Effects of dietary K on cell-surface expression of renal ion channels and transporters.

Changes in apical surface expression of ion channels and transporters in the superficial rat renal cortex were assessed using biotinylation and immunoblotting during alterations in dietary K intake. A high-K diet increased, and a low-K diet decreased, both the overall and surface abundance of the β- and γ-subunits of the epithelial Na channel (ENaC). In the case of γ-ENaC, the effect was specific for the 65-kDa cleaved form of the protein. The overall amount of α-ENAC was also increased with increasing K intake. The total expression of the secretory K(+) channels (ROMK) increased with a high-K diet and decreased with a low-K diet. The surface expression of ROMK increased with high K intake but was not significantly altered by a low-K diet. In contrast, the amounts of total and surface protein representing the thiazide-sensitive NaCl cotransporter (NCC) decreased with increasing K intake. We conclude that modulation of K(+) secretion in response to changes in dietary K intake involves changes in apical K(+) permeability through regulation of K(+) channels and in driving force subsequent to alterations in both Na delivery to the distal nephron and Na(+) uptake across the apical membrane of the K(+) secretory cells.