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2016 ; 2
(2
): 72-9
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Potassium: From Physiology to Clinical Implications
#MMPMID27536695
Zacchia M
; Abategiovanni ML
; Stratigis S
; Capasso G
Kidney Dis (Basel)
2016[Jun]; 2
(2
): 72-9
PMID27536695
show ga
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.
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