channel

A furrow, gutter, or groovelike passageway. SEE ALSO: canal. [L. canalis]

- ion c. a specific macromolecular protein pathway, with an aqueous “pore,” that traverses the lipid bilayer of a cell's plasma membrane and maintains or modulates the electrical potential across this barrier by allowing controlled influx or exit of small inorganic ions such as Na⁺, K⁺, Cl⁻, and Ca²⁺. It plays an important role in propagation of the action potential in neurons, but also may control transduction of extracellular signals and contraction in muscle cells. In general, ion channels are characterized by their selectivity for certain ions, their specific regulation or gating of these ions, and their specific sensitivity to toxins.

- ligand-gated c. a class of ion channels whose ionic permeability is regulated by cell membrane receptors that respond to specific extracellular chemical signals.

- transnexus c. a hexagonal 15–20Å hydrophilic c. capable of transporting small ions between cardiac muscle cells.

- voltage-gated c. a class of ion channels that open and close in response to change in the electrical potential across the plasma membrane of the cell; voltage-gated Na⁺ c.'s are important for conducting action potential along nerve cell processes.

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chan·nel 'chan-əl n

1) a usu. tubular enclosed passage

2 a) a passage created in a selectively permeable membrane by a conformational change in membrane proteins see ion channel

b) a protein or cluster of proteins that functions as a channel see CALCIUM CHANNEL BLOCKER

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chan·nel (chanґəl) [L. canalis a water pipe] 1. a passageway through which something flows; see also canalis and groove. 2. ion c.