Nhe1 is a luminal Na+/H+ exchanger in mouse choroid plexus and is targeted to the basolateral membrane in Ncbe/Nbcn2-null mice.
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.
Dept. of Anatomy, Aarhus University, DK-8000 Aarhus C, Denmark. hd@ana.au.dk
Helle Hasager
HH
Damkier
Vikram
V
Prasad
Christian Andreas
CA
Hübner
Jeppe
J
Praetorius
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D000584:Amiloride / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001639:Bicarbonates / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000037:antagonists & inhibitors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D016764:Cell Polarity; D027963:Chloride-Bicarbonate Antiporters / Q000037:antagonists & inhibitors / Q000172:deficiency* / Q000235:genetics; D002831:Choroid Plexus / Q000187:drug effects / Q000378:metabolism*; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D021381:Protein Transport; D012964:Sodium / Q000378:metabolism*; D027982:Sodium-Bicarbonate Symporters / Q000037:antagonists & inhibitors / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D001639:Bicarbonates; D027682:Cation Transport Proteins; D027963:Chloride-Bicarbonate Antiporters; D005452:Fluoresceins; D005456:Fluorescent Dyes; C530862:SLC4A5 protein, mouse; C490998:SLC9A1 protein, human; C526208:Slc4a10 protein, mouse; C498904:Slc4a7 protein, mouse; C490997:Slc9a1 protein, mouse; D027982:Sodium-Bicarbonate Symporters; D000074082:Sodium-Hydrogen Exchanger 1; D017923:Sodium-Hydrogen Exchangers; D000584:Amiloride; C043829:2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein; D012964:Sodium; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; C039614:ethylisopropylamiloride