- Regulation of extracellular fluid potassium concentration is more complicated than that of other electrolytes as an enormous pool of potassium exists intracellularly within cells and can be utilized to rapidly buffer changes to extracellular potassium. In fact, potassium within the intracellular fluid accounts for nearly 98% of the total body K+ whereas only 2% exists within the extracellular fluid. The rapid buffering capacity of the intracellular potassium pool is critical as even small changes in the extracellular fluid potassium concentration can be extremely dangerous. Empirically, the normal range for ECF potassium is between 3.5 mEq/L to 5 mEq/L whereas increased concentrations beyond this can lead to cardiac arrhythmias.
- Given the unique capacity of intracellular potassium to buffer its extracellular concentration, total ECF potassium concentration can be thought of as being regulated by two distinct processes with different time-scales of action. Rapid second-to-minute regulation is largely dependent on the exchange of ECF and ICF potassium, discussed under Internal Potassium Balance. In contrast, long-term regulation of total body potassium stores is achieved by modulating its urinary excretion, discussed under External Potassium Balance.