Randomized Trial on the Effect of Oral Potassium Chloride Supplementation on the Thiazide-Sensitive Sodium Chloride Cotransporter in Healthy Adults
Aihua Wu, Martin Wolley, Hannah L. Mayr, Lei Cheng, Diane Cowley, Bo Li, Katrina L. Campbell, Andrew S. Terker, David H. Ellison, Paul A. Welling, Robert A. Fenton, Michael Stowasser
Abstract
IntroductionThe putative “renal-K switch” mechanism links dietary potassium intake with sodium retention and involves activation of the sodium chloride (NaCl) cotransporter (NCC) in the distal convoluted tubule in response to low potassium intake, and suppression in response to high potassium intake. This study examined NCC abundance and phosphorylation (phosphorylated NCC [pNCC]) in urinary extracellular vesicles (uEVs) isolated from healthy adults on a high sodium diet to determine tubular responses to alteration in potassium chloride (KCl) intake.MethodsHealthy adults maintained on a high sodium (∼4.5 g [200 mmol]/d) low potassium (∼2.3 g [60 mmol]/d) diet underwent a 5-day run-in period followed by a crossover study, with 5-day supplementary KCl (active phase, Span-K 3 tablets (potassium 24 mmol) thrice daily) or 5-day placebo administrated in random order and separated by 2-day washout. Ambulatory blood pressure (BP) and biochemistries were assessed, and uEVs were analyzed by western blotting.ResultsAmong the 18 participants who met analysis criteria, supplementary KCl administration (vs. placebo) was associated with markedly higher levels of plasma potassium and 24-hour urine excretion of potassium, chloride, and aldosterone. KCl supplementation was associated with lower uEV levels of NCC (median fold change (KCl/Placebo) = 0.74 [0.30–1.69], P < 0.01) and pNCC (fold change (KCl/Placebo) = 0.81 [0.19–1.75], P < 0.05). Plasma potassium inversely correlated with uEV NCC (R2 = 0.11, P = 0.05).ConclusionsThe lower NCC and pNCC in uEVs in response to oral KCl supplementation provide evidence to support the hypothesis of a functional “renal-K switch” in healthy human subjects.