channel
[chan´el] a passage, cut, or groove through which something can pass or flow across a solid structure.
calcium channel (
calcium-sodium channel) a slow
voltage-gated channel very permeable to calcium ions and slightly permeable to sodium ions, existing in three subtypes designated
L, M, and
N and located throughout the body; calcium channels are the main cause of
action potentials in certain smooth muscles, and the N channels regulate
neurotransmitter release.
fast channel a
protein channel, such as a
sodium channel, that becomes activated relatively quickly; a fast voltage-gated channel has a much lower activation potential than does the slow type. See also
slow channel.
ligand-gated channel a
protein channel that opens in response to the binding of a molecule (the ligand) to the protein, which causes a conformational change in the protein molecule. See also
voltage-gated channel.
potassium channel a slow
voltage-gated channel selective for the passage of potassium ions, found on the surface of a wide variety of cells, including nerve, muscle, and secretory cells; its functions include regulation of cell membrane excitability, regulation of repetitive low frequency firing in some neurons, and recovery of the nerve fiber membrane at the end of the
action potential.
protein channel a watery pathway through the interstices of a protein molecule by which ions and small molecules can cross a membrane into or out of a cell by diffusion; protein channels play a vital role in
depolarization and
repolarization of nerve and muscle fibers, and may have physical characteristics such as shape or diameter that particularly attract certain ions.
water channel a channel in a cell membrane that permits passage of water molecules; chemical substances such as
vasopressin cause the opening of new channels and increase permeability.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.