High dietary K intake inhibits proximal tubule transport.
Academic Article
Overview
abstract
The impact of chronic dietary Kloading on proximal tubule (PT) function was measured using free-flow micropuncture, along with measurements of overall kidney function, including urine volume (UV), glomerular filtration rate (GFR), and absolute (ENa, EK) and fractional (FENa, FEK) Na+ and K+ excretion in the rat. Feeding animals a diet with 5% KCl (HK) for 7 days reduced GFR by 29%, increased UV by 77%, and increased EK by 202% compared with rats on a 1% KCl (CK) diet. HK did not change ENa but significantly increased FENa (1.40 vs. 0.64%), indicating that fractional Na+ absorption is reduced by HK. PT reabsorption was assessed using free-flow micropuncture in anesthetized animals. At 80% of the accessible length of the PT measurements of inulin concentration indicated volume reabsorption of 73% and 54% in CK and HK, respectively. At the same site, fractional PT Na+ reabsorption was 66% in CK and 37% in HK animals. Fractional PT K+ reabsorption was 66% in CK and 37% in HK. To assess the role of the Na-H exchanger NHE3 in mediating these changes we measured NHE3 protein expression in total kidney microsomes as well as surface membranes using Western blots. We found no significant changes in protein in either cell fraction. Expression of the S552 phosphorylated form of NHE3 was also similar in CK and HK animals. Reduction in PT transport may facilitate K+ excretion and help balance Na+ excretion by shifting Na+ reabsorption from K+ -reabsorbing to K+ -secreting nephron segments.
