Potassium in biology

Potassium is the main intracellular ion for all types of cells. In metazoa K+ intracellular concentration is much higher than its extracellular concentraion. 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.