Proceedings of The Physiological Society

Europhysiology 2018 (London, UK) (2018) Proc Physiol Soc 41, PCA145

Poster Communications

A single gastric K+ load induces acute diuresis in mice

S. Kornvig1, S. L. Svendsen1, C. Larsen1, I. S. Jensen1, J. Leipziger1, M. V. Sørensen1

1. Dept. of Biomedicine, Aarhus University, Århus C, Denmark.

Introduction: K+ balance relies on regulated renal K+ excretion to match variable dietary K+ intake. Upon a K+ rich meal, rapid and effective urinary K+ excretion is obligatory. The renal adaptation to an acute K+ load involves an increase of the driving force for K+ secretion by shifting the distal tubular Na+ reabsorption from being electroneutral (NCC) to electrogenic (ENaC). In addition, K+ secretion in the CD is stimulated by increased luminal flow. Here we asked, if a high K+ intake acutely increases urinary flow. Methods: Mice were K+ challenged through gavage, diets or a combination of these. After K+ loading urinary volume, [K+]u and [Na+]u ,plasma osmolality, [K+]p and [Na+]p were measured. Results: 1) Mice switched from a 1% to a 2% K+ diet increased their diuresis markedly within 12h. 2) Mice switched from a 1% to a 0.01% K+ diet had a biphasic diuretic response. During the first 12h their diuresis decreased, whereas it increased from 12 to 36h. 3) A single K+ load, by gastric gavage, corresponding to 25-50% of daily K+ intake induced diuresis within 30 min. This occurred despite augmented plasma osmolality. [K+]u remained unchanged and therefore the increased urinary K+ excretion depended on the volume effect 4) K+ gavage did not changes urinary creatinine excretion suggesting a constant GFR. 5) Subsequently, a possible direct and acute effect of a plasma [K+] ([K+]bl) increase was tested in isolated perfused mTALs and CDs. An acute [K+]bl increase (from 3.6 to 6.5 mM) did not affect TAL NaCl absorption (measured 5 and 25 minutes post K+ jump). In contrast, the same manoeuver reduced the CDs sensitivity to stimulated AVP-mediated water absorption (measured 10 minutes post K+ jump). Conclusion: Dietary K+ load induces a rapidly on setting diuresis. This increase in urinary volume appears crucial for a powerful K+ elimination since it appears prior to alteration in [K+]u. Based on preliminary data we suggest that the physiological mechanism of K+-induced diuresis involves AVP desensitization of the CD.

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