What is the predominant cation in the intracellular fluid (ICF)?

From the Guidelines

The predominant cation in the intracellular fluid (ICF) is potassium (K+). Potassium is maintained at a high concentration inside cells, typically around 140-150 mEq/L, which is significantly higher than its concentration in the extracellular fluid (3.5-5.0 mEq/L) 1. This concentration gradient is essential for proper cellular function and is maintained by the sodium-potassium ATPase pump in the cell membrane. The pump actively transports potassium into the cell while moving sodium out, creating an electrochemical gradient that is crucial for nerve impulse transmission, muscle contraction, and maintaining cell volume.

Key Points

• The high intracellular potassium concentration also contributes to the resting membrane potential of cells, which is vital for electrical signaling in neurons and muscle cells 1.
• Disruptions in potassium balance can lead to serious physiological consequences, including cardiac arrhythmias, muscle weakness, and neurological dysfunction.
• Approximately 98% of total body K+ is located in the intracellular space and only 2% in the extracellular space 1.
• The severity of hyperkalaemia can be classified as mild (>5.0 to <5.5 mEq/L) to moderate (5.5 to 6.0 mEq/L) and to severe at thresholds (>6.0 mEq/L) 1.

Clinical Implications

• Hyperkalaemia may be responsible for cardiac arrhythmias leading to cardiac arrest and death, with a resulting increase in mortality 1.
• The occurrence of hyperkalaemia differs between in- and outpatients, and its prevalence increases with the severity of renal impairment 1.
• Hyperkalaemia frequently occurs in patients with cardiovascular diseases, in particular when combined with renal function impairment, diabetes, and advanced age 1.

From the Research

Predominant Cation in Intracellular Fluid (ICF)

• The predominant cation in the intracellular fluid (ICF) is potassium (K+) 2, 3, 4, 5, 6.
• Potassium plays a key role in determining the transmembrane potentials of "excitable membranes" present in nerve and muscle cells 2.
• The concentration of potassium in the intracellular fluid is approximately 140 to 150 meq/liter, while in the extracellular fluid it is approximately 3.5 to 5 meq/liter 4.
• The maintenance of the serum potassium concentration is a complex bodily function and results from the balance between intake, excretion, and distribution between intracellular and extracellular space 4.

Importance of Potassium Balance

• Abnormalities of potassium balance can manifest as skeletal and cardiac muscle dysfunction 3.
• Hyperkalemia can result from renal failure, uroperitoneum, or severe dehydration and acidosis, while hypokalemia can occur due to reduced forage intake, increased gastrointestinal losses, or increased renal losses 3.
• Dyskalemia is a frequent electrolyte imbalance observed among maintenance hemodialysis patients, and can be life-threatening 6.

Regulation of Potassium Balance

• The regulation of potassium balance depends on various factors, including prior potassium intake, intracellular potassium, delivery of sodium chloride and poorly reabsorbable anions to the distal nephron, urine flow rate, and hormones such as aldosterone and beta-catecholamines 4.
• Pharmacologic agents such as diuretics, alpha- and beta-catechol antagonists and agonists, depolarizing agents, and digitalis can alter potassium distribution across cell membranes and/or renal excretion 4.