DIFFERENTIAL REGULATION OF CHIF MESSENGER-RNA BY POTASSIUM INTAKE ANDALDOSTERONE

The channel-inducing factor (CHIF) is an epithelial-specific transmemb rane protein, which is induced by aldosterone in distal colon (but not in kidney) and can evoke K+ conductance in Xenopus oocytes. The curre nt study examined the possibility that CHIF participates in maintainin g K+ balance by assessing its regulation during variations in K+ intak e. In adrenal-intact rats, high-K+ diet stimulated, whereas K+ deficie ncy downregulated, CHIF mRNA both in kidney and colon. The downregulat ion of CHIF observed in rats fed a low-K+ diet for different periods o f time closely correlated with a decrease in plasma K+ but also with c hanges in aldosterone levels. To differentiate between the two, modula tion of CHIF has been studied in adrenalectomized rats with and withou t corticosteroid supplementation. These experiments have demonstrated that a low-K+ intake suppresses CHIF mRNA, irrespective of aldosterone level. On the other hand, the upregulation evoked by a high-K+ load i s apparent only in adrenal-intact rats. This is despite the fact that infusing rats with aldosterone and corticosterone does not increase th e expression of this mRNA in kidney. These findings may suggest a role for CHIF in preserving K+ balance.