Nhe1 is a luminal Na⁺/H⁺ exchanger in mouse choroid plexus and is targeted to the basolateral membrane in Ncbe/Nbcn2-null mice

Abstract

The choroid plexus epithelium (CPE) secretes the major fraction of the cerebrospinal fluid (CSF). The Na(+)-HCO(3)(-) transporter Ncbe/Nbcn2 in the basolateral membrane of CPE cells is important for Na(+)-dependent pH(i) increases and probably for CSF secretion. In the current study, the anion transport inhibitor DIDS had no effect on the residual pH(i) recovery in acidified CPE from Ncbe/Nbcn2 knockout mouse by 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)-fluorescence microscopy in the presence of CO(2)/HCO(3)(-) (Ncbe/Nbcn2-ko+DIDS 109% of control, P = 0.76, n = 5). Thus Ncbe/Nbcn2 mediates the DIDS-sensitive Na(+)-dependent pH(i) recovery in the CPE. The Na(+)/H(+) exchanger-1 Nhe1 is proposed to mediate similar functions as Ncbe/Nbcn2 in CPE. Here, we immunolocalize the Nhe1 protein to the luminal membrane domain in mouse and human CPE. The Na(+)-dependent pH(i) recovery of Nhe1 wild-type (Nhe1-wt) mice in the absence of CO(2)/HCO(3)(-) was abolished in the Nhe1 knockout CPE (Nhe1-ko 0.37% of Nhe1-wt, P = 0.0007, n = 5). In Ncbe/Nbcn2-ko mice, Nhe1 was targeted to the basolateral membrane. Nevertheless, the luminal Na(+)-dependent pH(i) recovery was increased in Ncbe/Nbcn2-ko compared with wild-type littermates (Nhe1-ko 146% of Nhe1-wt, P = 0.007, n = 5). Whereas the luminal Nhe activity was inhibited by the Nhe blocker EIPA (10 microM) in the Ncbe/Nbcn2-wt, it was insensitive to the inhibitor in Ncbe/Nbcn2-ko (Ncbe/Nbcn2-ko+EIPA 100% of control, P = 0.98, n = 5). This indicates that a luminal EIPA-insensitive Nhe was induced in Ncbe/Nbcn2-ko CPE and that EIPA-sensitive Nhe activity was basolateral. The Nhe1 translocation in Ncbe/Nbcn2-ko CPE may reflect a compensatory response, which provides the cells with better means of regulating pH(i) or transporting Na(+) after Ncbe/Nbcn2 disruption.

Severe Neurologic Impairment in Mice with Targeted Disruption of the Electrogenic Sodium Bicarbonate Cotransporter NBCe2 (Slc4a5 Gene)

“…Future studies are required to determine the exact molecular signaling mechanism(s) involved. Interestingly, a recent study showed that loss of the choroid plexus NCBE transporter resulted in basolateral rather than apical expression of NHE1 (28). This finding as well as the significant changes in the modeling of CPE cells due to loss of NBCe2 complements recent studies that have demonstrated that certain ion transporting proteins have additional important and unexpected roles in generating and maintaining the structural properties of epithelial cells and neurons.…”

Na+-dependent HCO3− Import by the slc4a10 Gene Product Involves Cl− Export

“…The ␤ tot was calculated as the sum of the intrinsic buffering power (␤ int ) and the contribution of the CO 2 /HCO 3 Ϫ buffering system as previously described (10,11) (Fig. 1C) (Fig.…”

The Divergence, Actions, Roles, and Relatives of Sodium-Coupled Bicarbonate Transporters

“…That is to say, certain NBCn1-directed polyclonal antibodies suggest a different transporter distribution than others. Some studies report that the localization of NBCn1 in a tissue may vary among species (485) and even among mouse strains (216). Data concerning NBCn1 protein distribution come from the use of the three types of antibodies, those that are generated against: 1) epitopes in the Ct of rat NBCn1 (1014), 2) epitopes in the Ct of human NBCn1 ("anti-NBC3"; Ref.…”

“…In light of the prominent role played by NBCn2 in CSF secretion (429), it has been suggested that the role played by NBCn1 in CSF formation may be less significant. Indeed, in some strains of mice, NBCn1 in the CPE is predominantly at the apical membrane (216,470), where the protein would not be in a position to contribute to CSF secretion. Moreover, in NBCn2 and NBCe2 knockout mice, endogenous NBCn1 does not compensate for defective CSF secretion (216,470).…”