarbonate cotransporter, electrogenic, isoform 1 (NBCe1) deletion [PT-NBCe1-A/B knockout (KO)] on serum and urine electrolyte responses to acid loading. A: serum K+, which did not differ significantly between wild-type (WT) and KO mice [WT: 4.10 ± 0.08 mmol/L and KO: 4.56 ± 0.24 mmol/L, n = 6 male (M)/6 female (F) and 2M/4F mice, respectively, P = not significant (NS)]. B: serum , which was significantly lower in KO mice than in WT mice (WT: 13.1 ± 0.7 mmol/L and KO: 5.6 ± 0.9 mmol/L, n = 6M/6F and 2 M/4F mice, respectively, P < 0.001). C: urine ammonia excretion measured in 24-h urine samples. Baseline ammonia excretion did not differ between WT and KO mice. WT mice responded to the acid-loading diet with a rapid increase in ammonia excretion. In KO mice, ammonia excretion was significantly less than in WT mice on each day of acid loading. Furthermore, in KO mice, ammonia excretion decreased slightly from baseline on day 1 of acid loading and then did not increase significantly from baseline rates during days 2 or 3 of acid loading. n = 4−6M/5−6F mice for each genotype at each time point. D: urine pH. Urine pH was significantly more acidic in KO mice than in WT mice on each day prior to acid loading and on each day of acid loading. n = 4−6M/5−6F mice for each genotype at each day. Statistical analysis used ANOVA with genotype, diet, and sex as independent variables. Sex did not significantly alter the effects of genotype. Quantitative measures over time, such as urine ammonia and pH, were analyzed using general linear modeling with repeated measures to determine genotype effects. The statistical significance of specific day measures was determined using Student’s t test.