| potassium channel | Ion channel selective for potassium ions. There are diverse types with different functions, for example: delayed rectifier channels, M channels, A channels, inward rectifier channels, Ca dependent K channels. (18 Nov 1997) |
|---|---|
| single channel recording | Variant of patch clamp technique. (18 Nov 1997) |
| 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) |
| alveolocapillary block | The presence of material that impairs the diffusion of gases between the air in the alveolar spaces and the blood in alveolar capillaries; block can be caused by oedema, cellular infiltration, fibrosis, or tumour, and results in undersaturation of peripheral arterial blood with oxygen. (05 Mar 2000) |
| anterograde block | Conduction block of an impulse traveling anywhere in its ordinary direction, for example, from the sinoatrial node toward the ventricular myocardium. (05 Mar 2000) |
| arborization block | Intraventricular block supposedly due to widespread blockage in the Purkinje ramifications and manifested in the electrocardiogram by a pattern similar to bundle-branch block but with complexes of low amplitude. (05 Mar 2000) |
| atrioventricular block | <cardiology> A conduction disturbance that results in the inappropriate delay (or complete inability) of a electrical impulse, generated in the atria, to reach the ventricles (via the atrioventricular node). Clinical types are divided into first (nonserious), second and third degree (most serious). Some drugs may precipitate atrioventricular block (for example clonidine, methyldopa, verapamil). A permanent pacemaker may be required for a third degree (complete) heart block. (02 Jan 1998) |