calciumpermeable

Calcium-permeable is a descriptor used for ion channels and some transporters that allow calcium ions (Ca2+) to cross cellular membranes. The term emphasizes a relative permeability to Ca2+ compared with other cations such as sodium (Na+) or potassium (K+), and is often quantified by permeability ratios in biophysical studies. Calcium permeability is determined by the channel’s pore architecture and electrostatic environment, which favor coordination and passage of Ca2+.

In channels, Ca2+ permeability arises from specific structural features in the selectivity filter, commonly involving negatively charged residues and narrow pore regions. This enables Ca2+ to interact with coordinating ligands as it traverses the channel, sometimes at the expense of Na+ permeability. Some channels are highly Ca2+-selective, while others are only moderately permeable to Ca2+ and permit substantial flux of other ions.

Examples of calcium-permeable channels include NMDA receptor channels, which couple synaptic transmission to Ca2+-dependent signaling; voltage-gated calcium channels (Cav) that conduct Ca2+ to trigger muscle contraction and neurotransmitter release; certain members of the TRP channel family; P2X receptor channels; and store-operated channels such as Orai1. Not all channels are calcium-permeable; many are mixed-cation channels with variable Ca2+ permeability.

Physiological relevance centers on calcium’s role as a universal second messenger. Ca2+ influx through calcium-permeable channels activates signaling cascades, regulates gene expression, and modulates exocytosis and muscle contraction. Cellular calcium homeostasis is maintained by buffering proteins and extrusion mechanisms, and dysregulation can contribute to excitotoxicity and disease.