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| 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) |
| alkaline water | A water that contains appreciable amounts of the bicarbonates of calcium, lithium, potassium, or sodium. (05 Mar 2000) |
| aromatic water | 1. To wet or supply with water; to moisten; to overflow with water; to irrigate; as, to water land; to water flowers. "With tears watering the ground." (Milton) "Men whose lives gilded on like rivers that water the woodlands." (Longfellow) 2. To supply with water for drink; to cause or allow to drink; as, to water cattle and horses. 3. To wet and calender, as cloth, so as to impart to it a lustrous appearance in wavy lines; to diversify with wavelike lines; as, to water silk. Cf. Water. 4. To add water to (anything), thereby extending the quantity or bulk while reducing the strength or quality; to extend; to dilute; to weaken. To water stock, to increase the capital stock of a company by issuing new stock, thus diminishing the value of the individual shares. Cf. Water. Origin: AS. Waeterian, gewaeterian. 1. The fluid which descends from the clouds in rain, and which forms rivers, lakes, seas, etc. "We will drink water." ."Powers of fire, air, water, and earth." . Pure water consists of hydrogen and oxygen, H2O, and is a colourless, odorless, tasteless, transparent liquid, which is very slightly compressible. at its maximum density, 39 deg Fahr. Or 4 deg C, it is the standard for specific gravities, one cubic centimeter weighing one gram. It freezes at 32 deg Fahr. Or 0 deg C. And boils at 212 deg Fahr. Or 100 deg C. (see Ice, Steam). It is the most important natural solvent, and is frequently impregnated with foreign matter which is mostly removed by distillation; hence, rain water is nearly pure. It is an important ingredient in the tissue of animals and plants, the human body containing about two thirds its weight of water. 2. A body of water, standing or flowing; a lake, river, or other collection of water. "Remembering he had passed over a small water a poor scholar when first coming to the university, he kneeled." (Fuller) 3. Any liquid secretion, humor, or the like, resembling water; especially, the urine. 4. <pharmacology> A solution in water of a gaseous or readily volatile substance; as, ammonia water. 5. The limpidity and luster of a precious stone, especially a diamond; as, a diamond of the first water, that is, perfectly pure and transparent. Hence, of the first water, that is, of the first excellence. 6. A wavy, lustrous pattern or decoration such as is imparted to linen, silk, metals, etc. See Water, 3, Damask, and Damaskeen. 7. An addition to the shares representing the capital of a stock company so that the aggregate par value of the shares is increased while their value for investment is diminished, or "diluted." Water is often used adjectively and in the formation of many self-explaining compounds; as, water drainage; water gauge, or water-gauge; waterfowl, water-fowl, or water fowl; water-beaten; water-borne, water-circled, water-girdled, water-rocked, etc. Hard water. See Hard. Inch of water, a unit of measure of quantity of water, being the quantity which will flow through an orifice one inch square, or a circular orifice one inch in diameter, in a vertical surface, under a stated constant head; also called miner's inch, and water inch. The shape of the orifice and the head vary in different localities. In the Western United States, for hydraulic mining, the standard aperture is square and the head from 4 to 9 inches above its center. In Europe, for experimental hydraulics, the orifice is usually round and the head from 1/12 of an inch to 1 inch above its top. Mineral water, waters which are so impregnated with foreign ingredients, such as gaseous, sulphureous, and saline substances, as to give them medicinal properties, or a particular flavor or temperature. Soft water, water not impregnated with lime or mineral salts. To hold water. See Hold, To keep one's head above water, to keep afloat; fig, to avoid failure or sinking in the struggles of life. To make water. To pass urine. <medicine> Hydrothorax. Other phrases, in which water occurs as the first element, will be found in alphabetical order in the Vocabulary. Origin: AS. Waeter; akin to OS. Watar, OFries. Wetir, weter, LG. & D. Water, G. Wasser, OHG. Wazzar, Icel. Vatn, Sw. Vatten, Dan. Vand, Goth. Wat, O. Slav. & Russ. Voda, Gr, Skr. Udan water, ud to wet, and perhaps to L. Unda wave. Cf. Dropsy, Hydra, Otter, Wet, Whisky. Source: Websters Dictionary (01 Mar 1998) |
| baryta water | A saturated aqueous solution of barium hydroxide; used as an alkaline reagent. (05 Mar 2000) |
| bitter water | A natural mineral water containing Epsom salt. (05 Mar 2000) |