In cell biology, molecular biology and related fields, the word intracellular means "inside the cell".[1]

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.[2][3]

A commonly used notation is to denote the intracellular concentration of a substrate . For example, is the intracellular concentration of Calcium.

See also


  1. "Definition of Intracellular".
  2. 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.
  3. Benito B, Garciadeblás B, Schreier P, Rodríguez-Navarro A (April 2004). "Novel p-type ATPases mediate high-affinity potassium or sodium uptake in fungi" (PDF). Eukaryotic Cell. 3 (2): 359–68. doi:10.1128/ec.3.2.359-368.2004. PMC 387655. PMID 15075266.
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