Disorders of Potassium: Physiology

Abstract

Potassium (K⁺) is the predominant intracellular cation in the body. The intracellular [K⁺] is 140–150 mEq/L; in blood it is 3.5–5 mEq/L. Serum contains a slightly higher concentration of K⁺ than plasma because K⁺ is released from red blood cells during clot formation. Maintenance of a high cellular concentration of K⁺ is necessary for several cellular functions, including growth, nucleic acid and protein synthesis, and regulation of cell volume, as well as pH and enzyme activation. In addition, a high intracellular concentration of K⁺ is essential to the maintenance of the resting membrane potential for cellular excitability and contraction. The high intracellular K⁺ concentration is maintained by the Na/K-ATPase located in the cell membranes of all animal cells. The activity of this enzyme is influenced by a variety of hormones. The kidney is the primary route for K⁺ excretion. In general, K⁺ excretion in the urine, called kaliuresis, parallels dietary intake. The other route for K⁺ excretion is the colon. Under conditions of decreased renal function, K⁺ excretion by the colon is enhanced.