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Under normal physiologic conditions, the kidney is the organ chiefly responsible for the maintenance of potassium balance. Knowledge of the physiologic properties of the distal nephron that affect potassium secretion allows for a better understanding of how potassium excretion can be modulated. This article will review the normal renal handling of potassium and the factors responsible for maintaining potassium balance.
Objectives:
1. Describe the normal distribution of body potassium.
2. Discuss the effect of aldosterone on potassium movement.
3. List the renal processes for handling potassium in each nephron segment.
4. Explain the relationship between renal handling of sodium and potassium secretion.
Editor's Note: This article is a continuation of a renal physiology series in the Nephrology Nursing Journal. The articles, which offer continuing education credits and are updates of manuscripts that previously appeared in the journal, are written by experts in nephrology and contain the most up-to-date information and research available.
Potassium (K+) is the most abundant cation in the human body. The total body K+ stores in an adult are approximately 50-55 milliequivalents (mEq)/Kilogram (Kg) body weight with 98% of the K+ located intracellularly. Skeletal muscle has the highest K+ content per unit dry weight and, therefore, contains the bulk of total body K+, while fat and bone have relatively low K+ content. The high intracellular concentration of K+ (150 mEq/L) [L] versus the low extracellular concentration (4-5 mEq/L) is a delicate balance critical for normal cell functions. Before reviewing how renal cells control body K+ content, it is important to understand how individual cells regulate K+ content. The following discussion addresses the mechanisms responsible for maintaining the K+ balance in the intracellular and extracellular fluid compartment of individual body cells.
Potassium Functions
Each body cell must regulate its internal K+ content and concentration in order to regulate cell growth and division, metabolic reactions, acid-base balance, and cell volume. It is also important that appropriate K+ concentration gradients be maintained across nerve and muscle cells so that appropriate electrical polarization of these cells is maintained for normal neuromuscular and cardiac activity. The movement of as little as 1.5%-2% of the cell K+ into the extracellular fluid (ECF) can result in a potentially fatal increase in the plasma K+ concentration.
Sodium-Potassium ATPase Pump