| patch clamping | <physiology> A specialised and powerful variant of voltage clamping, in which a patch electrode of relatively large tip diameter (5m) is pressed tightly against the plasma membrane of a cell, forming an electrically tight, gigohm seal. The current flowing through individual ion channels can then be measured. Different variants on this technique allow different surfaces of the plasma membrane to be exposed to the bathing medium: the contact just described is a cell attached patch. If the electrode is pulled away, leaving just a small disc of plasma membrane occluding the tip of the electrode, it is called an inside out patch. If suction is applied to a cell attached patch, bursting the plasma membrane under the electrode, a whole cell patch (similar to an intracellular recording) is formed. If the electrode is withdrawn from the whole cell patch, the membrane fragments adhering to the electrode reform a seal across the tip, forming an outside out patch. (15 Mar 2000) |
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| patch-clamp techniques | An electrophysiologic technique for studying cells, cell membranes, and occasionally isolated organelles. All patch-clamp methods rely on a very high-resistance seal between a micropipette and a membrane; the seal is usually attained by gentle suction. The four most common variants include on-cell patch, inside-out patch, outside-out patch, and whole-cell clamp. Patch-clamp methods are commonly used to voltage clamp, that is control the voltage across the membrane and measure current flow, but current-clamp methods, in which the current is controlled and the voltage is measured, are also used. (15 Mar 2000) |
| patch test | A test of skin sensitiveness: a small piece of paper, tape, or a cup, wet with CO non-irritating diluted test fluid, is applied to skin of the upper back or upper outer arm and after 48 hours the area previously covered is compared with the uncovered surface; an erythematous reaction with vesicles occurs if the substance causes contact allergy. See: photo-patch test. (05 Mar 2000) |
| patch tests | Skin tests in which the sensitiser is applied to a patch of cotton cloth or gauze held in place for approximately 48-72 hours. It is used for the elicitation of a contact hypersensitivity reaction. (12 Dec 1998) |
| peyer's patch | One of the lymphatic nodule aggregates existing in the intestines. (09 Oct 1997) |
| photo-patch test | A test of contact photosensitization: after application of a patch with the suspected sensitiser for 48 hours to two sites, if there is no reaction one area is exposed to a weak erythema dose of sunlight or ultraviolet light; if positive, a more severe reaction with vesiculation develops at the exposed patch area than the nonexposed skin patch site. (05 Mar 2000) |
| moth patch | <dermatology> Melasma cholasma hepaticum a term formerly used to refer to circumscribed facial hyperpigmentation resembling melasma that may occur as a cutaneous manifestation of chronic liver disease. Origin: Gr. Chloazein = to be green (18 Nov 1997) |
| whole cell patch | <physiology> A variant of patch clamp technique, in which the patch electrode seals against the cell, with direct communication between the interior of the electrode and the cytoplasm. (18 Nov 1997) |
| mucous patch | An oval to round, yellow-gray to white, membrane-covered lesion or lesions occurring on the mucous membranes; usually seen in secondary syphilis. (05 Mar 2000) |
| salmon patch | Interstitial or parenchymatous keratitis giving rise to neovascularization of the cornea. Synonym: Hutchinson's patch. (05 Mar 2000) |
| herald patch | The initial rapidly enlarging oval-shaped red papulosquamous lesion, usually on the trunk, heralding the widespread eruption of pityriasis rosea, and preceding the latter by 7-14 days. (05 Mar 2000) |
| shagreen patch | An oval-shaped nevoid plaque, skin-coloured or occasionally pigmented, smooth or crinkled, appearing on the trunk or lower back in early childhood; sometimes seen with other signs of tuberous sclerosis. Synonym: shagreen patch. (05 Mar 2000) |
| inside out patch | A variant of the patch clamp technique, in which a disc of plasma membrane covers the tip of the electrode, with the inner face of the plasma membrane facing outward, to the bath. (18 Nov 1997) |
| opaline patch | A mucous patch of silver-gray appearance. (05 Mar 2000) |
| outside out patch | A variant of patch clamp technique, in which a disc of plasma membrane covers the tip of the electrode, with the outer face of the plasma membrane facing outward, to the bath. (18 Nov 1997) |