Potassium: From Physiology to Clinical Implications

Abstract

Background: Potassium (K⁺) is the major intracellular cation, with 98% of the total pool being located in the cells at a concentration of 140-150 mmol/l, and only 2% in the extracellular fluid, where it ranges between 3.5 and 5 mmol/l. A fine regulation of the intracellular-extracellular gradient is crucial for life, as it is the main determinant of membrane voltage; in fact, acute changes of K⁺ plasma levels may have fatal consequences. Summary: An integrated system including an ‘internal' and ‘external' control prevents significant fluctuations of plasma levels in conditions of K⁺ loading and depletion. The internal control regulates the intra-extracellular shift, a temporary mechanism able to maintain a constant K⁺ plasma concentration without changing the total amount of body K⁺. The external control is responsible for the excretion of the ingested K⁺, and it has the kidney as the major player. The kidney excretes nearly 90% of the daily intake. Along the proximal tubule and the thick ascending limb on Henle's loop, the amount of K⁺ reabsorption is quite fixed (about 80-90%); conversely, the distal nephron has the ability to adjust K⁺ excretion in accordance with homeostatic needs. The present review analyzes: (1) the main molecular mechanisms mediating K⁺ reabsorption and secretion along the nephron; (2) the pathophysiology of the principal K⁺ derangements due to renal dysfunction, and (3) the effect of ingested K⁺ on blood pressure and renal electrolyte handling. Key Messages: Maintaining plasma K⁺ levels in a tight range is crucial for life; thus, multiple factors are implicated in K⁺ homeostasis, including kidney function. Recent studies have suggested that K⁺ plasma levels, in turn, affect renal salt absorption in animal models; this effect may underlie the reduction of blood pressure observed in hypertensive subjects under K⁺ supplementation.

Tuning Intermediate Filament Mechanics by Variation of pH and Ion Charges

“…As measuring buffers we used 2 mM PB at varying pH (5.8 -8.5) and concentrations of KCl (0, 50, 100, 150 mM) or MgCl 2 (0, 5, 10 mM) (Carl Roth, Germany). The physiological KCl concentration up to 150 mM, 40 which corresponds to the upper c(KCl) used here. The highest c(MgCl 2 )=10 mM used in this study is the threshold concentration observed for collapse of vimentin networks.…”

The importance of the thick ascending limb of Henle’s loop in renal physiology and pathophysiology

“…These channels perform a dual crucial role in the TAL: first, they ensure K + recycling to the lumen, essential for salt reabsorption; second, they set a positive transepithelial voltage, that drives paracellular reabsorption of cations. 13,14 Additional Na + reabsorption is driven by the generated electrical field through the paracellular way; moreover, other cations (Ca 2+ and Mg…”

Hypokaliämie

“…Obwohl der Kausalzusammenhang bisher nicht eindeutig bewiesen ist, gibt es eine Reihe von plausiblen Mechanismen, die den Einfluss von Kalium auf die Blutdruckregulation erklären können. Dabei werden v. a. hormonelle Veränderungen, eine sekundäre Natriumretention und eine direkte Wirkung auf die glatte Gefäßmuskulatur diskutiert [6]. Interessant ist in diesem Zusammenhang die Gruppe der Peritonealdialysepatienten, die im Gegensatz zu Hämodialysepatienten in bis zu 35 % der Fälle an einer relevanten Hypokaliämie leiden [7].…”