Potassium is a mineral that carries a positive charge in the body. It is vital for the transmission of electrical impulses by cells. All cells in the body carry an electrical voltage, but some are more active and utilize electrical impulses more frequently, including those in muscles and nerves. Excessive potassium is one condition that can interfere with nerve impulse conduction.
Resting Membrane Potential
The inside of cells, like the outside of cells, are mostly composed of water. The water contains charged minerals, called electrolytes, such as sodium and potassium. The covering of cells is called the cell membrane. It separates the inside and outside of the cells. The membrane contains protein channels that allow sodium and potassium to flow through them when open, and restrict flow when closed. The outside of cells is relatively high in sodium and the inside is relatively high in potassium. This unequal distribution of electrolytes results in the inside of the cell having a negative charge relative to the outside; in other words, it has a negative voltage.
Action Potential
A nerve's electrical impulse, or action potential, begins when sodium channels in a portion of the cell open. Sodium rushes into the cell making it positive. This causes nearby sodium channels to open, and a wave a sodium rushes into the cell down the length of the nerve. The sodium channels close, and the potassium channels open. Potassium rushes out of the cell, making it negative again.
Hyperkalemia
High blood potassium, or hyperkalemia, causes the environment outside the nerve cell to be full of potassium. As a result, after sodium rushes into the cell followed by potassium channels opening, potassium will not readily flow out of the cell. Since potassium flowing out of the cell normally causes it to become negative again, decreased flow of potassium will cause the cells to be more positive.
Causes, Diagnosis and Treatment
High blood potassium is caused by one of three things. The first is excessive intake by an intravenous route; an oral overdose is possible as well, but less likely. The second is the release of potassium from inside the cells, as from a crush injury to muscle tissue, which breaks open cells, spilling the potassium into the blood. The third is damage to the kidneys, which normally remove potassium from blood to the urine. The diagnosis is made from a medical history, physical exam and lab tests that demonstrate high potassium. Temporary treatment lowers potassium through medicines that bind it in the intestines or that cause cells to absorb potassium. Problems in heart electrical activity from high potassium may be stabilized by calcium. It is important to consult a physician for the diagnosis and treatment of high potassium and other conditions.
References
- "Physiology"; Linda S.Costanzo; 4th Ed 2010
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci, et al.; 17th Ed 2008
