| slow channel-blocking agent | calcium channel-blocking agent |
|---|---|
| sodium channel | <neurology, physiology> The protein responsible for electrical excitability of neurons. A transmembrane ion channel, containing an aqueous pore around 0.4nm diameter, with a negatively charged region internally (the selectivity filter) to block passage of anions. The channel is voltage gated: it opens in response to a small depolarisation of the cell (usually caused by an approaching action potential), by a multistep process. Around 1000 sodium ions pass in the next millisecond, before the channel spontaneously closes (an event with single step kinetics). The channel is then refractory to further depolarisations until returned to near the resting potential. There are around 100 channels per square micron in unmyelinated axons, in myelinated axons, they are concentrated at the nodes of Ranvier. The sodium channel is the target of many of the deadliest neurotoxins. (18 Nov 1997) |
| delayed rectifier channel | <physiology> The potassium selective ion channels of axons, so called because they change the potassium conductance with a delay after a voltage step. The name is used to denote any axon like K channel. Various roles for example regulation of pacemaker potentials, generation of bursts of action potentials or generation of long plateaus on action potentials. (18 Nov 1997) |
| double-channel catheter | A catheter with two lumens, allowing irrigation and aspiration. Synonym: two-way catheter. (05 Mar 2000) |
| ion channel | <cell biology> A transmembrane pore that presents a hydrophilic channel for ions to cross a lipid bilayer down their electrochemical gradients. Some degree of ion specificity is usually observed and typically a million ions per second may flow. Channels may be permanently open, like the potassium leak channel or they may be voltage gated, like the sodium channel or ligand gated like the acetylcholine receptor. (27 Oct 1998) |
| ion channel gating | The opening and closing of ion channels due to a stimulus. The stimulus can be a change in membrane potential (voltage-gated), drugs or chemical transmitters (ligand-gated), or a mechanical deformation. Gating is thought to involve conformational changes of the ion channel which alters selective permeability. (12 Dec 1998) |
| transnexus channel | A hexagonal 15-20A |
| ligand-gated channel | A class of ion channel's whose ionic permeability is regulated by cell membrane receptors that respond to specific extracellular chemical signals. (05 Mar 2000) |
| ligand gated ion channel | A transmembrane ion channel whose permeability is increased by the binding of a specific ligand, typically a neurotransmitter at a chemical synapse. The permeability change is often drastic, such channels let through effectively no ions when shut, but allow passage at up to 10exp7 ions sexp 1 when a ligand is bound. Recently, the receptors for both acetylcholine and GABA have been found to share considerable sequence homology, implying that there may be a family of structurally related ligand gated ion channels. (18 Nov 1997) |
| benzoylpas calcium | 4-Benzamidosalicylic acid calcium salt;an antituberculous agent. (05 Mar 2000) |
| calcium | <element> An element taken in through the diet that is essential for a variety of bodily functions, such as neurotransmission, muscle contraction and proper heart function. Imbalances of calcium can lead to many health problems and excess calcium in nerve cells can cause their death. (22 May 1997) |
| calcium-45 | <radiobiology> Most easily available of the radioactive calcium-45 isotopes; beta-emitter with a half-life of 162.7 days; used as a tracer. (05 Mar 2000) |
| calcium-47 | <radiobiology> A radioisotope of calcium with a half-life of 4.54 days, used in the diagnosis of disorders of calcium metabolism. (05 Mar 2000) |
| calcium alginate | A topical haemostatic. (05 Mar 2000) |
| calcium aminosalicylate | The calcium salt of p-aminosalicylic acid, with the same uses. (05 Mar 2000) |