- Not to be confused with intercellular, meaning "between cells".
It is used in contrast to extracellular (outside the cell). The cell membrane (and, in many organisms, the cell wall) is the barrier between the two, and chemical composition of intra- and extracellular milieu (Milieu intérieur) can be radically different. In most organisms, for example, a Na+/K+ ATPase maintains a high potassium level inside cells while keeping sodium low, leading to chemical excitability. This terms also means existing within the cells.
- "Definition of Intracellular".
- Matsudaira, Paul T.; Lodish, Harvey F.; Arnold Berk; Kaiser, Chris; Monty Krieger; Matthew P Scott; Anthony Bretscher; Hidde Ploegh (2008). Molecular cell biology. San Francisco: W.H. Freeman. ISBN 0-7167-7601-4.
- Benito B, Garciadeblás B, Schreier P, Rodríguez-Navarro A (April 2004). "Novel p-type ATPases mediate high-affinity potassium or sodium uptake in fungi". Eukaryotic Cell 3 (2): 359–68. PMC 387655. PMID 15075266.