Intracellular calcium ([Ca2+]i)

Intracellular calcium (Ca2+) is a ubiquitous second messenger that plays a central role in regulating a vast array of cellular processes, including muscle contraction, neurotransmitter release, and gene transcription [1, 2]. Under physiological conditions, the concentration of cytosolic calcium is maintained at very low levels (approximately 100 nM) compared to the millimolar concentrations in the extracellular fluid and internal stores like the endoplasmic reticulum [3]. This steep gradient allows for rapid, localized increases in calcium levels upon the opening of specialized ion channels, which triggers specific signaling cascades [4]. Dysregulation of calcium homeostasis—characterized by persistent elevations or abnormal oscillations—is a major driver of pathological states such as cardiac arrhythmias, neurodegeneration, and cell death [5]. Although intracellular calcium itself is a chemical species and not a protein target, the various channels, transporters, and sensors that manage its concentration (such as L-type calcium channels or ryanodine receptors) are among the most important therapeutic targets in modern pharmacology [6, 7]. Sources: [1] Berridge MJ, et al., Nat Rev Mol Cell Biol (2003); [2] Clapham DE, Cell (2007); [3] StatPearls, Physiology, Calcium Signaling (2023); [4] PubMed: Calcium as a second messenger; [5] Brini M, et al., Expert Opin Ther Targets (2014); [6] Rang & Dale's Pharmacology; [7] NIH: Calcium Signaling in Disease.

Other names

Cytosolic calciumIntracellular Ca2+Calcium second messengerCytoplasmic calcium

Drugs typically modulate intracellular calcium levels by inhibiting or activating the protein machinery (channels, pumps, and receptors) that regulates calcium entry from the extracellular space or release from internal stores like the sarcoplasmic reticulum.