Expression of rat, renal NHE2 and NHE3 during postnatal development

The current studies were designed to characterize the expression of sodium-hydrogen exchangers NHE2 and NHE3 during rat, renal ontogeny. NHE2 mRNA and immunoreactive protein were more highly expressed at 2 and 3 weeks of age, with declining levels into adulthood. In situ hybridization of NHE2 mRNA localized the message to the renal inner cortex and outer medullary regions and suggested higher mRNA levels in suckling animals as compared to adults. Immunohistochemical analysis of rat kidney with the NHE2 antiserum showed specific staining of the distal convoluted tubules. In contrast, NHE3 mRNA expression was lowest in 2-week animals and higher in older rats, while NHE3 immunoreactive protein showed constant expression levels during development. Additionally uptake experiments utilizing HOE694 showed no change in NHE2 or NHE3 functional protein expression in 2-week-old rats versus adults. We conclude that the developmental increase in NHE2 mRNA and immunoreactive protein expression cannot be detected by functional assays, which suggests that NHE2 does not play a role in sodium absorption by the renal tubules (as has been previously suggested). Additionally, molecular changes seen in NHE3 mRNA expression do not affect functional protein activity, suggesting increased mRNA translational efficiency or protein stability in suckling rats.