Potassium in biology

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Potassium is the main intracellular ion for all types of cells. In metazoa K+ intracellular concentration is much higher than its extracellular concentration. In this sense K+ is somewhat opposite to Na+, for which situation is of the opposite. The normal level of extracellular potassium ranges from 3.5 to 5.5 mEq/L, although the optimum adult level is 4.5 mEq/L.

[edit] Potassium in nutrition and medicine

Potassium is an essential mineral macronutrient in human nutrition; it is the major cation (positive ion) inside animal cells, and it is thus important in maintaining fluid and electrolyte balance in the body.

Potassium is also important in allowing muscle contraction and the sending of all nerve impulses in animals. See action potential for an explanation of the interplay of sodium and potassium in all excitable animal cells. Because of the interaction of the charge on a potassium ion and its surrounding water molecules, K⁺ ions are actually a little smaller than Na⁺ ions, and ion channels and pumps in cell membranes can easily distinguish between the two types of ions, actively pumping or passively allowing one of the two ions to pass, while blocking the other.

A shortage of potassium in body fluids may cause a potentially fatal condition known as hypokalemia (see article for detail), typically resulting from diarrhea, increased diuresis and vomiting. Deficiency symptoms include muscle weakness, paralytic ileus, ECG abnormalities, decreased reflex response and (in severe cases) respiratory paralysis, alkalosis and arrhythmia.

Eating a variety of foods that contain potassium is the best way to get an adequate amount. Healthy individuals who eat a balanced diet rarely need supplements. Foods with high sources of potassium include orange juice, potatoes, bananas, avocados, apricots, parsnips and turnips, although many other fruits, vegetables, and meats contain potassium. Research has indicated that diets high in potassium can reduce the risk of hypertension.

The 2004 guidelines of the Institute of Medicine specify an RDA of 4,000mg of potassium. However, it is thought that most Americans consume only half that amount per day ([1]). Similarly, in the European Union, particularly in Germany and Italy, insufficient potassium intake is widespread ([2]).

Supplements of potassium in medicine are most widely used in conjunction with the most powerful classes of diuretics, which rid the body of sodium and water, but have the side effect of also causing potassium loss in urine. A variety of medical supplements are available.

Some people with kidney disease are advised to avoid large quantities of dietary potassium. End stage renal failure patients undergoing therapy by renal dialysis must observe strict dietary limits on potassium intake, since the kidneys control potassium excretion, and buildup of blood concentrations of potassium may trigger fatal heart dysrhythmias.