| ion pumps | Integral membrane proteins that transport ions across a membrane against an electrochemical gradient. (12 Dec 1998) |
|---|---|
| ion selective electrode | An electrode half cell, with a semi permeable membrane that is permeable only to a single ion. The electrical potential measured between this and a reference half cell (e.g. A calomel electrode) is thus the Nernst potential for the ion. Given that the solution filling the ion selective electrode is known, the activity (rather than concentration) of the ion in the unknown solution can be measured. Commercial ion selective electrodes frequently use a hydrophobic membrane containing an ionophore, such as valinomycin (for potassium) or monensin (for sodium). A pH electrode is made with a thin membrane of pH sensitive (i.e. Proton permeable) glass. (18 Nov 1997) |
| ion-selective electrodes | Electrodes which can be used to measure the concentration of particular ions in cells, tissues, or solutions. (12 Dec 1998) |
| ion transport | The movement of ions across energy-transducing cell membranes. Transport can be active or passive. Passive ion transport (facilitated diffusion) derives its energy from the concentration gradient of the ion itself and allows the transport of a single solute in one direction (uniport). Active ion transport is usually coupled to an energy-yielding chemical or photochemical reaction such as ATP hydrolysis. This form of primary active transport is called an ion pump. Secondary active transport utilises the voltage and ion gradients produced by the primary transport to drive the cotransport of other ions or molecules. These may be transported in the same (symport) or opposite (antiport) direction. (12 Dec 1998) |
| oxonium ion | <chemistry> A positively charged ion that is water with an additional hydrogen atom (H3O). (09 Oct 1997) |
| tetraethylammonium ion | A monovalent cation widely used in neurophysiology as a specific blocker of potassium channels. It is similar in size to the hydrated potassium ion and gets stuck (reversibly) in the channels. (18 Nov 1997) |
| field ion microscope | <instrument> Type of microscopy in which the specimen is illuminated with ions, often gallium ions, that are focussed electrostatically. The ions remove components of the specimen, lower atomic masses first. These are imaged and provide information on elemental distribution with a resolution of perhaps 30 nm. (18 Nov 1997) |
| 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) |
| light-ion fusion | <radiobiology> Light-Ion-Beam-Driven Inertial Confinement fusion, using beams of light ions driven at implosion targets. Pulsed-power driven accelerators are relatively efficient and cost-effective, but beam-focusing is a technical hurdle for this approach. (09 Oct 1997) |
| CD4-positive T-lymphocytes | A critical subpopulation of regulatory T-lymphocytes involved in the induction of most immunological functions. The HIV virus has selective tropism for the t4 cell which expresses the CD4 phenotypic marker, a receptor for HIV. In fact, the key element in the profound immunosuppression seen in HIV infection is the depletion of this subset of T-lymphocytes, which includes both the helper-inducer (T-lymphocytes, helper-inducer) and suppressor-inducer (T-lymphocytes, suppressor-inducer) T-cells. (12 Dec 1998) |
| CD8-positive T-lymphocytes | A critical subpopulation of regulatory T-lymphocytes involved in MHC class I-restricted interactions. They include both cytotoxic T-lymphocytes (T-lymphocytes, cytotoxic) and suppressor T-lymphocytes (T-lymphocytes, suppressor-effector). (12 Dec 1998) |
| gram-positive | <microbiology> Bacteria that retain the stain or that are resistant to decolourisation by alcohol during Gram's method of staining. This is a primary characteristic of bacteria whose cell wall is composed of a thick layer of peptidologlycan containing teichoic and lipoteichoic acid complexed to the peptidoglycan. See: gram-negative (06 Oct 1997) |
| gram-positive asporogenous rods | <microbiology> A gram-positive, non-spore-forming group of bacteria comprising organisms that have morphological and physiological characteristics in common. (12 Dec 1998) |
| gram-positive asporogenous rods, irregular | <microbiology> A group of irregular rod-shaped bacteria that stain gram-positive and do not produce endospores. (12 Dec 1998) |
| gram-positive asporogenous rods, regular | <microbiology> A group of regular rod-shaped bacteria that stain gram-positive and do not produce endospores. (12 Dec 1998) |