About 98% of the body's potassium is found inside cells, with the remainder in the extracellular fluid including the blood. This concentration gradient is maintained principally by the Na+/K+ pump. Potassium is essential for many body functions, including muscle and nerve activity. The electrochemical gradient of potassium between the intracellular and extracellular space is essential for nerve function; in particular, potassium is needed to repolarize the cell membrane to a resting state after an action potential has passed. Lower potassium levels in the extracellular space cause hyperpolarization of the resting membrane potential. This hyperpolarization is caused by the effect of the altered potassium gradient on resting membrane potential as defined by the Goldman equation. As a result, a greater-than-normal stimulus is required for depolarization of the membrane to initiate an action potential. In the heart,<unk>  causes arrhythmias because of less-than-complete recovery from sodium-channel inactivation, making the triggering of an action potential less likely. In addition, the reduced extracellular potassium (paradoxically) inhibits the activity of the IKr potassium current and delays ventricular repolarization. This delayed repolarization may promote reentrant arrhythmias.
Hypokalemia
Hyponatremia
Hypernatremia
Alkalosis
Hypercalcaemia
Hyperkalemia
Hypocalcemia
Hypermagnesemia