Aldosterone induction and epithelial distribution of CHIF

To further characterize the possible role of this gene in epithelial ion transport, we have studied its epithelial distribution and hormonal induction. Northern hybridization indicate that the zonal distribution of CHIF and mRNA in kidney is: papilla >> medulla >> cortex. High levels of CHIF were also detected in a primary culture from inner medullary collecting duct (IMCD). Perfusing rats with <20 nM aldosterone through osmotic minipumps evoked a 22.4 +/- 1.9-fold increase in colonic CHIF. A significant increase was observed 3 h after administrating the corticosteroid, but maximal response was detected only after a 72-h incubation. This response appears to be mineralocorticoid specific; perfusing or injecting rats with maximal doses of dexamethasone did not evoke a further increase in CHIF mRNA. In contrast, high levels of CHIF are expressed in kidney papilla and IMCD primary culture, irrespective of corticosteroid treatment. Thus, like the apical Na+ channel and the H+-K+-adenosinetriphosphatase, CHIF is mineralocorticoid induced in the colon but constitutively expressed in kidney.