NHE1 (SLC9A1) is present in most cells and is the most extensively characterized member of this family (Sardet C et al, 1989). NHE2-4 (SLC9A2-4) (Malakooti J et al, 1999; Brant SR et al, 1995) are expressed mainly in the kidney and GI tract. NHE5 (SLC9A5) (Baird NR et al, 1999) is highly expressed in neuronal-enriched areas of the CNS.