ALDOSTERONE INDUCTION AND EPITHELIAL DISTRIBUTION OF CHIF

To further characterize the possible role of this gene in epithelial i on transport, we have studied its epithelial distribution and hormonal induction. Northern hybridization indicate that the zonal distributio n of CHIF and mRNA in kidney is: papilla >> medulla >> cortex. High le vels of CHIF were also detected in a primary culture from inner medull ary collecting duct (IMCD). Perfusing rats with <20 nM aldosterone thr ough 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 i ncubation. This response appears to be mineralocorticoid specific; per fusing or injecting rats with maximal doses of dexamethasone did not e voke a further increase in CHIF mRNA. In contrast, high levels of CHIF are expressed in kidney papilla and IMCD primary culture, irrespectiv e of corticosteroid treatment. Thus, like the apical Na+ channel and t he H+-K+-adenosinetriphosphatase, CHIF is mineralocorticoid induced in the colon but constitutively expressed in kidney.