Potassium

Description

There are estimated to be approximately 250 grams of potassium present in the adult human body. Most of the potassium in the body is intercellular and, reciprocally, most of the body's sodium is extracellular.

The movement of potassium into extracellular fluid from muscle cells is an important part of the contraction mechanism of muscle tissue.

Potassium is pumped into the cell by active transport systems, which concomitantly pump sodium out of the cell. The preferential segregation of sodium and potassium across the cell's biological membrane is important in maintaining osmotic balance, the electrochemical gradient of membranes, and the regulation of extracellular fluid volume. This mechanism of ion pumping is also instrumental in the restoration of potassium/sodium gradient after the ionic transmission of nerve impulses.

Potassium is important in preserving the acid/base balance of the body, and is an elemental constituent of blood platelets.

Method of Action

Potassium is principally found within cellular fluids and its counterpart, sodium, is mostly found within the extracellular fluids. The segregation of these two ions occurs by means of an adenosine triphosphate (ATP) driven "pump." The pump consists of two proteins within the cellular membrane which, upon energy release from ATP, transport three sodium molecules to the outside of the cell membrane, while simultaneously bringing in two potassium molecules.

A similar pumping mechanism is used in the transport of glucose from the,intestine into the bloodstream. High sodium concentrations in the intestinal fluids tend to promote the movement of sodium across the mucosal cells of the intestine. As sodium is moved across the cells, glucose is concomitantly moved into the cells. The concentration of glucose within the cells builds up until it begins to diffuse into the bloodstream. The "pump" mechanism pumps the sodium into the blood in exchange for potassium, thereby eliminating sodium buildup within the cell. A similar mechanism is used to transport amino acids. Potassium is an essential constituents of several blood buffer systems. Potassium complexes ionically with the sulfate group of sulfuric acid, thereby reducing the acidity of the system by forming a potassium sulfate salt. Potassium has a similar action in base buffer systems with the conversion of the strong base potassium hydroxide into the relatively neutral water molecule.

After the transmission of a nerve impulse, during which sodium ions are shifted across the nerve's synaptic membrane, potassium and sodium are exchanged by the previously mentioned "pump" mechanism (so as to restore the original sodium concentration on the external side of the membrane). This "pumping" of sodium outside is essential to prepare for subsequent nerve transmission.

Potassium acts to relax muscle contraction in opposition to calcium, which induces contraction.

Potassium is absorbed readily in the small intestine; excess potassium is excreted through the urine. Aldosterone hormone tends to promote potassium excretion in substitution for sodium absorption. This is done by activation of the renal "pump" proteins, which simultaneously exchange potassium for sodium across the biological membrane.

Potassium absorption is hindered by the anti-inflammatory agents colchicine and salicylazosulfapyridine; laxatives such as phenophthalein, cascara sagrada, and bisacodyl; and various antimicrobial agents (e.g., tetracycline, and neomycin).

Properties & Uses

Potassium has been proven to be essential, along with increased protein intake, in the treatment of kwashiorkor.

Potassium supplementation is effective in treatment of potassium deficiency symptoms, which include overall muscle weakness, abdominal bloating, heart abnormalities, as well as weak respiration.

Potassium is recommended for patients with congestive heart failure who must use diuretics regularly; diuretics tend to deplete potassium levels in the body. Potassium supplements may be used to replenish potassium lost during periods of chronic illness and, in some patients, the potassium lost due to stress.

Potassium is also useful in the treatment of acute diarrhea, diabetic coma, congenital renal alkylosis, aldosteronism, and, in the case of surgical patients, to replace lost body potassium.

Consequence of Deficiency

Potassium deficiency rarely occurs as a result of inadequate dietary intake, but rather as a result of excessive diarrhea or vomiting, malnutrition, surgery, or use of diuretics. On occasion, prolonged disease may promote a decrease in potassium levels in the body.

Symptoms of potassium deficiencies include overall muscle weakness, abdominal bloating, weak respiration, and heart abnormalities (possibly heart attack).

Magnesium deficiency can also induce a concomitant potassium deficiency.

Loss of large amounts of potassium can lead to the condition of metabolic alkylosis (elevated blood pH) and prolonged deficiency can enhance the prevalence of high blood cholesterol levels.

Toxicity Factors

Excesses of ionized potassium can accumulate and become toxic in instances of a renal failure to clear excess potassium, rapid intravenous administration, or excess ingestion of potassium chloride (25 grams daily). Symptoms may include diarrhea, weakening of respiration and heart action, and numbness in extremities.

Renal abnormalities can result in a dangerous accumulation of potassium if urinary excretion is not sufficient. This can result in hyperkalemia (elevated serum potassium levels) and possibly provoke cardiac arrest, although this phenomenon is extremely rare.

Recommended Dietary Allowance

age	RNI (mg)
infants/children
0-3 months	800
4-6 months	850
7-12 months	700
1-3 years	800
4-6 years	1100
7-10 years	2000
males
11-14 years	3100
15+ years	3500
females
11-14 years	3100
15+ years	3500
pregnancy	-
lactation	-

For over thirty years, Recommended Daily Amounts has existed in the United Kingdom. It has been used to measure the adequacy of an individual's diet. However, in 1991 the Committee on Medical Aspects of Food Policy (COMA) gave forth a whole new set of figures upon the request of the Department of Health's Chief Medical Officer. Reference Nutrient Intake (RNI) is one of these sets collectively known as "Dietary Reference Values." RNI is an amount of a nutrient that is enough for almost every individuals, even someone who has high needs for the nutrient. This level of intake is, therefore, considerably higher than what most people would need. If individuals are consuming the RNI of a nutrient they are most unlikely to be deficient in that nutrient.

Food Sources

Almond	Apple
Apricot	Avocado
Bacon	Banana
Beans	Beef
Beef liver	Beet greens
Beet	Blackberry
Brazil nut	Bread
Broccoli	Cabbage
Caviar	Celery
Cheese	Chicken
Chicken liver	Chocolate
Clams	Corn
Date	Fish
Garlic	Goose
Green pea	Hot cocoa
Lamb liver	Macadamia nut
Milk	Molasses
Mushroom	Parsnip
Peanut	Potato
Raisins	Swiss chard
Turkey liver	Veal liver

Herbal sources include: Licorice root and Stinging nettle.

Abstracts

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