Hormonal and pharmacological modification of plasma potassium homeostasis.

Human skeletal muscles contain the largest single pool of K+ in the body (2600 mmol, 46 times the total K+ content of the extracellular space). Intense exercise may double arterial plasma K+ in one min. This is because of excitation-induced release of K+ from the working muscle cells via K+ channels. This hyperkalemia is rapidly corrected by reaccumulation of K+ into the muscle cells via Na+,K+ pumps, often leading to hypokalemia. Hyperkalemia may also arise from muscle cell damage, excessive oral or intravenous administration of K+, acidosis, renal failure, depolarization of muscle cells with succinyl choline, activation of K+ channels by fluoride poisoning, hyperkalemic periodic paralysis, malignant hyperthermia, inhibition of the Na+,K+ pumps by digitalis glycosides or treatment with nonselective beta blockers. Hyperkalemia may cause arrhythmia and can be treated with beta2 agonists, insulin or hemodialysis. Hypokalemia may be induced by the stimulation of the Na+,K+ pumps in skeletal muscles seen postexercise, or by catecholamines, beta2 agonists, pheochromocytoma, theophylline, caffeine or insulin, by sepsis, myocardial infarction, trauma, burns and heart failure. Rare causes are hypokalemic periodic paralysis, inhibition of K+ channels by barium, chloroquine or barbiturates. Hypokalemia often reflects dietary K+ deficiency, alkalosis, renal or gastrointestinal loss of K+. Hypokalemia is more likely to cause arrhythmia than hyperkalemia and can be treated by oral or intravenous administration of K+ under frequent control of electrocardiogram and plasma K+. Because of their size and high contents of K+, Na+,K+ pumps and K+ channels, the skeletal muscles play a central role in the acute, from min-to-min ongoing regulation of plasma K+. This is decisive for the maintenance of muscle contractility and heart function.