NCC regulation by WNK/SPAK pathway is influenced by alkalosis

Abstract

The WNK/SPAK “potassium-switch” pathway provides a homeostatic mechanism that activates the sodium chloride cotransporter, NCC, to limit urinary potassium excretion in dietary potassium deficiency at the expense of increasing salt-sensitivity and blood pressure. Although it is well understood that high dietary potassium turns off the switch, and decreases NCC activity, several reports suggest the counter anion in potassium-rich diets may have an influence on the pathway. The goal of the present study was to determine if the chronic response to a high K diet depends on the counter anion. Wild-type C57BL6J mice were randomized to control (1%K+), potassium chloride (KCl: 5%K+), or potassium bicarbonate (KHCO3: 5%K+) diets, and physiological, molecular, and imaging analyses were performed at 4 and 10 days of diet consumption. In contrast to the classic response to high KCl diet, characterized by reduced NCC phosphorylation and membrane localization, NCC phosphorylation and apical localization increased after 10 days on the high KHCO3 diet. This response was paralleled by increased phosphorylation of the downstream potassium-switch kinase, SPAK, which in turn phosphorylates NCC. Immunofluorescence imaging revealed WNK4 bodies were more numerous and larger in the high KHCO3 group compared to the control, consistent with activation of upstream WNK signaling. Urine excretion studies revealed mice on the high KHCO3 retain more Na+ than mice on control or KCl diets, paralleling enhanced NCC activation. Unlike mice on the high KCl diet, mice on the high KHCO3 diet develop and maintain metabolic alkalosis and do not exhibit profound hyperkalemia, coincident with more robust activation of ENaC and ROMK than with the high KCl diet. In summary, these data identify an unexpected NCC activation mechanism that may limit distal sodium delivery to prevent excessive potassium losses when alkalosis super activates potassium secretion in more distal segments. NIDDK, LeDucq Foundation This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.