Abstract
The Na+/H+ exchangers (NHEs) comprise a family of membrane proteins that catalyze the electroneutral exchange of Na+ and H+. Calcineurin homologous protein (CHP) acts as a crucial cofactor for NHE activity through direct interaction with the carboxyl-terminal tail region of NHEs. We have cloned a new rat CHP isoform (rCHP2) and characterized the binding property to NHEs and the tissue distribution. rCHP2 binds to the juxtamembrane region of plasma membrane-type NHE isoforms (NHE1-5) in vivo and in vitro as well as rCHP1 (original rat CHP). Interestingly, CHP2 is predominantly expressed in the small and large intestine although rCHP1 shows relatively ubiquitous expression at both the mRNA and protein levels. In situ hybridization experiments demonstrated the abundant expression of CHP2 in the epithelial cell layer of villi of the small intestine in contrast with the expression of CHP1 in both the epithelial layer and connective tissues. These results suggest that CHP2 functions in the absorptive epithelium for the intestine with NHE(s).
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