Hypertension in NBCe2 Deficient Mice Caused by Enhanced ENaC Activity

Abstract

Mutations of the electrogenic Na‐HCO3 cotransporter NBCe2 are associated with hypertension but the detailed pathogenesis is not well understood. Here we showed that up‐regulation of the epithelial Na channel (ENaC) in the distal nephron plays a critical role in hypertension caused by NBCe2 deficiency in mice. Wild type (WT) and NBCe2 knock out (KO) mice were fed an acid diet (1.5% NH4Cl) for 7‐10 days. Mean arterial pressure (MAP) was measured by tail cuff before and after the treatment with amiloride (Amil, 25 mg/L in drinking water). The MAP (mmHg) was higher in KO compared with WT before treatment (KO: 124.5 ± 2.2 vs WT: 110.6 ± 4.4). After treatment, the MAP in both groups dropped to a similar level (KO: 98.4 ± 3.7 vs WT: 99.1 ± 4.4). Western blot showed that the ENaC‐α expression in the kidney cortex was higher in KO compared with WT. Metabolic cage experiments showed that urinary Na excretion increased 3‐fold after Amil treatment (5 mg/kg, ip) in KO, while increasing only 20% in WT. The urinary K excretion also decreased significantly after Amil treatment in the KO but was similar before and after treatment in WT. Micropunture experiments showed that the [K] was significantly higher in the connecting tubule (CNT) of the KO compared with WT (KO: 21.9 ± 0.6 vs WT: 17.9 ± 1.5 mM), while the transepithelial potential (Vte, mV) was significantly lower (KO: ‐3.2 ± 0.2 vs WT: ‐1.6 ± 0.2). After Amil treatment, the Vte increased to ‐0.1 ± 0.2 in KO and 0.7 ± 0.4 in WT. These results show that both the ENaC expression and activity are increased in the KO, which contribute to the hypertension caused by NBCe2 deficiency.